Acoustical Treatments Master Thread [Text View] - Page 4

Ethan Winer

01-10-06, 04:37 PM

Tweaks,

> When putting a panel across a corner for bass trapping, is it better or worse to also have a panels along the walls in that corner? <

Probably better, if only because it puts more absorbing material in the room and near the corner.

> The article shows a 705 panel spanning the corner with nothing behind it. <

If you fill the space behind a corner trap it will increase bass absorption even more. But you soon get to a point of diminishing returns, where buying two or three times more rigid fiberglass gives only a small increase in absorption.

Also, just to put into perspective the comparisons of absorption data, understand that all labs are different and they all give different results. Even though these labs are certified and calibrated, they still vary as much as 50 percent (!) at 125 Hz. The variances are not that bad at higher frequencies, but we're talking about bass trapping here so it's important to understand how much these data sheets can vary by.

--Ethan

Tweakophyte

01-11-06, 08:14 AM

myfipie

01-11-06, 08:31 AM

Thanks guys.

I have another one. I looked at some material... burlap will not work for me. Many of the nylon materials are too sheer. Is felt okay? Are there any other good, inexpensive materials that the wife (and I) will like? It looks like speaker cloth is $5-6/yard but at 30" wide, which compares to the ~$3/ yard I was looking at at 72" wide (i.e. 4x the cost).

I will use the same fabric for both the front wall, general abosorbers and the bass traps.

Also, for a 4-6" thick panel spanning the corner at 2', how deep will I have useful bass absorbion? What if that same panel was only 1' wide?

Thanks again,

As far as fabric goes, if you are wanting to hit the hf also then any breathable fabric should be fine..

It is hard to say how much better 6" is with out testing it, but only using 1' wide panels would not work very well. One reason is you need surface area coverage for the room. Second the space behind a 1' panel straddling corners is not enough to efficiently hit the low end.. Stick with 2' panels..

Glenn

tonybradley

01-11-06, 11:30 AM

I apologize for all the questions...just trying to get all the info I can. I've pretty much decided on using OC703 panels for the treatments in my room. I was going to place them vertically at the First Order Reflection Points. The more I read, I'm wondering if it would be better to hang Vertical, or Horizontally? If Horizontally, they would only be 2' high and 4' wide. That would probably hit both points on one wall (possibly). But, would I want to mount them just above my outlets and go 2 feet up, or mount them higher? If doing Horizontally, I was thinking of wrapping about 4 or 5 panels for each wall and attaching them horizontally from front to back. Would this be nonsense? Should I just stick with hanging panels vertically at the reflection points?

rudedoggy

01-13-06, 03:29 PM

I could us some expert advice... I am planning on purchasing soem accoutic foam and some bass traps, but I have a couple of questions first.

1) If I would like to take the accoustic foam - wedge shaped ruffles - and use it at the top of my theatre aong the wall and along the bottom along the floor - like crown molding, will I be shorting my absorbtion? I was thinking about 12" section coming down from the cieling and a 18" to 24" section near the bottom. This "bordering" would be consistent on the 2 side and back walls. I wil also use it in conjunction with corner foam bass traps... Does this sound like a workable solution or will the fact that the middle of the wall is purely drywall ( and some boxed poster) hurt the overall accoustics?

2) I have 4 - 6" columns I made along the side walls. Would it make sense to put 6" bass traps along the sides (the corner area) of each side of each column? Or will the use of 12" traps from ceiling to floor in the back corner of the room be sufficient?

I would appreciate any comments you all might have on the subject and on the subject of placement..

Thanks,
Doggy

bpape

01-14-06, 09:49 AM

Using any treatment just along the top and bottom will still help with decay times somewhat but ignores the reflection points which are most critical and are at ear level approximately.

For the corners, you'll want whatever you can spare. The wider, thicker, and deeper the better. Normally you would do something like straddle a 4" thick material at 45 degrees across the corner floor to ceiling. You can also use the horizontal corners where the wall and ceiling meet if you can't lose the floorspace or have door issues.

Lastly, I'd strongly recommend looking at something other than foam. Don't get me wrong - the Auralex brand is pretty good. The rest are not worth using IMO. For bass absorbtion, I would recommend using OC fiberglass (or equivalent), mineral wool, or acoustical cotton. Dollar for dollar, they'll all do a better job for less money than the foam for bass absorbtion purposes.

Tweakophyte

01-14-06, 10:39 AM

Yesterday I picked up my first batch of JM814 (an OC703 equivalent). I took a few pieces out to play around with. When I was done, I put all five, 2" panels back in the plastic bag and stuck the whole thing in the corner. I had been playing an older Orbital track that has several long, deep, reverse bass sweeps in it. That track has always exposed the FR of the room (i.e. louder and softer portions of the sweep).

Anyway, with the panels shoved into that rear corner there was a night and day difference! The sweep played very flat until I would guess about 40hz. This was just with 4' (tall of stuff in ONE CORNER!

Tweakophyte

01-14-06, 10:40 AM

Now my questions...
I have 2" thick material. I will build frames and wrap them with felt.
- For the front wall I am thinking of building either a 2" or 3" deep frame, and mounting it on the wall. The 3" frame would allow for a 1" air gap. Which configuration is better? If space is a concern, is it worth making the frames even deep (i.e. 4" frame with 2" of material and 2" of air gap)?

- For the side walls I am thinking of either a 3" or 4" deep frame mounted on the wall to cover the first reflection points. This would have 2" of material and an air gap. Comments?

- Inside of my shadow box (see my gallery) I am thinking of doing the same (3" or 4" frame). Space is a small concern here.

- Is 2" of material, wrapped and mounted flush with the ceiling okay, or should I work in an air gap?

- I had a great, initial result from bass trapping in only one corner with 5 pieces of material. How important is symmetry here? My front-right and rear-right corner could hold a 4' tall trap like that fairly easily. My inital plan for a bass trap is a 6" deep frame with foil scrim facing the room. What if I only trapped one corner? What if I did only the right corners? Would it be better to fill one corner (i.e. with the 5 peices) or do two corners with thinner traps. In other words, is it better to have one really thick trap or two thinner traps?

- What is the best way to mount these frames on the wall? I was thinking of putting two nails in the wall and hanging the frame on there. That would pierce through some material that I'll wrap behind a bit. Any other ways? Is it okay to mount these flush to the wall? (If not, I'll probably opt for the thinner version of the frame.)

Thanks!

myfipie

01-14-06, 12:14 PM

I think any of the ways you are thinking of doing this is fine, but here are a few things just to point out.

>Now my questions...
I have 2" thick material. I will build frames and wrap them with felt.
- For the front wall I am thinking of building either a 2" or 3" deep frame, and mounting it on the wall. The 3" frame would allow for a 1" air gap. Which configuration is better? If space is a concern, is it worth making the frames even deep (i.e. 4" frame with 2" of material and 2" of air gap)?<

Leaving gap is a good thing, but you really want to space the panel off the wall to let sound come in from the sides..

>- For the side walls I am thinking of either a 3" or 4" deep frame mounted on the wall to cover the first reflection points. This would have 2" of material and an air gap. Comments?<

Same goes for what I just said...

>- Is 2" of material, wrapped and mounted flush with the ceiling okay, or should I work in an air gap?<

You want to space it off the ceiling by 2"

>- What is the best way to mount these frames on the wall? I was thinking of putting two nails in the wall and hanging the frame on there. That would pierce through some material that I'll wrap behind a bit. Any other ways? Is it okay to mount these flush to the wall? (If not, I'll probably opt for the thinner version of the frame.)<

I think that should be fine.

Glenn

Tweakophyte

01-15-06, 10:20 AM

Glenn-

Thanks for your comments. Regarding the spacing off of the wall to let the sound in, is there any kind of minimum to be effective? I'm really talking about the difference between a crack (say 1/4") and an inch or two.

I am thinking of getting some rubber feet and tapping them into each corner of the frame for spacing away from the wall.

Thanks again,

myfipie

01-15-06, 07:23 PM

>Thanks for your comments. Regarding the spacing off of the wall to let the sound in, is there any kind of minimum to be effective? I'm really talking about the difference between a crack (say 1/4") and an inch or two. <

Think of it this way, the farther you space it off the wall the more low end it will effect and more sound can come in from the sides... Will 1/4" work? Sure, but 2 inches is just better.. Like I said at the start, the way you are thinking of doing it will work, just giving you a way of making it better..
Hope that helps..
Maybe the "master of all acoustics IN THE WORLD" Ethan will chime in.. :) (Sorry guys that is joke Ethan will only understand).

Glenn

Tweakophyte

01-16-06, 11:01 AM

Glenn-

Thanks again for the comments. I wandered around Lowes yesterday and found some glides you put on the bottom of a chair. These are designed to recess into a hollow portion of the chair, so they are 1/2" thick instead of the standard 1/4". From there I am going to add some thick felt (also used for glides) and the net spacing off of the wall should be about 3/4".

Ethan, if you are reading this, for the purpose of letting the sound in from the sides, how much is enough? Is 1/4" too little? How about the 3/4" solution I am looking at?

Because of that additional spacing and the space constraints, I think I'm going with 2"x3" fir for the frames. That should net me about a 1 5/8" air gap for the 2" of rigid fiberglass. Silly question, but does having a non-integer distance as an airgap reduce the effectiveness of the panel? If it does, I can use 3 1/2" MDF, which is a true 3 1/2" and net out to 1/2" of spacing, which would put a 2" gap for the rigid fiberglass.

PS Is "master of all acoustics IN THE WORLD" meant to be read in a monster truck announcers voice? ;)

jponder209

01-17-06, 09:28 AM

I'm planning to build some pannel traps. Is there a way to figure out the sabens for each trap?

John

kwill

01-17-06, 04:50 PM

more bass trap questions:

In my HT room, I have 2 15inch Titanic MKIII subs on opposite sides of the room in the corners. I only have three corners in the room, as one opens into a hallway. This leaves me with one open corner for a large trap, or I could move the subs out from the corners a little and have one large trap, and two smaller traps. I found a local dealer who stocks 2 by 4 foot JM814 (similar to OC 703)
To the questions:

1. Will a trap directly behind the sub (within a few inches) adversely affect it's performance?

2. How exactly does the surface area of the material come into play? It seems to me that a hollow core trap would be less effective than a "superchunk" type. If I took 4 of the 2 inch thick, 2x4 foot panels and cut the material into one foot sections and stacked them in the corner to 64 inches, would this be more, less, or equally as effective as any other configuration with the same amount of material? I am assuming that the low frequency waves, due to their omni directional nature, will enter the center panels in the stack, just as they would the panels on the top and bottom. Is this right?

3. In a stacked corner configuration, is there a need to seal the top and bottom of the traps?

4. Has anyone used bass traps behind Magnepan 1.6 or similar planar speakers? As it is now, one of the subs is just behind the 1.6. If I add a trap to this corner, it will be within three to 3.5 feet of the speaker. Would this be a problem?

I know, the questions are all over the map, but I am really trying to understand this.
Thanks.

bpape

01-17-06, 06:45 PM

No need to seal them.

Bass radiates omnidirectionally so an absorber there should not be a major issue.

Can't say about the Maggies.

As for solid or straddling, the solid has the potential to do a better job down deeper in the frequency range.

When considering where to place bass absorbers, remember that you also have the wall/ceiling horizontal corners that will work pretty much the same as the vertical wall/wall corners. This frees up a LOT more area for you to get the bass under control and also doesn't take up any floorspace and maintains symmetry in the room.

kwill

01-18-06, 03:56 PM

Bpape,

Thanks for the reply.

Can you elaborate on this? "As for solid or straddling, the solid has the potential to do a better job down deeper in the frequency range."

Do you mean that the uncut sheats will work better than stacked one foot sections?
If so, can you explain why?

Tweakophyte

01-19-06, 09:59 AM

Ethan, any additional comments to what Glenn said regarding the spacers I am considering using? (Others are welcome to add, too.)

Thanks,

bpape

01-19-06, 10:05 AM

Ethan Winer

01-19-06, 01:14 PM

dennisgg

01-20-06, 12:50 AM

Hi,

I have a question about bass traps. DIY Network (TV network) had made a Quiktube (4' tall concrete forms in 8:, 10:, and 12" diameters from quikrete company), filled it with sand and put it in the corners for bass traps in their home theater series show. This would be very cost effective to be sure. How effective would this be for a bass trap? Alot of the research I see is using porous ones like fiberglass and a sort of foam rubber. I would really appreciate some help on this. I know that acoustics are a whole science and does'nt have black and white answers, but I would appreciate some guidance on this. Here is the link to their plan:

http://www.diynetwork.com/diy/hi_family_room/article/0,2037,DIY_13912_3471072,00.html

Thank you in advance,

Dennis

bpape

01-20-06, 07:54 AM

This has been discussed before. In short - nobody here or anywhere else I hang out has been able to explain how that would even remotely work. The ONLY thing it MIGHT do is to act as a difffusor - but the diameter isn't large enough to work below maybe 100-150Hz or so.

Somehow, someway, a bass absorber has to absorb bass. It can be thick porous material that turns the waves into heat, it can be a tuned absorber where either an air column or a tuned membrane vibrate at specific frequencies and are damped, or it can be an active system wher the inverse of certain waves is generated out of phase to cancel certain frequencies. It can even be hanging panels that literally move when the waves hit them thereby sucking energy from the wave.

The sand filled tube cannot do any of these things. It won't pass a wave, it has no way to vibrate due to being damped with sand, it can't move due to its mass, and has no air column (damped or not) that can be tuned.

Look for another solution.

Tweakophyte

01-20-06, 09:46 AM

Think about this...

Your two options are:

- Take 2 of the 2'x4' sheets - 2 thick to make 4" - and set them in the corners straddling it at 45 degrees. You now have 8 sq ft of 4" thick absorbtion facing the room with a 15" or so airspace behind it (variable due to the corner).

- Take 3 of the 2'x4' sheets and cut them into triangles (you'll get 8 equal triangles of 1.4' x 1.4' x 2' from each 2'x4' sheet - so 1 sheet will give you 16" of height). Stack them up in the corner. You'll end up with the same size absorber in the corner BUT it will be a solid piece of absorbtion instead of 4" of absorbtion and 15" of airspace. This puts more of the wave and, more importantly, a reasonable part of longer (lower frequency) waves in the absorbtion at any one time.

The solid has the potential to do a better job at lower frequencies albeit at a 50% premium for the cost of the absorbtive material. The cost for mounting and cloth will not change.

Some people do a mix where they make it solid in the upper and lower tri-corners for a foot or 2 and then straddle the 4" in the middle. Also, for the same 3 sheets if you don't want to do all the cutting and making the slats to hold the stack in place, you can just make a 6" thick absorber in a frame straddling the corner. This will also provide an improvement in extension.

Bryan-

Thanks for the comments. I was, infact planning on using 3 pieces for the rear bass traps. I had considered cutting the material into wedges. If I do my math right, isn't it only 4 triangles per sheet? In that case I would need 6 pieces to make it 4' tall. (Did I do that right?)

I wonder if it would be better to do a 6" thick panel, which would be spaced a little further away from the wall (based on the 2' span of the first panel) or do the thicker, wedge-type absorber that is only 2' tall. How about another variation where there outer-most piece of rigid fiberglass is still 2', and you have two more pieces that get thinner. That might be easier to self-contain.

If I interpreted Ethan's paper correctly, it would be surface area and spacing as factors to consider.

Tweakophyte

01-20-06, 09:49 AM

Tweaks,

> Ethan, any additional comments to what Glenn said regarding the spacers I am considering using? <

Not really. 1/4 inch is all but useless. A 6 inch gap is great, but probably more than most people are willing to do.

--Ethan

It sounds like the 3/4" I will end up with is more for looks than for function.

PS... Monster Truck voice? ;)

Thanks again to everyone who supports this thread.

Tweakophyte

01-20-06, 10:00 AM

One more...

Regarding the bass traps in the corner. Is it better to have two 6" thick 4' tall panels straddling the rear corners, or one 4' tall wedge trap in only one corner. How important is symmetry?

Ford Prefect

01-20-06, 10:16 AM

If I do my math right, isn't it only 4 triangles per sheet? In that case I would need 6 pieces to make it 4' tall. (Did I do that right?)

Hi, Tweak. I think Bryan's original math is correct. You will only get four 1.4' x 1.4' squares from a 2' x 4' sheet, but each square yields two triangles, making 8 triangles altogether.

/FP

bpape

01-20-06, 03:58 PM

mmmkam

01-20-06, 04:08 PM

Terry Montlick

01-20-06, 05:41 PM

Accoustically is there any advantage in putting a non-perf screen on a false wall so that linacoustic can be placed on the entire real wall behind it vs putting the screen on the real wall with just linacoustic on the wall around it?
Not under ordinary circumstances, Mike. Special circumstances would include:

Fixing a low-frequency 1/4 wavelength cancellation dip from the front wall. This would typically require a few inches thickness of absorption to be effective at low frequencies.

Deadening early reflections from bi/di-polar or omnidirectional front speakers.

- Terry

dennisgg

01-20-06, 09:17 PM

mmmkam

01-20-06, 10:06 PM

Thanks for the feedback Terry!

Tweakophyte

01-21-06, 09:59 AM

If you cut the sheet in half so you have 2 pcs that are 2x2, then cut those ONCE on the diagonal, you end up with 2 triangles that are 2'x2'x2.8' from each of the 2 pieces for a total of 4.

If you cut the same sheet in half and then cut each of those 2'x2' piecs with an 'X' pattern, you get 4 triangles that are 1.4'x1.4'x2' from each of the 2 pieces for a total of 8.

Either way works, just a matter of how big you want the face of the absorber to be and how much wall space you have.

Doh... Bad math again on my part. I need to wake up before I type some days. (Thanks Ford, too)

I've read about these wedge traps and just assumed you were going for the 2' SIDES instead of the 2' face. I think there was an article these... If I find it I'll link it (and if someone else has it, go ahead an post it).

It still begs the question... for that given volume of rigid fiberglass (three 2'x4'x2") which configuration makes a better bass trap? We can make a 4' tall wedge with a 2' face and continuous thickness to the wall, or a 4' tall, 6" thick panel with a 2' face and variable spacing from the wall.

... and then I will try to stop with the questions... :D

trystan

01-21-06, 02:12 PM

Can anyone comment on this product, vs the fibergalss boards..are they really the same ?
Can the boards be put up without covering them ?

Owens Corning Select Sound Black Acoustic Board

Thanks

bpape

01-21-06, 02:51 PM

Tweak,

It's kind of apples and oranges. When you make 1 16 Sq Ft and 1 8 Sq Ft, you're changing everything. The 4' tall one will absorb deeper but you'll only have half the surface area of bass absorbtion in the room. If you're limited to an either/or situation, I'd go with 4" of fiberglass floor to ceiling since that will also address all of the tri-corners instead of just half of them - and you'll have more surface area in general. The solid thickness is really only helping in the deep bass over 4" straddling a corner.

Dennis - sorry if I came across wrong. No problem repeating the information. When you see something like that from professionals it does make you wonder. I can't see how it would work. I've asked several people who are acoustics pros and none of them thought it would work either.

BasementBob

01-21-06, 03:12 PM

Tweakophyte:

Studiotips Corner Absorber (http://forum.studiotips.com/viewtopic.php?t=534)
Studiotips Corner Chunk (http://forum.studiotips.com/viewtopic.php?t=535)

for that given volume of rigid fiberglass (three 2'x4'x2") which configuration makes a better bass trap? We can make a 4' tall wedge with a 2' face and continuous thickness to the wall, or a 4' tall, 6" thick panel with a 2' face and variable spacing from the wall.If three 2'x4'x2" panels are all the materials you have to build with, I suspect you'll be happier with three Studiotips Corner Absorbers that are 2" thick, 4' tall diagonals with a 2' face. That would give a little less bass absorbtion in the low frequencies per surface ft^2, but probably more sabins of absorbtion in all frequencies including bass for the room.

Megalith

01-21-06, 07:46 PM

Quick bass traps question:

I've got a room that only has one traditional corner where regular bass traps would fit...the rest are tougher since the ceiling is actually angled upwards.

How effective would regular bass traps be in angled corners. If I were to put one in, they'd only be touching the side walls, with the ceiling part open.

bpape

01-22-06, 10:46 AM

Try them in the horizontal corners from side wall to side wall.

fisherman

01-22-06, 03:23 PM

LarryChanin

01-22-06, 04:23 PM

I've read every post on this thread (whew, what a brain spinner) and It didn't seem to answer a fundamental wall treatment type - sheet rock. I've read complaints that it has to be used. Is it the best covering, particulary inside where resonance not isolation is the concern. What is the best covering to attach to the wall studs?

Hi,

By discounting sound isolation you may have inadvertently clouded the issue. Even if you are not concerned about sound getting out of your theater, if you are truly concerned about acoustics then you must logically address sound getting into the theater.

This ultimately gets back to your question of "best". What do you mean by "best"? Many home theater builders are correctly concerned about BOTH the absorption of the walls and their sound isolation properties. Therefore in terms of economics, and reasonably balancing both concerns, starting with drywall walls and treating them (any number of ways) does represent a pretty good alternative to walls constructed of other materials.

For purposes of illustration suppose we follow this reasoning about ignoring isolation to an absurd degree. In such a case we don't need solid walls at all. In such an extreme case we could substitute the appropriate type of fabric walls, and poof, the resonance problems would be solved. ;)

Larry

BasementBob

01-22-06, 06:34 PM

I think of 'best' as good sounding HT room.

'best for individual' involves
a) budget
b) concerns (how close is that noisy furnace!. I don't care if it sounds nice I just want to hear what they say!)
c) local(able) materials.

For materials it's just a question of knowing what they do, and applying them to solve (b) given (a).

Everything (products [gypsum, wood, steel, mineral wool] and systems [walls, rooms, couch]) : transmits, absorbs, and reflects sound to different degrees.

A room is a big system, with lots of these parts.
The pursuit of 'best' room, means using these parts in a combination that results in the best room, givin (a)/(b)/(c).

sheetrock - has mass, and tends to reflect a lot. One layer drywall and no insulation on a flexable wall (G13_WS90(610)_G13) might be soundproof to STC-30 with 20dB TL at 50hz -- and thus let a fair bit of 50hz noise out of the room making it a reasonably effective (higher sabins per ft^2 - it's still an inefficient and uneven and unpredictable absorber as absorbers go but you tend to have A LOT of ft^2 of it) bass centric absorber. Same materials, but combined as a double stud wall, with two layers of drywall and green glue (G16_GG_G16_WS90(610)_GFB90_AIR25_WS90(610)_GFB90_G16_GG_G16 ), might be soundproof to STC-71 with 30dB TL at 50hz -- this wall reflects a lot more of the sound back into the room (real lousy absorber because it's WAY innefficient at absorbtion).

fiberglass, rockwool, acoustic cotton, decent foam, polyester: much better at absorbtion than drywall. Leaps and bounds better at absorbtion than drywall. Placement affects its absorbtion rate at various frequencies (diagonal corner placement boosts LF absorbtion a lot extending its broadband absorbtion)

Too much HF absorbtion in the room and you want more LF absorbtion -- cover what you've got:
a) 100micrometer PVC foil - reflects HF, lets LF through it.
b) slats
c) membrane or helmholtz

Have an annoying reflection producing comb filtering or imaging problems, but you already have too much absorbtion at all frequencies -- consider diffusion to scatter/reduce one of the reflections. Sound reflecting off something causing a problem, how about a twist poly. The walls themselves are good reflectors, as are cabinets. Cabinets can block a reflection - or move it a bit.

You want speach inteligibility (low background noise, few early reflections, masking, FR, distortion, time), and ambiance and spaciousness -- these are a blancing act -- that combine everything the room is made of, from the walls, to the carpet, to the couch, and everything else.

A friend of mine bought a HomeTheatre-In-A-Box with 10" LCD screen for his 8 year old son. Who promptly took it into his bedroom where he has built (leaned and tied with rope) a few 4'x4' sheets of plywood into a sort of 'fort' in the corner of the room. Set the HTIB up inside the 'fort' and watched Bambi. He bragged about it to all his friends. "It's just the best!" The 8 year old had (a) no budget, (b) extremely good hearing, and (c) local is defined as what's under the christmas tree and what's in the garage. I understand the neighbour's 'fort' occupant is jelous.

fisherman

01-22-06, 07:53 PM

I see how I left the interpretation I was discounting isolation. To clarify, I have found lots of information on isolation. For my DIY theater in progress I'll be using QRock 545 THX with RSIC-1. Also, by best I mean what the major knowledgeable AVS members would say about: 'this is the way to go about no bad seat in a HT'.

What is not clear is reflected in the points made by both and BasementBob and LarryChanin "Everything (products [gypsum, wood, steel, mineral wool] and systems [walls, rooms, couch]): transmits, absorbs, and reflects sound to different degrees" and LarryChanin “For purposes of illustration suppose we follow this reasoning about ignoring isolation to an absurd degree. In such a case we don't need solid walls at all. In such an extreme case we could substitute the appropriate type of fabric walls, and poof, the resonance problems would be solved” Why do we need drywall (besides cheap and available).

It seems by trying to understand all members’ advice; you all have a ‘best practice’ in mind. What is that best practice for inside covering once you have isolation – no sound in, no sound out - accomplished

You’re needed for you for you mind not you’re …… ;)

jandawil

01-23-06, 09:18 PM

Hey everyone....I found a dealer close by that exclusively deals in Roxul mineral wool and their prices are very good. I am planning on doing corner bass traps in the rear 2 corners of my HT and will cut 4" thick wool into triangles with a 2' face and they will go 12" deep into the corners. If my math is correct I can get 8 triangles out of a 24'X 48" sheet and at 4" thickness one sheet will get me 2' high. Their price is about $19.00 for 24 sq feet (4 24"X48" sheets) so that will give me 8' high corner traps for less than $20 each!!! That sounds very reasonable. I often hear of people spending far more than that. Am I missing something??

Also since they do not carry rigid fiberglass, I am limited to 1 1/2" mineral wool for sound panels for my early reflection points on the side walls. Has anyone used this for that purpose?? Is it rigid enough to simply cover in a fabric and hang it on a wall?? Will I need some sort of backing or frame to support it?? Any experience out there would be greatly appreciated.

Thanks a bunch.....

bpape

01-24-06, 12:07 PM

Jon,

Yes. You can get 8 1.4 x 1.4 x 2' triangles from a single 2'x4' piece. Each piece being 4" thick will yield 32" vertical inches of solid triangle from a single sheet. So from 24 Sq Ft, you can get 96" vertically or 8'. For clarity, 24 Sq Ft is 3 sheets, not 4 - each is 8 sq ft. Just make sure of the density of the material. That's a very good price if it's 8lb/cu ft.

As for the refleciton panels, if you can get a lighter density - like around 3-4 lb/cu ft. If it's all 8lb, I'd look at something different as those are too dense IMO.

jandawil

01-24-06, 12:52 PM

mccabem

01-25-06, 11:51 PM

myfipie

01-26-06, 07:43 AM

Just jumping in here with a question relating to putting carpet on the walls. From what I've read on this thread, I obviously need to put absortion material below ear level. Most likely I'll just go the entire length of the room or at least the distance from screen wall to seating instead of trying to figure out the point of reflections and putting absorbing panels at that point.

My question is with the upper portion of the wall. Can I cover the sheetrock with a real tight woven carpet? I want to do this so I don't have to build a lot of frames and cover with GOM and I don't really have the sheetrock finishing skills to just paint it either?

Any good or bad characteristics of carpeting the upper half of my side walls?

If this has been previously addressed elsewhere, please direct me to that thread.

Thanks,
Matt

You do not want to put carpet on the walls.. It is only going to help with the high end and leave the low end bouncing around the room.. The low end is the biggest problem areas in rooms. Stick with rigid fiberglass panels on first reflections and bass traps in the corners... Bass traps should be 4" thick and first reflection panels should be 2 " thick..

Glenn

bpape

01-26-06, 09:29 AM

Jon.

The 4.5lb will work. If you want it a bit better at lower frequencies, you can use 6" to compensate somewhat for the lower density.

mccabem

01-27-06, 01:23 PM

myfipie

01-28-06, 07:42 AM

Glenn,

Thanks for your reply. To clarify, is the carpet going to absorb too much of the mids/highs and cause the room to sound dead?

I plan to use the fiberglass insulation below ear level and just have concerns with the material above the ear, no carpet below ear leve.

Thanks,
Matt

Sounds like to me you are going to have way to much HF absorption.. I am not going to say it will go dead, because of type of carpet and so on, but carpet is really not recommend for acoustic treatment.. For the upper wall it would be best to straddle 4" panels in the corner where the wall meets the ceiling.. That will act as a bass trap..

Glenn

Tweakophyte

01-28-06, 09:33 AM

...just thought I would lay this out in case I had confused anyone.

Tweakophyte:

Studiotips Corner Absorber (http://forum.studiotips.com/viewtopic.php?t=534)
Studiotips Corner Chunk (http://forum.studiotips.com/viewtopic.php?t=535)

If three 2'x4'x2" panels are all the materials you have to build with, I suspect you'll be happier with three Studiotips Corner Absorbers that are 2" thick, 4' tall diagonals with a 2' face. That would give a little less bass absorbtion in the low frequencies per surface ft^2, but probably more sabins of absorbtion in all frequencies including bass for the room.

Thanks (again) for the links. I can clarify what I was trying to describe for my options. This is what I said Is it better to have two 6" thick 4' tall panels straddling the rear corners, or one 4' tall wedge trap in only one corner.

Studiotips Corner Absorber (http://forum.studiotips.com/viewtopic.php?t=534) is what I am describing when I said "a 4' tall, 6" thick panel with a 2' face and variable spacing from the wall " and "two 6" thick 4' tall panels straddling the rear corners" In this case the Studiotips corner absorber is suggesting at least 4" thick (I am looking at 6"). They also suggest adding some additional fiberglass behind the panel that is straddling the wall, by tucking in an additional piece of OC703 into the corner itself.

Studiotips Corner Chunk (http://forum.studiotips.com/viewtopic.php?t=535) is what I meant when I said "wedge trap". There are two cutting patterns: one for a 24" face (8 wedges per piece of rigid fiberglass) and one for a 34" face (4 wedges per piece of rigid fiberglass).

Unfortunately the only measured the 4" thick "corner absorber" compared to a 34" face "corner chunk" aka "Super Chunk". Neither are the options I am considering since I am looking at a 6" thick "corner absorber" (with a 24" face) compared to a 24" faced "corner chunk". The comparison would be neat because they use the same amount of material.

My current thought is to make a corner absorber, 4-6" thick for ease of construction and portability if the WAF becomes a factor. If I want to improve the performance of that, in the future I can add "fluffy" insulation, or other material behind the corner absorber to improve the bass trapping performance.

Thanks again.

stef2

01-29-06, 11:19 AM

Hi everyone. I've been following this thread for a while and a few details about sound treatment remain unclear to me. Would anyone be kind enough to enlighten me?

1- I am about to finish drywalling my home theater and I still have the possibility to change the dimensions of my room when I'll build a faux wall for my screen. My room's dimensions would be 141 inches wide by 93 inches high by 242 inches long. This is close to a 1:1,5:2,5 ratio. Is this a good room size ratio? The dimension that I could modify is the lenght. Any suggestions?

2 - My second question is about corner bass traps. Considering a constant dimension and using the same materials, is it better to completely fill the corner or to leave an air gap behind the fiberglass panels ? (My corner traps would be triangular with a diagonal of 2 feet and I plan to use OC703 for those)

3 - And at last...Centered in the wall behind my (non perforated) screen there is a recess about the three feet wide and two feet deep that goes from the floor to the ceiling. It was intended for a fireplace and its chimney. What should I do with this? I thought about filling it with insulation and leaving it in contact with the room using GOM. But since this "shape" is directly behind the screen, should I just make it disappear by running drywall in front of it, making the front screenwall completely linear? If so I would probably also fill the cavity to avoid creating a Huge drum...

Thanks in advance for your precious feedback!

Ethan Winer

01-29-06, 11:45 AM

Stef,

> This is close to a 1:1,5:2,5 ratio. Is this a good room size ratio? <

Yes.

> is it better to completely fill the corner <

Yes, but only marginally better.

> It was intended for a fireplace and its chimney. What should I do with this? <

Fill it with fluffy fiberglass and you'll get some useful bass trapping.

--Ethan

Ready2Buy

01-29-06, 05:45 PM

Hi all,

I just discovered this thread and let me say that I am very impressed with the quality of the content and the many excellent contributions made by the acoustics experts here. It is really a joy to come across this jem.

I too am one of those with limited DIY skills and limited budget who is trying to transform an EXISTING room in our home to a home theater. (Yes I too got infected by the “bug”.) Already bought the 7.1 speakers (actually the ".1" has not been bought yet), the receiver/amp, the DVD player and the Radioshack digital SPL meter. The new objective is to improve the room acoustics with the simplest possible design and the least amount of labor.

With that said I have to second BasementBob’s view that one of the most important issues facing the DIYer is the availability of materials in his local area. For example, I live in Los Angeles and after already calling eight different insulation suppliers in my area I found that none of them has the 4” thick fiberglass boards for sale. Some of them don’t even carry any fiberglass rigid board insulation at all. BTW, if anybody in this forum knows where to get 4” thick boards anywhere near Los Angeles please tell me. I am willing to drive up to 100 miles from downtown.

The best I was able to locate in my area are 2” thick boards:

(1) JM-IS300: Cost $79 for nine 2”x2x4 boards per bundle ($1.10 per sq.ft.)
(2) JM-814: Cost $122 for only six 2”x2x4 boards per bundle ($2.54 per sq.ft.)
(3) OC-703: Cost $76 for ten 2”x2x4 boards per bundle ($0.95 per sq.ft.)

The absorption coefficients (from bobgolds.com) for 2” JM-IS300 and 2” JM-814 are identical and both are a little better at low frequency than the 2” unfaced OC-703. Obviously the best deal is the OC-703 if cost per unit is the only factor. However, considering that the above three suppliers are 15 miles 35 miles and 75 miles away from my house it appears that the JM-IS300 is my best option.

So I have two questions for the bass trap experts and those who have already done a fair amount of thinking on this subject.

First is the JM-IS300 2”-thick a good material to build bass traps? Or should I continue to look for other materials or thickness?

Second, I have come up with a simple design to make these and would like to invite comments from this forum. In fact this design is so simple that I am even embarrassed to describe it. It doesn’t require any cutting of the fiberglass (we know this material is unpleasant to work with) and it doesn’t require that I build a frame of any kind. What it does require is a lot of panels. Here it is:

At each of the 4 corners in the room I will use twenty-four 2”x2’x4’ panels as follows. Stack 12 2”x2’x4 panels together creating a 2’x2’x4’ solid shape. Wrap it like a Christmas gift using speaker fabric (Joann’s fabrics has it for $6/yard) and then stand it up in the corner. Build another one just like the first one and stand up on top of the first one. This is now a 2’x2’x8’ square pillar placed against the walls into the corner of the room. Repeat this process three more times to block all four of the room’s corners and you are done. These “square pillars” are free-standing and do not require a frame. To pull this off in all four corners I will need a total of 4x24=96 2”x2’x4’ boards. This will cost me about $850 for the fiberglass alone but should work great! This design should be even more effective than the prismatic Superchunks design Bob mentioned with the 34” exposed face as my “square pillars” will have an even larger 48” (2 faces of 24” each) exposed into the sound field of the room.

Please comment on the effectiveness of this extremely simple design. Of course I would rather have the 4” thick boards so that I spend a bit less for fiberglass but I can’t find any at the moment. Yes I know that I am using too much fiber but the simplicity of the design outweighs having to get cute with the framing and the wrapping issues.

Thanks again to everyone contributing to this thread. It’s a real asset for those of us who are DIY-challenged and have a limited budget that doesn’t allow for purchasing the good stuff (i.e., realtraps, megalenrds, tubetraps etc.) but still want to reach deep down and damp those low frequency acoustic waves.

John

Terry Montlick

01-29-06, 06:12 PM

Design looks good, John. JM-IS300 is just as good as any other fiberglass. You can ignore small differenced in published absorption coefficients of fiberglass, particularly at low frequencies. It is just measurement error. Just go by the density, and all of these are 3 pcf.

It’s a real asset for those of us who are DIY-challenged and have a limited budget that doesn’t allow for purchasing the good stuff (i.e., realtraps, megalenrds, tubetraps etc.) but still want to reach deep down and damp those low frequency acoustic waves.

You are building the good stuff!! There is no difference between acoustical treatments bought ready-made with cash or with sweat equity.

- Terry

Ready2Buy

01-30-06, 01:05 AM

You are building the good stuff!! There is no difference between acoustical treatments bought ready-made with cash or with sweat equity.

- Terry

I appreciate this Terry. The only other question I have on these materials has to do with the health risk issue (if there is one). I see a number of posts that mention that fiberglass materials either cause cancer or that they are generally unhealthy to be around. I have also seen an equal number of posts disputing these claims. I understand that we have to wrap these panels possibly twice with polyester batting and then again with a nicer looking breathable fabric. But is this enough for these panels to not interfere with our health? I mean do we know of anybody who got sick or developed respiratory problems from having too many panels in his room?

Also do we know how the different fiberglass brands compare on the health issue? Is for example the JM-IS300 material "healthier" to have inside your room than the OC-703 material? Or are they all pretty much the same health-wise?

John

JamesE

01-30-06, 06:49 AM

At each of the 4 corners in the room I will use twenty-four 2”x2’x4’ panels as follows. Stack 12 2”x2’x4 panels together creating a 2’x2’x4’ solid shape. Wrap it like a Christmas gift using speaker fabric (Joann’s fabrics has it for $6/yard) and then stand it up in the corner. Build another one just like the first one and stand up on top of the first one. This is now a 2’x2’x8’ square pillar placed against the walls into the corner of the room. Repeat this process three more times to block all four of the room’s corners and you are done. These “square pillars” are free-standing and do not require a frame. To pull this off in all four corners I will need a total of 4x24=96 2”x2’x4’ boards. This will cost me about $850 for the fiberglass alone but should work great! This design should be even more effective than the prismatic Superchunks design Bob mentioned with the 34” exposed face as my “square pillars” will have an even larger 48” (2 faces of 24” each) exposed into the sound field of the room.

John

This is a brilliant idea. Fill the blocks with regular fiberglass insulation for added low end absorbtion and buy yourself "The Master Handbook of Acoustics" to fill in the gaps of information on this forum. Although, this forum is pretty hard to beat.

Tweakophyte

01-30-06, 08:56 AM

Terry Montlick

01-30-06, 09:57 AM

I appreciate this Terry. The only other question I have on these materials has to do with the health risk issue (if there is one). I see a number of posts that mention that fiberglass materials either cause cancer or that they are generally unhealthy to be around. I have also seen an equal number of posts disputing these claims. I understand that we have to wrap these panels possibly twice with polyester batting and then again with a nicer looking breathable fabric. But is this enough for these panels to not interfere with our health? I mean do we know of anybody who got sick or developed respiratory problems from having too many panels in his room?

Also do we know how the different fiberglass brands compare on the health issue? Is for example the JM-IS300 material "healthier" to have inside your room than the OC-703 material? Or are they all pretty much the same health-wise?

John
The fibers are contained by the fabric. They do not float in the air to be breathed. Future research may turn up health risks for people (nothing so far), but I believe that any such risk would be confined to installation, and dealt with by wearing a dust mask.

- Terry

Ready2Buy

01-30-06, 04:36 PM

John-

I don't know if you saw that I took 5 peices of JM-814 that were in a bag and stuck them in one corner for a quick a/b. I experience a HUGE difference in frequency response. I played a techno tune that has a lot of long, reverse, bass sweeps. This normally exposes all the ups and downs of the FR. The simple bag in the room trick was instant validation.

Did you just stand them up into the corner in the shape of a box 4' high trapped between the 2 walls of a corner? At 2" thick and using 5 boards you have built a 10"x2'x4' solid rectangular absorber. I am surprised that you notice such a big difference in your music with only 5 panels of material and in only one corner of your room.

Have anybody done a study in how to best place these panels in a room? I mean given a a specific number of panels (say 96 2"-thick panels) would you stack 24 in each of the 4 corners and be done? Or would you try to maximize exposed area by sacrificing the thickness of the material in the 4 corners of the room?

What would help greatly here is an acoustic model of an empty room with the ability to add rectangular absorption panels all around the corners and predict the resulting sound field. The user would enter the dimensions of his room and proceed to place 2'x4' panels at various locations (that only he knows is allowable) until the right number and the right placement emerges that satisfies his sound requirements. Obviously I am dreaming here but hey why not? This would definitely be worth a "sticky" :)

Kal Rubinson

01-30-06, 04:52 PM

Take a look at CARA 2.1. You can put almost anything in to the model.
http://www.rhintek.com/cara/cara21desc.php

Kal

Ready2Buy

02-01-06, 03:47 PM

I am now the proud owner of 63 JM-IS300 2" 2x4 boards. All for $500 and I cleaned out the guy's stock!

I was speaking to another fellow on the net about making these 2'x2'x8' square pillars and he suggested that I don't lean them against the corners because the velocity of the acoustic waves on the wall is zero and they wouldn't be very effective. He instead suggested that I space them 6" away from both walls to gain even more effectiveness down low.

If I were to do that I would probably have to make a rectangular frame for them to gain more stability to stand up straight and then attach the fabric to the wood frame instead of gluing it directly on the panels. It's a bit more effort to build it but because its a simple square frame I think I can give it a try.

My question is, does spacing a 2'x2'x8' fiberglass tower 6" away from both corner walls really gain you anything as compared to having it resting directly on the walls? (My room is 20'x20'x8' and has a pair of modes at 28 Hz and then again at 56 Hz.)

John

bpape

02-01-06, 04:06 PM

Ready2Buy

02-01-06, 05:07 PM

You'd be just as well off to make them 6" thick and put them up straddling the vertical room corners at 45 degrees. That gives you MORE distance from the boundary and gives you extra thickness for even better control down low. Doing all 4 corners this way will still cover 1.4'x8' on each of the wall surfaces and only use up 24 of the 2" panels.

Bryan

Hmmm, thanks for the reply. I read somewhere in an Ethan Winer article that you need to "trap" a quarter of the wavelength of sound for maximum absorption but even if you trap 1/8 of the wavelength will also give good results. I got modes down at 28 Hz whose wavelength is 40 feet long so to trap even 1/8 of that I would need 5-foot thick panels. I am using 2' panels wich means I am trapping a mere 1/20 wavelength at this frequency which is probably not enough. Why would a mere 6" spaced off the wall work just as good as 2'-thick bricks? At a frequency of 28 Hz? I am confused ...

John

Brock225

02-01-06, 06:26 PM

First of many questions to come. In making diagonal bass traps for corners, should the surface facing the room have a paper, vinyl or foil facing on it under the fabric to allow low frequency and not higher frequency sound waves to be absorbed.
I have subs in the back 2 corners of the room. Do I ignore any bass trap of any kind at the back of the room?

Brad

Glenn Baumann

02-01-06, 08:04 PM

Brad,

I believe the conventional wisdom is that all corners are valid and effective. Treatment is also very effective at not only the wall-wall corners as in your case but at the wall-ceilng and wall-floor junctures as well. I have also read that the juncture where two walls and the ceiling corner meets is another very effective absorption spot, this being the tri-corner. :)

...Glenn

Stima

02-02-06, 12:12 AM

First, let me THANK YOU for reading this long post and helping me out. You will receive many rewards in heaven for your good deeds!! :D

As it seems with many others I have reached the Acoustical Treatment phase so I turn to the experts here for opinions.

Background:
Room is essentially rectangular (11' wide x 16' long x 8' high (height varies over rear riser and front mini-stage).

Seating is at 11' and 14'. (Riser is 10" high)

Whats odd about my room is the front has a "half-hexagon" extension for a bay window above.

I plan to put an acoustically transparent screen and wall at the beginning of this hexagon extension to visually square off the room. Speakers will be mounted behind the wall. The room has a thick berber carpet, and I don't have any plans to treat the ceiling with AT. (I will treat the undersides of the lighting softis however with 703).

I am not extremely worried about bass leaving the theater. However, I did build separate floating walls and a ceiling. I decided to only do a single layer of Drywall rather than "beef" them up with GG and a second layer. I did this to allow the walls\ceiling to absorb bass rather then reflect it into the room. Also, I filled the void between the two walls and ceiling\floor with fiberglass.

More Background:
Went and visited Dennis E.'s 2.35:1 theater for advice and he suggested I do the following:
Put 703 from floor to ceiling on the "extension walls" all the way to the first listening position.
Cover approximately half the remaining walls with 703.
Cut faux AC vents into my riser and shove batting into the cavities to utilize it as a base trap.
Tear down the drywall from my front wall (now acoustically transparent) and go with a 2.35:1 setup placing all speakers behind the AT screen\wall.

Questions:
1.) My riser is formed by 12 square areas approximately 16"x 24". How many (if any) of these areas should I make into bass traps?
2.) Should I utilize the large area behind the screen for bass trapping since it will be hidden and won't affect the cosmetics of the room?
3.) Putting 703 from floor to ear height is an approximation mainly for amount of 703, not position. Therefore, I can put panels in the "middle" of the remaining walls surrounded by batting. Correct?
4.) Finally, was my thought process with the single layered walls\ceiling completely inaccurate? I only ask this because I still have the opportunity to put a second layer on the walls before I put acoustical treatments up. (A second layer on the ceiling would be very difficult now given lighting and painting is completed.) More pertenant: Is there even any reason to add this second layer to the walls since the ceiling is single layered?

Hope that wasn't to many questions.

I REALLY do appreciate any help and will carefully consider any suggestions. (I already am tearing down the permanent wall I WAS going to use to "visually square" off the room per Dennis's suggestion.)

Thanks,
Dan

BasementBob

02-02-06, 01:08 AM

Ready2Buy:

the velocity of the acoustic waves on the wall is zero That's not quite true.

Sound going straight towards a wall, will have it's velocity drop to zero and pressure go up at the wall surface.
See "Reflection of a sound wave at a hard wall"
at http://www.isvr.soton.ac.uk/SPCG/Tutorial/Tutorial/Tutorial_files/Web-inter-reflex.htm

Think of a swiming pool. Make a splash (wave) on the surface, and the wave goes towards the wall, goes up the wall (stops velocity at the wall as the wall changes the wave from horizontal velocity to vertical potential energy), reflects, and returns.

But sound going along the wall (parallel to it), doesn't convert velocity to pressure -- it stays as velocity.

Think of a river, or a water pipe, certainly water flows along the 'walls'.
Think of a swimming pool, you've seen waves traveling along walls of a swimming pool (both parallel and at angles).

Tweakophyte

02-02-06, 09:15 AM

Bob-

Great clarification. I guess it's more common than not that the sound "splashes" versus bounces straight back (which would cause it to go to zero). This also highlights why tri-corners are a great place to focus.

Ready2Buy

02-02-06, 11:04 AM

Ready2Buy:

That's not quite true.

Sound going straight towards a wall, will have it's velocity drop to zero and pressure go up at the wall

Hi Bob,

I think I understand the swimming pool analogy but it still doesn't explain to me why people get more damping out of their panels when they space them several inches away from the wall versus placing them directly against the wall. Reading these forums there are countless statements from experts pointing out that large airgaps between the panels and walls somehow increase the absorption of sound while using the same amount of fiberglass material. And they have measurements to prove this. The only explanation I was able to glean from what I read had to do with the wave velocity being zero at the wall.

But why would a 6"x24"x96" fiberglass panel placed diagonally in the corner of the room give about the same performance as a 24"x24"x96" fiberglass brick placed in the corner? Bpape's opinion is that you will probably get about the same damping out of both even if you spaced the 24"x24"x96" brick 6" out from the corner. I am trying to understand why this would be right because it stands against the basics physics of sound I thought I knew. If he is right, then there must be some fundamental limit of absorption that, once we reach it, adding more fiberglass will not bring more dividends. Is this what it is?

(My room is pretty square 20'x20'x8' without any openings and I've got double modes at 28 and 56 Hz. That's why I went out amd bought all these fiberglass boards. I thought the more boards the better. )

John

bpape

02-02-06, 11:21 AM

Ready2Buy

02-02-06, 04:16 PM

John,

OPTIMAL is to get the wave at a quarter wavelength from the wall. This does not mean that you can't be effetive at other places. This does however explain why spacing panels off the wall helps - you're getting closer to longer waves' 1/4 length spacing from the wall.

There are several things that control how deep an absorber will reach effectively.
- Thickness (more of the wave in absorbtion at any time and more absorbtion to slow things down in general)
- Density (slow down larger waves more per inch of thickness)
- Distance from the wall - see above.

You have a lot of stock to work with - use it wisely. As I said previously, make the absorbers 6" thick. This gets the leading edge of the absorbtion farther from the wall (see #3 above) and also give you more thickness for the same density material (see #1 above).

Adding more SURFACE AREA will still increase absorbtion. The problem is that you can get to a point where OTHER frequencies are now too damped. The idea is to bring the decay time in the room down to an even balance across the whole spectrum. Some things in the room are already doing absorbing.
-air
-carpet
-people
-furniture
-drywall walls

The trick is to know what they've all done so far and then see where you stand in relation to the target time for your particular room size and usage.

I am with you. So to summarize, the three keys to building good bass traps using fiberglass are

1. Panel Thickness
2. Panel Density
3. Spacing from wall

With regards to the first key point, I have now bought so much fiberglass material that I can make pretty much any thickness from 2" all the way to 24". I think everyone seems to agree that the thicker we make'em the better the result. (Does anyone disagree on this point?)

With reqard to panel density, I am pretty much stuck with the 3 pounds-per-cubic-foot matrial due to local availability (JM-IS300).

The third key point however, is the most difficult to interprete because it addressses the PLACEMENT issue. The best placement requires that we accept a larger reduction in our usefull room space and placing the traps really far from the walls.

In my case, I am under the constraint of not wanting to dedicate more than 6 square feet per corner trap (or 24 square feet for four) from the 400 square feet available in this 20'x20' room. (That's about 6% of the total area of the room going to the corner treatments). If I were to go with traps that straddle the corners diagonally as you suggest I would at least use 10" thick ones (using five 2"-thick panels one behind the other). These traps would still fall inside a 24"x24" corner envelope wasting about 4 square feet of space per corner (16 sq. ft. total) of my room. To pull this off I would have to use a total of 40 panels for all four corners which would leave me with the remaining 23 panels to treat first reflections. Hmmm, I may have bought too many :(

The problem you mentioned about overdoing it by absorbing too much of the mid and high frequencies has me worried however. I bought this many panels because I though I was going to use most in the corners and was going by what Ethan said in a previous correspondence, i.e., "you can't have too many bass traps".

(At first I thought this was not too hard to figure out, now I am not so sure ...)

myfipie

02-02-06, 07:10 PM

Brock225

02-02-06, 07:45 PM

On first reflections using a mirror would the following affect dampening material on side walls. My main L&R are toed in approx. 18 degrees, 9 ft. apart and 15 ft in front of me. Do I need to make any adjustment for the fact that (this is an assumption I am making) the sound waves would hit closer to me on the side wall even though I see the speaker in the mirror? I see more of the side of the speaker than if it was facing straight forward. Is this nothing to be concerned about or does it depend on the disperion pattern of the Martin Logan SL3's.

Stima

02-02-06, 07:54 PM

Anyone have opinions on my few questions? :o

ebr

02-02-06, 08:04 PM

Ready2Buy

02-03-06, 12:44 AM

If you put some FRK on your bass trap panels you would be fine.. That should keep the room alive... Not making it dead but absorbing the low end.. But for the first reflections you should not use the FRK... I can't see needing 23 panels for first reflection points..

Glenn

Hi Glenn,

Instead of FRK how bout using a less breathable fabric? I don't know where to get FRK but I can certainly get some nice upholstery fabric which is not as air-transparent as burlap or GoM. I could use that to wrap the panels instead of speaker cloth.

This should help by removing less of the high frequencies and not over-deadening the room, yes?

Stima

02-03-06, 02:07 AM

Stima - I'm afraid you are getting into some things that are very specific to your room so the answers to your questions are going to be "it depends..."

You have to realize most of the true experts who contribute out here solve the very detailed problems you are asking about for (at least some part) of their living. So, it may be very difficult to get complete answers to your questions in this forum. If you really want to be sure you do this right, I would suggest contacting one of these guys and talking to them about providing you with specific service.

Now, that being said - someone like Bryan or Terry or Ethan may jump in here and help you out at least to some extent. I am continually amazed at the amount of time, effort, and advice these guys lay out here for free.

I was afraid to list all my basement spec's for the very reason you mention. However I always seem to find the no-win situation on forums. If I ask for help, it seems I am always not giving enough info or giving to much. :confused:

Perhaps, If I simply had written my initial post as follows, people (anyone) would reply:

What is the final concensus on OC703 placement as absorption?
What do people suggest for using a riser as a bass trap?
Can bass traps go behind a screen?

:confused: :confused: :confused: :confused:

BasementBob

02-03-06, 06:35 AM

OPTIMAL is to get the wave at a quarter wavelength from the wall. This does not mean that you can't be effetive at other places. This does however explain why spacing panels off the wall helps - you're getting closer to longer waves' 1/4 length spacing from the wall.
Close.
Porous absorbers are velocity absorbers -- they absorb the most where the wave is moving the fastest. Spacing them off the wall does extend lower frequency absorbtion for the same cost in material.
For a sine wave the highest velocity is at the 1/4 and 3/4 wavelength points.
But
a) most sound doesn't go straight into a wall, so 1/4 wavelength out from the wall is just about meaningless. With 7 speakers, best case is 1/7th of the direct sound is hitting one spot on one wall straight into it. The rest is hitting at some angle. And after a few milliseconds all of the reverberant field can probably be considered fairly diffuse (all angles). Although the rear wall, relative to the front center speaker, might apply to this 1/4 wavelength (not a diffuse absorbtion test like those at http://www.bobgolds.com/AbsorptionCoefficients.htm), certainly all the sound hitting the first reflection point absorbers wouldn't be going straight-in-and-straight-out from the fronts because it's all hitting at an angle.
b) most sound isn't a sine wave, thus it probably doesn't have its maximum velocity at 1/4 wavelength
c) Just because the absorber is most efficient at the highest velocity part of the wave (1/4 wavelength for a sine wave), that doesn't mean it doesn't still work well at lower frequencies. As long as the air is moving it still works, just to a lesser degree. 701 plain 1" on wall has a 0.17 absorbtion coefficient at 125hz, even though 1" 1/4 wavelength would be 3390hz.
d) I think that most sound is travelling wave (as opposed to standing) may be relevent too.

There are several things that control how deep an absorber will reach effectively.
... - Density (slow down larger waves more per inch of thickness)Density is not a guarantee that it will work better at lower frequencies. There's not a lot of dependable lab work at under 100hz. One thing that higher density is known to do is reflect high angles of incidence for higher freqeuncy sound -- thus high density shouldn't be used for first reflection point absorbers, although you might try it on the rear wall.

Normal vs Grazing incidence (http://www.bobgolds.com/NormalVsGrazing.GIF)

The idea is to bring the decay time in the room down to an even balance across the whole spectrum. Actually the best thing to do is to match the DVD recording engineer's RT60 spectrum, but that's impossible. Jeff of Auralex fame has done thousands of rooms, and he managed to get about two of them +-3db from 100hz to 8000hz. A little extra in the bass is apparently ok.

This is a pretty good comparison of absorbtion between
a) 4cm on the wall
b) 4cm, with a 4cm space behind it
c) 8cm on the wall
Theoretical Effect of Moving an absorber out from the wall (http://www.bobgolds.com/absorbtion%20Porous_Absorber_&amp_xls%204cm%20of%205.00%20kPasPERm2.GIF)

Note how absorbers flat parallel to the wall tend to absorb a lot of HF, but little LF, and it's pretty much a gentle slope between them with no peaks (other than the right hand side).
A lot of things you're likely to have in your HT, like carpet, have this absorbtion trend.

A corner absorber has an absorbtion curve like this
Studiotips Corner (http://www.bobgolds.com/StudioTipsCornerAbsorbtion.gif)
Note how its got a peak of absorbtion near 100hz, and the higher frequencies are relatively lower absorbtion.
This is one of the few (only?) porous things that have a different absorbtion trend.

That should keep the room aliveActually you want the room to be fairly dead. Not anechoic chamber dead, but certainly not 'live'.

vinyl

02-03-06, 06:53 AM

Actually you want the room to be fairly dead. Not anechoic chamber dead, but certainly not 'live'.

Great post Bob - The above statement couldn’t be truer for HT.

Tweakophyte

02-03-06, 09:21 AM

Hi Bob-

Was that corner chunk profile pulled from a thread? Is that "corner chunk" the version with the 24" face, or the "super chunk" with the 34" face (both are called "corner chunk" from what I can tell.

I am still wonder what the best bass trapping configuration is for 3 pieces rigid fiberglass... 6" thick corner trap or corner chunk with a 24" face. I could not find a direct comparison in the links you helped me with (only the "super chunk" vs corner trap).

Also, based on that normal vesus grazing pic you posted, it seems you should cover first reflection panels made with OC703 with something fluffier to improve the high-frequency absorbtion profile.

Stima

02-03-06, 09:47 AM

Just wanted to say thanks to -BB- for the PM. :cool:

I will do some more reading\research and then re-post. ;)

bpape

02-03-06, 01:32 PM

Off to a meeting pretty quick - will try to post some answers later.

Bryan

BasementBob

02-03-06, 06:14 PM

Tweakophyte:

Was that corner chunk profile pulled from a thread? Is that "corner chunk" the version with the 24" face, or the "super chunk" with the 34" face (both are called "corner chunk" from what I can tell.You might have noticed that there are no numbers on the vertical axis called "absorbtion". So basically I meant all of them. I was speaking more of trends than actual absorbtion coefficients. (That said, the data I used to make the graph was from the 24" face with 4" material Studiotips Corner Absorber.)

I am still wonder what the best bass trapping configuration is for 3 pieces rigid fiberglass... 6" thick corner trap or corner chunk with a 24" face. I could not find a direct comparison in the links you helped me with (only the "super chunk" vs corner trap).That sounds like "Hi doctor, I'm an 18 year old olympic athlete. I found these two containers of pills on the ground. This bottle says it's to be taken during a stroke to reduce future problems, and this bottle says it's to be injected during a heart attack. Which should I take every day?"

It's called acoustic treatment.

Isn't it better to start with an acoustic problem you're trying to solve, and then build treatment that corresponds to the problem, and then measure before and after to see if its actually done what it was supposed to?

6" thick corner trap or corner chunk with a 24" faceI believe you mean that both would have a 24" face, one is full of fiberglass, and the other has an airspace behind it. And those are compared at studiotips (4" with airspace and 24" face, vs full of fiberglass chunk with 34" face) (http://forum.studiotips.com/viewtopic.php?t=536).

The short answer about the 'difference' between two with a 24" face, one full and the other with 6" of fiberglass and air behind, is not much. From 200hz and up they'd probably be identical. From 63hz and below the chunk that is full would probably have significantly more sabins of absorbtion. Between 63hz and 200hz I'm not sure, but I'd bet that the full one would have a bit more absorbtion.

The question "which is the best absorber" is the wrong question to ask. If you have a room that's acoustically perfect, then adding Auralex MegaLENRDs would be a bad thing. If your immediate problem is flutter, then corner traps are a waste of money. If the problem is a floor ceiling mode, then placing absorbtion on the walls probably isn't going to help. If it's an imaging problem caused by SBIR, then ceilingwall traps aren't going to help. The question is either "what's the complete acoustic treatment plan that I need for my room", or "what's the next thing that will give me the biggest improvement of sound for my dollar for my room". In all cases the words "for my room" are important, and relative to what's going on in that room right now. Because for which is best for the room, that depends on what else is in there, and how sound is bouncing around.

Start a thread. State what's in the room right now (furniture, carpet, treatment), with drawings with measurements and photos. State what you perceive the acoustic problems to be (observations, anomolies, difficulties, examples, and/or measurements). State the budget, restrictions (like floorspace), and your "criteria for success". There are other acoustic issues than absorbtion, and moving speakers and furniture is a lot cheaper and easier.

Ready2Buy

02-03-06, 07:05 PM

Close.
Porous absorbers are velocity absorbers -- they absorb the most where the wave is moving the fastest. Spacing them off the wall does extend lower frequency absorbtion for the same cost in material.
For a sine wave the highest velocity is at the 1/4 and 3/4 wavelength points.
But
a) most sound doesn't go straight into a wall, so 1/4 wavelength out from the wall is just about meaningless. With 7 speakers, best case is 1/7th of the direct sound is hitting one spot on one wall straight into it. The rest is hitting at some angle. And after a few milliseconds all of the reverberant field can probably be considered fairly diffuse (all angles). Although the rear wall, relative to the front center speaker, might apply to this 1/4 wavelength (not a diffuse absorbtion test like those at http://www.bobgolds.com/AbsorptionCoefficients.htm), certainly all the sound hitting the first reflection point absorbers wouldn't be going straight-in-and-straight-out from the fronts because it's all hitting at an angle.
b) most sound isn't a sine wave, thus it probably doesn't have its maximum velocity at 1/4 wavelength
c) Just because the absorber is most efficient at the highest velocity part of the wave (1/4 wavelength for a sine wave), that doesn't mean it doesn't still work well at lower frequencies. As long as the air is moving it still works, just to a lesser degree. 701 plain 1" on wall has a 0.17 absorbtion coefficient at 125hz, even though 1" 1/4 wavelength would be 3390hz.
d) I think that most sound is travelling wave (as opposed to standing) may be relevent too.

Density is not a guarantee that it will work better at lower frequencies. There's not a lot of dependable lab work at under 100hz. One thing that higher density is known to do is reflect high angles of incidence for higher freqeuncy sound -- thus high density shouldn't be used for first reflection point absorbers, although you might try it on the rear wall.

Normal vs Grazing incidence (http://www.bobgolds.com/NormalVsGrazing.GIF)

Actually the best thing to do is to match the DVD recording engineer's RT60 spectrum, but that's impossible. Jeff of Auralex fame has done thousands of rooms, and he managed to get about two of them +-3db from 100hz to 8000hz. A little extra in the bass is apparently ok.

This is a pretty good comparison of absorbtion between
a) 4cm on the wall
b) 4cm, with a 4cm space behind it
c) 8cm on the wall
Theoretical Effect of Moving an absorber out from the wall (http://www.bobgolds.com/absorbtion%20Porous_Absorber_&amp_xls%204cm%20of%205.00%20kPasPERm2.GIF)

Note how absorbers flat parallel to the wall tend to absorb a lot of HF, but little LF, and it's pretty much a gentle slope between them with no peaks (other than the right hand side).
A lot of things you're likely to have in your HT, like carpet, have this absorbtion trend.

A corner absorber has an absorbtion curve like this
Studiotips Corner (http://www.bobgolds.com/StudioTipsCornerAbsorbtion.gif)
Note how its got a peak of absorbtion near 100hz, and the higher frequencies are relatively lower absorbtion.
This is one of the few (only?) porous things that have a different absorbtion trend.

Actually you want the room to be fairly dead. Not anechoic chamber dead, but certainly not 'live'.

Wow, what a great post!!! I think your point that a 1" panel still works at 125 Hz even though the popular "quarter wavelegth" theory states that maximum absorption happens for waves of frequency 3390 Hz and higher is an excellent point. Maybe a better theory is needed to understand this.

With regard to density, here is another observation. From your site I see the following absorption coefficients at 125 Hz:

701 plain 1" 0.17
703 plain 2" 0.17
705 plain 2" 0.16

Doubling up on both density and thickness did not change the absorption coefficient. Can we attribute this to bad measurements or is it real?

With respect to the measurements you posted on the wall with zero degrees incidence angle, the 4cm/4cm panel absorbs better than the 8cm/0cm panel even down low. Why? Meanwhile for diffuse sound field, the 8cm/0cm is best as would be expected. In any case, your graph clearly shows that the airgap does improve absorption under all circumstances. It also proves that panels on/parallel to the wall do not absorb low frequency sound very well.

Now WHY does the corner absorber show a large peak at 100 Hz? Does it have something to do with the air column between the absorber and the two corner walls?

The more you think you understand this stuff the more questions arise ...

John

Ready2Buy

02-03-06, 07:19 PM

The question is either "what's the complete acoustic treatment plan that I need for my room", or "what's the next thing that will give me the biggest improvement of sound for my dollar for my room". In all cases the words "for my room" are important, and relative to what's going on in that room right now. Because for which is best for the room, that depends on what else is in there, and how sound is bouncing around.

Hi Bob,

What happened to the popular:

"You can't have too many bass traps"

I thought this was true for any room that doesn't already have corner treatments. Is this NOT true?

John
PS: Thanks for all the help you provide in this forum and the outstanding website you keep.

BasementBob

02-03-06, 07:34 PM

Ready2Buy:

Doubling up on both density and thickness did not change the absorption coefficient. Can we attribute this to bad measurements or is it real? It's real.
125hz is well within the acceptable results testing range. (lower frequencies are not)
However, two things:
1) The same sample measured the same way in multiple labs has this uncertainty (http://www.bobgolds.com/AbsorbtionCoefficientsMultiLabs.jpg)
2) The effectiveness of absorbtion drops as you put more absorbtion into a room. These tests/results were done in a large reverb chamber, with an 8'x8' sample in the middle of the floor. If you do the same thing, you'll get the same results. If you put these things into your room, still flat on a surface and away from other surfaces (e.g. the middle of a wall), you'll get different values, but with a similar TREND.

It also proves that panels on/parallel to the wall do not absorb low frequency sound very wellI hope you mean 'shows', rather than 'proves'.
Mostly I just wanted to show more detail than the simple statement
4" on the wall IS LESS THAN 4" spaced 4" out from the wall IS LESS THAN 8" on the wall
Because the graph shows the relative difference as well.

Now WHY does the corner absorber show a large peak at 100 Hz? Nobody knows. There are no standards for corner trap measurments. Some experts have a half dozen educated guesses, all possibly true to greater or lesser degrees. One of my favourites is "edge effect without edges" -- think outside the corner trap too.

The corner trap measurements available to the public are
a) http://forum.studiotips.com/viewtopic.php?t=536
b) http://www.gikacoustics.com/absorption.htm
c) http://www.realtraps.com/data.htm
In all cases assume the tests are performed honestly, but don't take the values out of context. They are valid only for the way they were installed, and shouldn't be compaired. A little fiddling and I can make any of those products absorb more than the others at any frequency you'd care to name. Where the exact test is not described, it's like providing no information at all, other than perhaps the TREND. And the TREND is ultimately possibly all you could use anyway, because your room is not a reverb chamber. The studiotips example goes on and on about how the test is valid for comparison between the devices they tested, but can't be used outside of that narrow scope.

BasementBob

02-03-06, 07:51 PM

Ready2Buy:
"You can't have too many bass traps"
I thought this was true for any room that doesn't already have corner treatments. Is this NOT true?
I think Ethan Winer started that quote. And for the kinds of rooms that you and five of your friends are likely to walk into in your lifetime, and Ethan's experience installing his traps as corner traps into typical rooms, it's an honest observation.

But corner traps are not only bass traps, they affect higher frequencies too, so I'd have to disagree with your variation on his words. Also, corner traps are not the only bass traps -- I can't think of a DE Designed theatre that has a diagonal corner trap in it, but I can think of lots of membrane and helmholtz absorbers in those.

Worst stupid/insane case: if you 80% by volume filled a six-sided-concrete-room with 30hz tuned helmholtz port absorbers (bass traps), and no other treatment, not only would the sound be awful, but you couldn't see the movie because there's these big bass traps between the screen and the wooden dining room chair (as well as everywhere else). Adding another 30hz tuned helmholtz port absorber to the room because "You can't have too many bass traps" wouldn't help.

(BTW, I use the words "DE Designed" to mean something that Dennis was paid to do, as opposed to "DE Style" which is "cover the front wall in absorbtion, and the side and rear walls 50% of the way up". DE Designed is better than DE Style, every time.)

I should mention again, that I give ideas, not advice. I am, by far I suspect, the most overthinking amature on this forum. I've been thinking about HT for three years, and what I've got is this: http://www.bobgolds.com/HomeOffice/home.htm Most (all?) people shouldn't delay and waste as much time as I have. I want to do it once, and getting that last 5% of performance is taking me a rediculous amount of time.

stromand

02-04-06, 01:31 AM

I should mention again, that I give ideas, not advice. I am, by far I suspect, the most overthinking amature on this forum. I've been thinking about HT for three years, and what I've got is this: http://www.bobgolds.com/HomeOffice/home.htm Most (all?) people shouldn't delay and waste as much time as I have. I want to do it once, and getting that last 5% of performance is taking me a rediculous amount of time.

BasementBob,

I almost fell off my chair LOL after I read this quote and viewed your pictures. I think your pictures should be titled "What happens when you buy the projector before finishing the construction"

Thanks, sometimes these threads get a little to serious.

Stima

02-04-06, 02:19 AM

(BTW, I use the words "DE Designed" to mean something that Dennis was paid to do, as opposed to "DE Style" which is "cover the front wall in absorbtion, and the side and rear walls 50% of the way up". DE Designed is better than DE Style, every time.)

Glad you cleared that up. I was a little cunfuzz'd about "DE style", ect. ;)

Ethan Winer

02-04-06, 11:55 AM

John,

> "You can't have too many bass traps" I thought this was true for any room that doesn't already have corner treatments. Is this NOT true? <

It is absolutely true. Even with a ton of bass traps you'll still have some skewing of the response and some ringing. So the real question is how much are you willing to tolerate? However, this is true only for bass traps, and probably not for mid and higher frequencies.

I also agree with Bob's point about corner testing. The ASTM C-423 standard explains that labs can vary as much as 50 percent at 125 Hz. I have found they can vary by 300 percent at 100 Hz and below. But as Bob said you can see trends when testing the same material in the same places in the same lab. As soon as you move the materials even a few inches the measurements can change substantially. And do the same test in a different lab and any comparison is impossible.

--Ethan

Ready2Buy

02-04-06, 01:42 PM

Ready2Buy:

The same sample measured the same way in multiple labs has this uncertainty (http://www.bobgolds.com/AbsorbtionCoefficientsMultiLabs.jpg)

One of my favourites is "edge effect without edges" -- think outside the corner trap too.

And the TREND is ultimately possibly all you could use anyway, because your room is not a reverb chamber. The studiotips example goes on and on about how the test is valid for comparison between the devices they tested, but can't be used outside of that narrow scope.

BasementBob:

Good stuff, brings up even more questions.

(1) From the uncertainty graph you posted I see that measuring absorption below 100 Hz produces errors as large as 50%! If this is the case then all absorption numbers posted by the various bass trap vendors, including the three links you posted, could be half of their posted values! This means that one could seriously under-estimate the amount of low frequency trapping he needs by as much as a factor of 2.

(2) What do you mean by "edge effect without edges"? Is this another concept/design for bass traps? Excuse my ignorance I just started learning this stuff but, like you, I want to do this once and do it right.

(3) I think it's clear from the studiotips example that if you want any bass traping below 100 Hz you have got the fill up the corners of your room. In that comparison graph it looks like the superchunks with the 34" face does a great job below 100 Hz even though its TREND is dropping fast below the 100 Hz peak. It looks like it will still absorb good at 56 Hz where I got a couple of big room modes. (My room is square 20'x20'x8' with carpet and two leather couches in it).

(4) In one of the studiotips corner trap designs the following statement appears:
"Owens Corning 703 is a material which has been used with success, but lower density products of this class may be cheaper and actually work slightly better low in the band." LOWER DENSITY products work better at lower frequencies??? This is contrary to other statements made here and elsewhere that OC-705 is better at lower frequencies because its denser and therefore more difficult for the longer waves to pass through it. Yet another of the conflicting pieces of loose information out there.

(5) The studiotips excel file:
http://forum.studiotips.com/download.php?id=970
shows the two fiberglass-based corner trap designs. The classic "studiotips corner absorber" was a 2'x8'x4" tower straddling the corner. It was made by stacking TWO 2'x4'x4" OC703 panels. However, the 34"-face "Superchunks" was made using SIX 2'x4'x4" panels. That's three times more fiberglass than the classic design which resulted in only 50% more absorption at 63 Hz. First it is clear to me that this is an unfair comparison. A more fair comparison would be to modify the classic design so that it uses six panels instead of two. The easiest way to have done this is to create a 2'x8'x12" tower using six 4"-thick panels and straddle the corner. I bet the classic design would be better than SuperChunks if it was made three times thicker. The problem with this comparison would be that the 6-panel classic "system" would now have an airgap behind it while the superchunks doesn't. So a fair comparison might have been the 6-panel superchunks against a 4 panel classic (2'x8'x8").

(6) My own thinking led me to a design that was a 2'x8'x24" square tower shoved in the corner. But I only have 63 2"-thick panels and I would 96 to implement this at 4 corners. I am now rethinking that I could go with 2'x8'x10" towers stradlling the corners. I am still thinking about this and other options too.

Best,

John

Terry Montlick

02-04-06, 02:05 PM

(4) In one of the studiotips corner trap designs the following statement appears:
"Owens Corning 703 is a material which has been used with success, but lower density products of this class may be cheaper and actually work slightly better low in the band." LOWER DENSITY products work better at lower frequencies??? This is contrary to other statements made here and elsewhere that OC-705 is better at lower frequencies because its denser and therefore more difficult for the longer waves to pass through it. Yet another of the conflicting pieces of loose information out there.

Not conflicting, John. Just more complicated than a simple rule.

There is a tradeoff between density and thickness. Too dense an absorber, though theoretically thick enough to absorb very low frequencies, won't allow sound waves to penetrate sufficiently to its entire depth. So for an absorber of large depth, a less dense material works better beyond a certain point.

An alternative is to add an airspace behind dense material. This lowers the total amount of absorber thickness the waves have to travel through, while still affecting low frequencies comparably. This airspace approach doesn't come for free. You get "ripple" in the frequency response, rather than smooth absorption.

Make sense?

Regards,
Terry

Ready2Buy

02-04-06, 02:22 PM

But corner traps are not only bass traps, they affect higher frequencies too

I thought one way to deal with this is to use a less breathable fabric that reflects high frequencies. I still don't know what exact fabric to use though.

but I can think of lots of membrane and helmholtz absorbers in those.

I am afraid I can't build those but I sure can throw fiberglass in the corners in vast quantities

I've been thinking about HT for three years, and what I've got is this: http://www.bobgolds.com/HomeOffice/home.htm Most (all?) people shouldn't delay and waste as much time as I have. I want to do it once, and getting that last 5% of performance is taking me a rediculous amount of time.

Nice office/HT combo. But where are the bass traps? I can't see them in the pictures. Are they cleverly hidden from view?

John

Ready2Buy

02-04-06, 02:39 PM

John,
I have found they can vary by 300 percent at 100 Hz and below. But as Bob said you can see trends when testing the same material in the same places in the same lab.
--Ethan

Thank you Ethan. But if they vary by 300% below 100 Hz, then there is no way of estimating anything. And what am I suppose to make of the "trend" other than it goes down at low frequencies? In fact that's exactly where I need the traps to work!!!

The important thing I am getting is that the more fiberglass you use the better off you are provided that you do something to avoid over-absorbing the high frequencies.

John

Ready2Buy

02-04-06, 02:45 PM

Not conflicting, John. Just more complicated than a simple rule.

There is a tradeoff between density and thickness. Too dense an absorber, though theoretically thick enough to absorb very low frequencies, won't allow sound waves to penetrate sufficiently to its entire depth. So for an absorber of large depth, a less dense material works better beyond a certain point.

An alternative is to add an airspace behind dense material. This lowers the total amount of absorber thickness the waves have to travel through, while still affecting low frequencies comparably. This airspace approach doesn't come for free. You get "ripple" in the frequency response, rather than smooth absorption.

Make sense?

Regards,
Terry

Very nice explanation Terry. But how are we supposed to know where the threshold is? And why aren't more people using 705 for corner traps? Seems like 703 or 703-equivalent (i.e., the 3-pound densities) is the flavor of choice from what I see on the net.

Best,

John

Terry Montlick

02-04-06, 03:08 PM

Very nice explanation Terry. But how are we supposed to know where the threshold is? And why aren't more people using 705 for corner traps? Seems like 703 or 703-equivalent (i.e., the 3-pound densities) is the flavor of choice from what I see on the net.

Best,

John
Hi John,

Finding the threshold is part of my business. I design bass traps, other acoustical treatments, and entire rooms for money :). I've spent years studying the theory and practice of sound absorption. You can slog through the equations in the professional literature yourself for a few years, or hire me (low hundred of bucks) to design the bass trap of your dreams :D.

I can't reveal my proprietary tricks for free. But I try to give away as much info as practical, and steer people in the right direction.

Regards,
Terry

Joel DuBay

02-04-06, 04:01 PM

One of the reasons people steer clear of using OC705 is cost, and if you look at published acoustical data for FRK and FSK 705, you'll see spikes at 100hz. This is not true of all commercially made acoustic panels that use 705, but it is true or many. There is some test data available through Belgian laboratories and US reverb chambers that should some of the best overall results come from using OC 703 (unfaced) as a broadband absorber. The advantages to the DIY guy are that it is easier to work with, offers a wider broadband absorption coefficient, and costs less than half the price of OC705...and..... it is typically more readily available to the DIY'ers.

We'll be publishing a DIY solution at the website that will show you just how to make your own, with little fuss and a high WAF. (wife approval factor).

Stay tuned, and good luck.

Terry Montlick

02-04-06, 07:44 PM

...
At low frequencies, the change in the Diffraction Effect is much more powerful (in sabins) than the increase in surface area -- and since we're ga ga about bass absorbtion, this is worth paying attention to.

When a porous material is separated, such as in a checkerboard pattern, its absorbtion changes.
Usually more absorbtion in the bass, with little change in the trebble
"The discontinuity in the wave field at the edge of the specimen create a diffraction effect that warps the sound field to make the specimen appear as much as a quarter-wavelength larger in each direction." (from Proceedings of Noise Con 90, David A. Nelson, P.E., INCE Bd. Cert., "Diffraction Effect" in Sound Absorption Tests: Why is the sound absorption coefficient greater than 1.00?)

The first paper I have describing this phenomenon is from 1930. !!!

- Terry

Ready2Buy

02-05-06, 12:03 AM

There is some test data available through Belgian laboratories and US reverb chambers that should some of the best overall results come from using OC 703 (unfaced) as a broadband absorber. The advantages to the DIY guy are that it is easier to work with, offers a wider broadband absorption coefficient, and costs less than half the price of OC705...and..... it is typically more readily available to the DIY'ers.

Hi Joel, thanks for confirming this. Most of the reputable reports on fiberglass absorbers appear to favor the 3-pound densities.

We'll be publishing a DIY solution at the website that will show you just how to make your own, with little fuss and a high WAF. (wife approval factor)

Looking forward to your DIY article. Will you be posting it any time soon?

John
PS: The "bag" product idea is quite interesting as it allows for local purchase of the fiberglass which practically eliminates the hefty shipping costs of finished panels. You may want to consider making it available for thicker panels (i.e., 6" and 8" thickness).

Ready2Buy

02-05-06, 12:18 AM

Hi John,
You can slog through the equations in the professional literature yourself for a few years, or hire me (low hundred of bucks) to design the bass trap of your dreams :D.

I can't reveal my proprietary tricks for free.
Regards,
Terry

I read you loud and clear Terry ;) I just happen to be one of those guys who must understand the basics prior to attempting to do anything. The goal is to try to acquire enough basic knowledge about a topic so as to not screw my own self (pardon my language) in the implementation phase :D

Best,

John

Ready2Buy

02-05-06, 10:39 AM

The first paper I have describing this phenomenon is from 1930. !!!

- Terry

Hey guys, did we lose a post from BasementBob? (the one Terry is replying to on "diffraction effects")

Ethan Winer

02-05-06, 11:51 AM

John,

> if they vary by 300% below 100 Hz, then there is no way of estimating anything. <

Sad but true.

> And what am I suppose to make of the "trend" other than it goes down at low frequencies? In fact that's exactly where I need the traps to work!!! <

If you buy commercial panels from a company with a good track record, or follow the various DIY threads and plans based on rigid fiberglass straddling corners, I promise you'll get good bass trapping. For sure some bass traps are better than others, but even a mediocre bass trap is far better than nothing.

> The important thing I am getting is that the more fiberglass you use the better off you are provided that you do something to avoid over-absorbing the high frequencies. <

Yes, exactly.

> But how are we supposed to know where the threshold is? And why aren't more people using 705 for corner traps? Seems like 703 or 703-equivalent (i.e., the 3-pound densities) is the flavor of choice from what I see on the net. <

See my Density Report:

www.ethanwiner.com/density/density.html

It's all in there.

--Ethan

tonybradley

02-05-06, 02:21 PM

I've been following this thread and will be purchasing my 2" 703 boards in a week or two. I have a VERY general question. I know my room needs treatments as it's a total reflective room now (drywall all around, drywall tiles for drop ceiling, and thin carpet). Currently, any movie with High Pitched sounds (i.e. Menu screen of Jurassic Park III when the claw marks enter the screen) is extremely painful to the ears. Same with the Glass shattering when the machine first enters on War of the Worlds.

Will the panels at first reflections help tame those highs to where they won't be so painful?

I can't localize my surrounds at all. Honestly, you can't even really tell they are there until it's one of the only speakers working. Again, I think this is because it's being covered up so much with all the reflections going on in my room. The volume levels are calibrated. Will the panels help this problem as well?

I've been experimenting with sub placement. Today I found the best place for my room (between the center speaker and the right main). Thing I'm discovering (volume level is calibrated to the same level as other speakers) is that the sub isn't too loud on SOME scenes where it should be. Would the High frequencies that are reflecting all around the room also hinder what I hear from the Sub..maybe drowning it out some? I will be adding bass traps as well, but just wondering if adding the 2" 2x4 panels on the side and front walls will at least help the sub a little. I've ran some frequency sweeps and there are peaks and dips through the frequency range (of course..no treatments).

Tweakophyte

02-06-06, 09:31 AM

See my Density Report:

www.ethanwiner.com/density/density.html

Jeez... how could I have missed that one? I skimmed it an am going to read it later...

...hope it's a slow day at work today :D

bpape

02-06-06, 10:43 AM

tonybradley

02-06-06, 12:19 PM

Tony,

On the bass, it's more likely that the ringing and excessive decay times on the bottom end are in effect covering themselves up. When you get the decay under control, you'll find it smoother and more articulate. It will also likely appear louder and deeper in the bottom end.

As for the highs, it's hard to say. Controlling the reflecions will help to make things more dynamic and 'image' better. Some overlap due to excessive decay times can cause some harshness. What speakers are you using?

I have some older Infinity speakers. RS-5 for the mains and the CC-3 center speaker. My receiver is a Denon 2805. Anything that's high pitched is very painful. I don't even listen at Reference Level (slightly lower). That's why I was curious (in a totally reflective room - carpet on floor and chairs) if reflections could magnify these harsh high frequencies and the treatments would tone them down. For example, a few of my friends watched a couple of scenese from War of the Worlds at my house. When the glass shattered in the buildings, it was screatching loud. My ears were actually hurting. We took it to my friends house who has floor to ceiling carpet (yes I know, bad idea). His sounded so much better, but maybe a little too dead as the glass shatter didn't appear dynamic enough. Are you thinking this could be more my speakers and not so much reflections in the room?

Ready2Buy

02-06-06, 02:28 PM

John,

See my Density Report:

www.ethanwiner.com/density/density.html

It's all in there.

--Ethan

Hi Ethan,

First let me congratulate you on your report. Nice work and an excellent attempt to fill in the knowledge gap in the density/thickness area. The only problem I have with your work is that the differences you observed at low frequencies between the various densities/thicknesses and mountings appear to be rather miniscule to justfy any really strong conclusions. In fact I am wondering if you are not reporting measurements that are "below the noise level". If you were to repeat this test how sure would you be that you would get the same small differences in these results?

From your density report:

"So what can we learn from these graphs? First, it's evident that for all of the fiberglass types it's better to have twelve thinner panels spread more completely around the room than only six thicker panels covering less total surface area."

I definitely agree with this. It says that for thick panels, more absorption occurs in the first half of material thickness than the last half of material thickness. So spreading thinner material all around produces the conclusion you reached. Spreading does produce more bass absorption but at what cost? Certainly at the cost of consuming more surface area. But the bigger cost maybe that it results in over-absorption of the mid- and high frequencies, a problem we don't want.

Another piece from your report:

"For the density comparisons with 12 panels, in each case increasing the density reduced the ringing time and lowered each mode's Q more than the less dense versions."

This is not a quantitative result. How much did it lower it and what are the statistics of the error in your measurements? Also, how much damage did it do to the high frequency range? These are good questions that would need to be addressed in a test like this.

Another:

"This also shows that density appears to become less important when the panels are made thicker."

I like this one, and I believe it. Good result.

Another:

"However, even with only six 6-inch panels 705-FRK still emerges the clear winner, if only by a small amount at 42 Hz."

Now this one I am not so convinced. "Clear winner" but by a nano-Sabin! The magnitude of the difference could easily be attributed to measurement noise.

John

Ready2Buy

02-06-06, 02:44 PM

Will the panels at first reflections help tame those highs to where they won't be so painful?

Hi Tony,

If you already have a finished room and you spend enough time reading these threads you will notice the following trends emerge:

(1) Buy fiberglass (OC-703 or equivalent) and frame/wrap in fabric
(2) Straddle as much as you can in all corners of you room for bass
(3) Place "thinner" panels on walls/ceiling at all first reflection points
(4) If you have material left-over, consider putting in on the front wall
(5) Make the back wall diffusive (i.e., bookcases will work)

The challenge is to pull this off with style and make everything look good in the room (high WAF). The challenge presented in this last point should not be under-estimated.

Best,

John

bpape

02-06-06, 02:50 PM

Ethan Winer

02-06-06, 05:00 PM

John,

> I am wondering if you are not reporting measurements that are "below the noise level". <

I agree the changes at the lowest frequencies are minor, but they are larger at higher frequencies and the trend is pretty clear. This is why I tested three densities instead of only two. As soon as R+D gets a little closer to "ready for prime time" I plan to go back and analyze many of my previous ETF tests in more detail. One big failing of ETF is its LF tests go only to 200, and I believe seeing the response up to 300 Hz gives a much better overall impression.

> This is not a quantitative result. How much did it lower it and what are the statistics of the error in your measurements? <

Hey, it's a first attempt done entirely as a labor of love. If you'd like to fund continuing research into this I'll gladly tell you where to send the cash. :D

> how much damage did it do to the high frequency range? <

Damage? This was a test of how density affects low frequency performance.

> "Clear winner" but by a nano-Sabin! <

I might agree except the change was larger at higher bass frequencies. Look at the peak just above the 92 Hz marker. Again, this was for only six panels. The differences are much larger for 12 panels.

--Ethan

Ready2Buy

02-06-06, 05:13 PM

John,
> how much damage did it do to the high frequency range? <

Damage? This was a test of how density affects low frequency performance.

--Ethan

Ethan,

By "damage" I meant over-absorption. You can't just try to optimize for absorption at low frequencies without regard to the absorption at higher ones. I thought we agreed on this. You may in-fact be getting a little better absorption with the panels over a larger surface area but it's not clear what is the price paid for this. I am merely suggesting that the cost of spreading the panels to cover a wider surface area maybe over-absorption at high frequencies.

John

tonybradley

02-06-06, 08:08 PM

Tony.

In a former life long ago and far away, I used to sell the Infinity's you have. Yes. They can be a bit forward. IMO, it's not so much the highs as it is the upper mids and the xover execution in those speakers. I do think that taming the reflections and the overall decay time will help. Those tweeters are pretty beamy so getting them under control should be relatively easy in comparison to some other drivers.

When you went to the other house, did you take your speakers? Just trying to compare apples and apples.

I guess I need new speakers (refering to them in your past life is a bad sign) ;)

Unfortunately, I did not take my speakers to his place, which is my next project. I've had these speakers for about 6 or 7 years. I've never noticed them this screatching until this room with the Denon receiver.

Hi Tony,

If you already have a finished room and you spend enough time reading these threads you will notice the following trends emerge:

(1) Buy fiberglass (OC-703 or equivalent) and frame/wrap in fabric
(2) Straddle as much as you can in all corners of you room for bass
(3) Place "thinner" panels on walls/ceiling at all first reflection points
(4) If you have material left-over, consider putting in on the front wall
(5) Make the back wall diffusive (i.e., bookcases will work)

The challenge is to pull this off with style and make everything look good in the room (high WAF). The challenge presented in this last point should not be under-estimated.

Best,

John

My wife is cool with whatever I do to the dedicated room. I already have my plan on how I"m going to do the treatments. Now to just find the time with two little ones running around.

Ciscokid

02-06-06, 10:35 PM

Hi all, I am just beginning to change my family room into a theatre area. I know its not the perfect spot for it since my home is a totally open floor plan. I need to pick your brains on some ideas to help my room out (acoustically). The biggest thing bothering me is echo. Here are the dimensions of my room. 13.5 wide by 21 feet long with 8 foot ceilings. This is just my Family room,its another 22 feet to the back of the kitchen. The room is rectangle in shape with 2 windows and a fireplace between them on one side. The other wall is solid all the way to 18 feet where there is a hall area that branches off to my bathroom and laundry room.I am setting up a projector in the room. Do I need to worry about the front wall behind the screen? Should i put some absorbtion on this wall? I was thinking of putting a bass trap in both front wall corners. Also putting absorbtion on first reflection points on sidewalls and ceiling, if the wife will let me. She is not to fond of the looks of the panels I have been showing her. :)
Another concern is not having a back wall. Since my room is open to the kitchen is there anything I can do that will help? I have a soffit at 21 feet that kind of divides the family room and kitchen. My wife had an idea of building a coffer ceiling in the family room. Which I kind of shot down cause I thought it would make the room even worse than it already is.Well Thanks for any information you can provide me.

bpape

02-07-06, 07:31 AM

Cisco.

If that's the room you have to work with then you'll just have to work with it.

If you can do the front 2 corners and the side refleciton points, that will help a lot. As for the back being open, well, not much you can do there. Deaden the front wall. That will help overall and also will help minimize issues from the rear. Honestly, that dimension is likely not your biggest issue since it's SO long.

Sounds to me that you have some serious issues in the room middle with glass and brick on one side and drywall on the other. I'd shoot for nice heavy curtains over the windows and panels on the side wall opposite it.

Tony,

If you've not had this problem before, then it's either the room or the receiver/speaker interaction, or both. I'd try to eliminate things one at a time - though IMO going to a room with carpet all over the walls is not a good comparison - sorry.

I'd first try borrowing a different receiver (though the Denon is generally considered anything but harsh - if anything too laid back). Then go back to the Denon and even just go get some decent smaller rugs from HD and tack them to the walls where your reflections are just as an experiment.

Tweakophyte

02-07-06, 09:07 AM

Ethan-

Nice write-up. I am still trying to decide what the best way to use 3 pieces of 2" thick rigid fiberglass (each 4' tall due to constraints) for low-to-broadband bass trapping. The original options were to make a 6" thick corner trap, a 24" face cornerchunk, or a 4" thick coner trap with another peice wedged in the corner itself.

Based on it you can almost infer it to be best to make a 4" thick panel ("corner absorber") and use the other peice to cover more area. This is because it looks like there's diminishing returns on pure thickness. Now I am thinking of using the additional piece to maker a wedge for the top of the panel, which would add more surface area.

Also, I wonder if part of what you measured is due to the water splashing effect Bob mentioned, and the top-to-bottom configuration handling that better than the half-wall. (make sense?) Next time (if we're lucky enough) maybe you could double up on the vertical corners and create several thicker top-to-bottom panels instead of half-height panels.

Thoughts?

Ethan Winer

02-07-06, 03:54 PM

John,

> By "damage" I meant over-absorption. You can't just try to optimize for absorption at low frequencies without regard to the absorption at higher ones. <

You continue to miss that this was pure research into the relationship between density and low frequency performance. It is not an article explaining how best to treat a room.

--Ethan

Ethan Winer

02-07-06, 03:58 PM

Ciscokid

02-07-06, 07:30 PM

Bpape,

Thanks for the information. Now your saying to deaden the wall behind the screen right? Do I need to cover the entire wall top to bottom, or just put some absorbtion panels centered on the front wall behind the screen. Along with the two bass traps in the corners. Should I also do the ceiling if possible at the first reflection point? Thanks again for the information.

Ready2Buy

02-07-06, 10:46 PM

John,
You continue to miss that this was pure research into the relationship between density and low frequency performance. It is not an article explaining how best to treat a room.

--Ethan

Ethan,

I got you. As you can see my interest is in the big picture, i.e., how to best treat a room. The entire room and over the entire frequency range, 20Hz-20KHz.

Best,

John

Tweakophyte

02-08-06, 08:32 AM

Tweaks,

> I am still trying to decide what the best way to use 3 pieces of 2" thick rigid fiberglass (each 4' tall due to constraints) for low-to-broadband bass trapping. <

I'd say you can't, because that's simply not enough material to do the job. The absolute minimum to make a real improvement in a "normal" size room is two panels - one in each front corner - 2 by 4 feet at least 3 inches thick. Though a "better" minimum is four panels in all four corners.

> I wonder if part of what you measured is due to the water splashing effect Bob mentioned <

I'm not sure which post you mean, but all of the panels in my test were in exactly the same place. So I'd say the exact mechanism for the change with density doesn't matter so much.

--Ethan

Hi Ethan-

I should clarify that I am planning on some front wall and first reflection treatments in my room. I am also going to make bass traps for at least the rear corners of the room, and eventually the front corners. I might also do a floor/wall corner.

My issue I can only do a half-height trap in any given corner because of sconces and vents. I did play around with a bag containg 5 panels being placed in one corner and the effect was very noticable when I played a techno song that had several long reverse bass sweeps in it. Maybe I'll play around with those panels a bit more before I make frames.

---
Btw, Bob's swimming pool analogy is here:
http://www.avsforum.com/avs-vb/showthread.php?p=7045983&&#post7045983
and it is in regards to the notion that sound hitting a wall having zero velocity. Think of a swiming pool. Make a splash (wave) on the surface, and the wave goes towards the wall, goes up the wall (stops velocity at the wall as the wall changes the wave from horizontal velocity to vertical potential energy), reflects, and returns.

My thought is with half-height panels that don't have the benefit of two tri-corners you could cap-off the open end of a simple corner panel and trap some portion of the splash. If anything it would add a small amount of surface area to the bass trap. Make sense?

rsante

02-08-06, 09:41 AM

Terry Montlick

02-08-06, 09:46 AM

Roger,

Try any of the books by F. Alton Everest, such as "Master Handbook of Acoustics." These are highly readable and provide a good layperson's intro to the basics.

- Terry

bpape

02-08-06, 11:43 AM

Cisco.

I do recommend doing the entire front wall. There is some disagreement on this but IMO it's important to do it in a multichannel environment. This is done in addition to the bass absorbtion.

Ready2Buy

02-08-06, 03:20 PM

Roger,

Try any of the books by F. Alton Everest, such as "Master Handbook of Acoustics." These are highly readable and provide a good layperson's intro to the basics.

- Terry

I just got this book last night. From the little that I have read so far I would recommend it highly. Very easy to read if you have a little bit of technical background.

Ethan Winer

02-08-06, 03:44 PM

John,

> my interest is in the big picture, i.e., how to best treat a room. <

There's a huge amount of info about that on my personal and company web sites.

--Ethan

Ethan Winer

02-08-06, 03:46 PM

Roger,

> Is there a place (or book, or video) that I can get that will show me the basics of acoustics to that I can understand the posters in this forum better? <

You bet, see my Acoustics FAQ:

www.ethanwiner.com/acoustics.html

It's all in there.

--Ethan

Ethan Winer

02-08-06, 03:48 PM

Tweaks,

> My thought is with half-height panels that don't have the benefit of two tri-corners you could cap-off the open end of a simple corner panel and trap some portion of the splash. If anything it would add a small amount of surface area to the bass trap. <

With bass trapping, what matters most is havng suitable material, its thickness, and the total surface coverage. And correct placement, of course. This is not to say that all corner locations are equal. Some places might help one frequency more than another.

--Ethan

Joel DuBay

02-08-06, 05:53 PM

I read these posts....then reread these posts and I still come away scratching my head. Highs..mids...lows....density vs. thickness...it's almost enough to make my mind turn to jelly.

Is there a place (or book, or video) that I can get that will show me the basics of acoustics to that I can understand the posters in this forum better? Say, an "Acoustics for Dummies" kinda thing?

Roger, I understand that acoustics information here and elsewhere can be confusing. There are many books available and many additional resources on the net that make the complicated matter of acoustics, much easier to digest. One way to understand acoustical "treatment" is to visualize it. You might be able to grab more of the info available via its practical application. For instance, you can see an acoustically treated room in this diagram. Typical Home Theater with Acoustic Treatment (http://www.readytraps.com/Ready_traps/Home Theater Room/pictures/Theater_Room_large view_Rside.jpg) And, you can view a 3D image tour of an acoustically treated home theater here: Tour an Acoustically Treated Home Theater (http://www.readytraps.com/Ready_traps/Home Theater Room/movie/Home Theater Room.mov) This Quiktime movie is about 6MB, but gives you a good idea of how a room is typically treated. Hopefully, images with help information make sense.

I hope this helps.

Cheers,

Ready2Buy

02-08-06, 07:21 PM

Tour an Acoustically Treated Home Theater (http://www.readytraps.com/Ready_traps/Home Theater Room/movie/Home Theater Room.mov) This Quiktime movie is about 6MB, but gives you a good idea of how a room is typically treated. Hopefully, images with help information make sense.

www.readyacoustics.com (http://www.readyacoustics.com)

Joel,

Thanks for posting the animation, very easy to understand. Two questions for you regarding the treated room pictures:

(1) The bass traps at the 4 corners from floor to ceiling are only 4" thick. Jon Risch recommends at least 8" thickness to get down lower in frequency. Do you agree or disagree?

(2) Are the 4 panels behind the couch necessary? (They are not at first reflection points)

John

edfowler

02-08-06, 09:47 PM

Stima

02-09-06, 12:35 AM

Ethan,

I have read through many pages on your site. It appears you have done a ton of empherical study from which I am going to base my acoustical treatments.

To that end, can you please advise if I have missed anything:

Bass traps: I don't have space to put bass traps along the walls, but will utilize the corner trapping method. I plan to straddle the rear corners with 24" wide by 4" deep foil backed OC705 covered in any "breathable cloth" with the foil facing the room. Also, I am going to make several columns of stacked and coiled R12 insulation behind my screen wall. (I have a "bay window" area behind the screen, thus no 90deg corners to "straddle").

Mid\High Wall treatments: 2" OC703 covered in any "breathable" cloth. Floor to ceiling treatment of the "three sides" of my front wall behind the screen, and both side walls just past first reflection. Don't want foil covered OC703 as it refelcts hi's. I also plan to treat the bottom half of the rest of the side walls with OC703 and the entire (floor to ceiling) back wall. The top half will use 1" batting covered by an acoustically transparent cloth (GOM 701). I don't plan to put anything on my ceiling and have thick burber carpet on the floor.

As a sidebar: your article didn't go into sound decoupling between rooms, but I was wondering how a prodcut such as Dynamat would work behind the acoustical treatments? This product would GREATLY increase the weight of the walls. There is a foil covered version that could be used on the upper half of the walls to preserve "reflectiveness". Any thoughts?

Thanks a bunch,
Stima

bpape

02-09-06, 12:10 PM

John.

The panels in the rear of the room and on the rear sides are more for overall decay time control rather than early reflections. It is important to have absorbtion throughout the space for efficient control.

As for the bass absorbers, various things will work. 4" of a denser material straddling a corner with some space to the boundary will work well. If you're going to use a less dense material then more thickness added to the mix will certainly help.

Joel DuBay

02-09-06, 12:30 PM

I've waded thru hours of reading and may have missed it. I know it has been asked but I didn't see an answer.

I plan on putting 1" Certainteed duct board on the entire front wall. BUT...

do I drywall it first or leave the studs and the 6" of fiberglass insulation directly behind the duct board?

thanks

ed

Ed,

There are a number of ways to do this. For better bass response, insulating behind you drywall will work well. However, this will do little to help your first reflections. If I am seeing your wall and room layout in my head correctly, using rigid insulation behind the drywall might offer a better aesthetic, but you will probably want to do 'some" first reflection treatment as well there. But, not so much that you lose all of your highs.

Ethan Winer

02-09-06, 02:48 PM

Stima,

> please advise if I have missed anything: <

That all looks good.

> your article didn't go into sound decoupling between rooms <

Right, because I don't consider myself expert enough with that aspect of acoustics. I can tell you that most of the products I've seen (other than Green Glue) are not as good or as inexpensive as simply adding another layer or two of sheet rock.

--Ethan

Ready2Buy

02-10-06, 02:24 AM

Any comments on the following materials for wrapping fiberglass :

(1) First polyester batting:

http://storesonline.com/site/490194/product/MM-CG-2028-CASE

(2) Then grille cloth:

http://www.partsexpress.com/pe/pshowdetl.cfm?&DID=7&Partnumber=260-335&raid=44&rak=260-335

I am a little unsure about the polyester batting. There are so many different types, weights, lofts, etc that it is not clear which one works best with the fiberglass trap. (For example I have seen conflicting information on the internet boards regarding whether it should be low loft or high loft.) Please help on this one.

I am now converging on the following process for bass traps:

-First tape together several 2"-thick fibeglass boards
-Then wrap the assembly in polyester batting
-Then insert into wood frame
-Then wrap frame with grille cloth and staple to wood in back
-Then vacuum the surfaces of the fabric
-Then bring inside the house and place straddling the corner
-Done. Now go build the "thin ones" for first reflections.

John

jimsiff

02-10-06, 03:13 AM

I've read through the thread, and I've put together a rough draft treatment plan.

My HT is a multi-purpose family room with bar. It's roughly 14'10" x 18'6" with 8' ceilings. The floor is berber carpet and pad over a concrete slab. The two outside facing walls are 1' concrete covered in drywall up to 4', with standard 2x6 stud and drywall from 4' to the ceiling. The other walls are stud and drywall. WAF dictates general theater layout and furniture positions, so I have put together my plan based on those requirements.

I have included a few pictures of the room as well as a drawing showing my treatment plan.

http://www.sifferle.net/theater/theater.jpg
http://www.sifferle.net/theater/Theater%20001-web.jpg
http://www.sifferle.net/theater/Theater%20002-web.jpg
http://www.sifferle.net/theater/Theater%20003-web.jpg
http://www.sifferle.net/theater/Theater%20004-web.jpg

I would appreciate feedback on my general layout and treatment plans. I plan to first find the best spot for my sub within my available areas, then treat the room, then use my BFD to fine tune the bass FR.

I have some questions as well:

1) For my corner traps, I'm contemplating either an 8' 4" thick panel across the corner, or a "super chunks" style trap. Would I gain a lot of absorption by going with the "super chunks" style trap? It would use roughly 50% more material.

2) What material (acoustical cotton, mineral wool, fiberglass) would be most suitable for a kid friendly environment? I've got a toddler and 6 and 7 year old. I plan on covering whatever I use with grill cloth or muslin.

3) Where can I find absorption coefficients for 8# minneral wool vs. 4" acoustical cotton vs. 4" OC703/705? Is there a significant difference between the three?

4) If you look at my pictures and drawing, the first reflection points for my L/C/R speakers is mostly covered by the back of the couch and loveseat. There is about 1' between the top of the couch and the shelf at 4'. Would I be okay just putting the absorption panel on the shelf, or should I make a 1' tall absorber to treat that small area as well?

Thanks a bunch!

Terry Montlick

02-10-06, 08:19 AM

John -
The grill cloth is just fine, but the polyester batting is an unknown quantity. There is no density information given, and without that I don't know the absorption. Generally, when you pack light polyester batting to make it denser, it will "pillow out," and create an unsightly bulge.

Jim -
Acoustic cotton has about the same flow resistance as fiberglass of the comparable density, which is to say it has comparable absorption. Mineral wool has significantly more flow resistance for the same density as the other two, which means it has somewhat different absorption. I don't have measured coefficients for mineral wool this thick (don't think it is sold in 100mm thickness), but it should reach slightly lower in the lowest bass (maybe <50 Hz), quite possibly at the expense of higher bass frequencies.

Regards,
Terry

Terry Montlick

02-10-06, 08:37 AM

Meddy

02-10-06, 03:10 PM

I am getting close to the insulation phase of my basement theatre and was at HD the other night looking at the different insulation products. I have read about the Roxul Safe'n'Sound as being a good product to use but noticed in the bin next to it the Flexibat. Safe'n'Sound is about $5 a bag more expensive (both cover the same area)/ However the Safe'n'Sound is only a 3" thick batt while the Flexibat is 3.5" thick.

The Roxul website says the Safe'nSound has a density of 2.5lbs/ft3 while Flexibat is only 2lbs/ft3. Am I paying the $5 a package extra for the fire retardant in the Safe'n'Sound or is the 1/2 lb of density worth the extra price paid. Thanks in advance!

Ready2Buy

02-10-06, 06:38 PM

John -
The grill cloth is just fine, but the polyester batting is an unknown quantity. There is no density information given, and without that I don't know the absorption. Generally, when you pack light polyester batting to make it denser, it will "pillow out," and create an unsightly bulge.
Regards,
Terry

Thank you Terry.

It's becoming apparent to me that most sellers of polyester batting don't even bother to report their densities. Having said that I have found densities from 3 oz to 20 oz. Will all of these work equally well?

I have also seen a post from John Risch stating that we should be using "high loft" batting 0.5"-0.75" thick. I don't know why he said that, he doesn't explain it.

I guess I should say that my goal with the polyester batting is not to improve the absorption but primarily to prevent the fiberglass dust from getting outside the trap. I too have young kids running in the house.

Best,

John

jimsiff

02-10-06, 07:01 PM

Jim -
Acoustic cotton has about the same flow resistance as fiberglass of the comparable density, which is to say it has comparable absorption. Mineral wool has significantly more flow resistance for the same density as the other two, which means it has somewhat different absorption. I don't have measured coefficients for mineral wool this thick (don't think it is sold in 100mm thickness), but it should reach slightly lower in the lowest bass (maybe <50 Hz), quite possibly at the expense of higher bass frequencies.

Regards,
Terry

Terry,

Thanks for the response. I have decided to negate the mineral wool from the equation due to the different absorption characteristics, and I found a local supplier of unfaced 703 for a reasonable price.

Does anyone have any thoughts on my other questions? I quoted my previous post for reference:

1) For my corner traps, I want to use a 8' 4" thick panel across the corner, or a "super chunks" style trap. Would I gain a lot of absorption by going with the "super chunks" style trap?

2) Would acoustical cotton be better than fiberglass for a kid friendly environment? I plan on covering whatever I use with grill cloth or muslin.

4) The first reflection points for my L/C/R speakers are mostly covered by the back of the couch and loveseat. There is about 1' between the top of the couch and the shelf at 4'. Would I be okay just putting the absorption panel on the shelf, or should I make a 1' tall absorber to treat that small area as well?

Thanks and regards,

Jim

Terry Montlick

02-10-06, 07:14 PM

...
I guess I should say that my goal with the polyester batting is not to improve the absorption but primarily to prevent the fiberglass dust from getting outside the trap. I too have young kids running in the house.

Best,

John
Then I would go with acoustical cotton, John.

Regards,
Terry

Ready2Buy

02-10-06, 07:57 PM

Then I would go with acoustical cotton, John.

Regards,
Terry

Terry,

Unfortunately, I already have purchased a ton of fiberglass boards. (They are stacked out in the back yard) I just have to find the right material to seal these traps. As last resort I might consider wrapping them in thin plastic bags.

Best,

John

jimsiff

02-10-06, 09:46 PM

Terry,

Unfortunately, I already have purchased a ton of fiberglass boards. (They are stacked out in the back yard) I just have to find the right material to seal these traps. As last resort I might consider wrapping them in thin plastic bags.

Best,

John

John,

I would wonder whether or not the plastic bag approach would reflect mids and highs too much for your 1st reflection panels? The plastic would certainly be sealed and fairly durable.

I'm thinking aloud here, so discard any ideas you don't think will work. I wonder if you could effectively seal the surface of the fiberglass with some 3M spray adhesive before applying the fabric wrap. Or, there was some fiberglass panel edge sealer manufactured by JM that might reduce or eliminate loose fibers. You could also experiment with wrapping the fiberglass inthin tissue paper or florist paper (http://www.papermart.com/index/index_retail_tissue.htm) using 3M spray adhesive to hold it in place before wrapping it in fabric. I would think that would be more acoustically transparent than plastic, but I'm not really sure.

I'm thinking of making panels for the corners using 1x6 frames, and 4" of unfaced 703 sandwiched between a layer of cotton batting, then wrapping the cotton/fiberglass and frame with cheap muslin fabric. The frame, cotton, and fabric should do a decent job of sealing the fiberglass from prying little fingers. For the walls, I'm thinking of doing 1x4 frames with 2" of 703 between cotton batting and muslin.

I could always go with acoustic cotton, but I would want to find a local supplier to reduce shipping costs. There seems to be a significant premium as it is for cotton vs. fiberglass.

bpape

02-11-06, 10:48 AM

Absolutely. If you wrap the fiberglas in bags, you'll defeat their purpose as reflection absorbers. Your options are:

1. Put some batting around them that will hold things in but not significantly change their absorbtion characteristics.

2. Sell the fiberglass (should be easy - always people looking) and use acoustical cotton.

Ready2Buy

02-11-06, 11:56 PM

Guys, I appreciate your input but I think I made up my mind. I am not going to wrap the fiberglass in plastic bags and I am not going to trade it for acoustic cotton (I bet getting cotton will probably be even harder). I have done enough work already to acquire my fiberglass.

I am going to use 1/4" thick polyester batting on the fibeglass and then frame and wrap speaker grille cloth over it. If we all start itching after I place the traps in the room I will know what to do. :D

Jim:
If you are building 4 inch thick traps then your 1x6 frames should work fine. You would however be blocking the sides of your fiberglass material with your wood frame. That's an additional 8"x96" of blocked surface area that could be used to absorb even more sound. In my case I'll be using 10" thick traps (five 2-inch boards placed back-2-back) and I want the sides of the traps to be exposed to the sound field. I will probably go with 1x2 front frame and 1x2 back frame with the two attached together using 10" long 2x2 strips. This should let sound come inside the traps from the sides as well as the front and back.

Best,

John

air2mag

02-12-06, 01:35 PM

I could sure use everyone’s help. I have been reviewing posts for the last six months and have finally worked up the courage to start my theater room. The room is approximately 13 X 19 and is located in the basement (7 foot ceiling). Currently the room is finished in wood paneling. Two of my walls are outside basement walls with 2X4 studs, rolled insulation, and then the paneling over the concrete. The front/screen wall is also 2X4 framing with insulation sandwiched between the paneling and chip board which is in the laundry room. The four wall is pretty much taken up by the stairs. I plan to cover all the walls with GOM. Since my room is already on the small side, I am thinking of removing the paneling and using the existing wall studs for my framing. I plan on using OC 703 and batting as many other have done. I know the 2X4 framing will leave a space of approximately 3 ¼”, but I think with the insulation already installed and the 703 it should be just about right. If not, I could always add some batting to make up the difference. I know this is not the optimum solution, but it seems better than going to all the work of adding furring strips over the paneling. Anyway, you all are the experts, what do you think?

pandasys

02-12-06, 01:40 PM

Ready2Buy

02-12-06, 10:16 PM

Not trying to change your mind, but getting the cotton is easy. See bpape's homepage.

Well it's best to get the material locally to avoid transportation costs. But I did look at bpape's site and he sells 2"-thick cotton for about $28 a piece. I bought 2"-thick fiberglass for a little under $8 a piece. In the quantity I wanted, I am not ready to pay 3.5 times more for the material.

Best,

John

simon_templar_32

02-13-06, 08:46 PM

bpape

02-14-06, 09:15 AM

I certainly understand John. Just a couple of clarifications.

1. That price is for 1 single piece.

2. For bass control, there are other products that are considerably more cost effective. The 2" 3lb is primarily sold for reflection point usage.

Terry Montlick

02-14-06, 09:29 AM

ebr

02-14-06, 01:52 PM

Not a stupid question at all. This actually works! It comes down to an aesthetic call. If you don't mind a piece of absorber hanging off the top of your speaker, then go for it.

- Terry

Wow, what a great idea - especially for those of us who's speakers are hidden behind fabric walls.

J-dubb16

02-14-06, 02:36 PM

bpape

02-14-06, 02:40 PM

Just be careful when behind a wall. To avoid reflections off the false wall framing you want the speakers pretty close to the fabric. That would likely not leave enough space for sufficient overhang to deal with the vertical reflection on the ceiling.

To figure what you'd need....

If your speaker tweeters are at about ear level, then the reflection on the ceiling will be basically halfway between you and the speaker along a straight line from tweeter to ear. Transfer that to the ceiling (do this all on paper). Then, look at how far up from the tweeter the cabinet top is. Do the trig for that little triangle using the angle established before and the height difference and it should give you the distance out to cover the line from tweeter to reflection point on the ceiling.

Hope that made sense.

Terry Montlick

02-14-06, 02:52 PM

That is an awesome solution for hidden speakers. How would we calculate the length the absorber would overhang.
Another way is a variation on the classic mirror method. With an assistant, place a mirror on the ceiling at the spot where you can see tweeter and midrange drivers reflected in the mirror from your theater seat. Then, just extend the absorber forward until it completely hides the drivers' reflections in the mirror.

Regards,
Terry

Ktulu_1

02-14-06, 03:07 PM

Mirrors on the ceiling? Is this the "How to Acoustically Treat Your Bordello" thread? :D

LarryChanin

02-14-06, 03:07 PM

Hi Guys,

Not to be a party pooper, I think this may be more difficult to achieve than you think even if your speakers are hidden behind fabric.

Attached is a drawing of the profile of my room. The drawing focuses on ceiling reflections from the upper center channel speaker. The situation would likely be more problematic for lower speakers such as the mains because the reflection points on the ceiling would be further into the room and would require great amounts of overhanging insulation.

You'll notice that even for the first row of seating, with an upper center channel close to the ceiling, the amount of absorber sticking out to block the first reflection point would put it outside the fabric shadowbox.

Terry: One other question. Even if we could conveniently locate a blocking piece of insulation, wouldn't the edges of the insulation introduce diffraction which would reintroduce the early reflections we were trying to avoid?

Larry

ebr

02-14-06, 03:16 PM

I think you're right, Larry. The absorber would probably have to stick out too far to be practical and, If you got the absorber overhanging enough it might also block some direct sound from certain positions.

As Rosanne Rosannadanna would say...

LarryChanin

02-14-06, 03:43 PM

That is an awesome solution for hidden speakers. How would we calculate the length the absorber would overhang. I would assume that an angular measurement from the speaker cone to the absorber would be needed. But what angle is typical and is it from the tweeter or midrange driver or both?

J-dubb

Hi,

As bpape described we can calculate the reflection points, then position he absorber to intercept the reflection point. If you recall we described the calculation in your Reflection Points thread (http://www.avsforum.com/avs-vb/showthread.php?p=6917872&&#post6917872).

In addition to all the tweeters (some speakers have more than one) we would also need to deal with all the midrange drivers locations. If your seating reclines this would introduce additional complexities since each driver-seating position combination would result in a different ceiling reflection point. The placement of the absorbers would have to handle all the resulting reflection points.

Larry

Terry Montlick

02-14-06, 03:48 PM

Mirrors on the ceiling? Is this the "How to Acoustically Treat Your Bordello" thread? :D
What have you got against a Theo K. theater? :D

Larry -

You won't get significant diffraction unless you use a hard frame for such an absorber. Also, any diffracted sound will be spread out, and should be at a lower amplitude in any direction than specularly reflected sound from the ceiling.

In any case, I think this technique would only be practical for a first row of seats.

- Terry

LarryChanin

02-14-06, 04:22 PM

Larry -

You won't get significant diffraction unless you use a hard frame for such an absorber. Also, any diffracted sound will be spread out, and should be at a lower amplitude in any direction than specularly reflected sound from the ceiling.

- Terry

Hi Terry,

Thanks for the response.

No doubt the density of the chosen absorber and its proximity with the tweeter will also determine whether or not we are introducing diffraction problems.

Recently I've been experimenting with those rings you place near tweeters to reduce diffraction. I was hoping to do essentially what simon suggested, but by placing the absorber very close to the tweeter I hoped to avoid the problem I described regarding large amounts of overhanging absorber.

I then measured the frequency response before and after the placement of the absorber. I found that more often than not, for very close placement, this resulted in either hurting the frequency response, or yielded an insignificant change (less than .25 dB). I reasoned that the negative effect on frequency response was probably due to the introduction of more reflections due to diffraction rather than reducing the reflections that were hitting the ceiling.

Larry

Stima

02-14-06, 06:29 PM

Ethan,

I have a quick question regarding the OC703.

If you recall I planned the following:
Mid\High Wall treatments: 2" OC703 covered in any "breathable" cloth. Floor to ceiling treatment of the "three sides" of my front wall behind the screen, and both side walls just past first reflection. Don't want foil covered OC703 as it refelcts hi's. I also plan to treat the bottom half of the rest of the side walls with OC703 and the entire (floor to ceiling) back wall. The top half will use 1" batting covered by an acoustically transparent cloth (GOM 701). I don't plan to put anything on my ceiling and have thick burber carpet on the floor.

However, after re-re-re-re (you get the point) reading this thread, I believe I still don't have everything correct.

According to some of the very first posts in this thread by yourself and D.E., I should NOT treat the side or back walls from floor to ceiling EVEN at the first reflection points. Rather, I should treat the side and back walls from floor to ear height and then batting above. Also, I should use 1" OC703 NOT 2" everywhere.

If you can't tell, I am ordering my OC703 TOMORROW and really want to get it right.

Thanks for any help here!!
Dan

bpape

02-15-06, 07:34 AM

Dan,

I think the issue is that with the front wall and first X of the side walls covered floor to ceiling in 2" material, covering the rest of the walls with a mix AND the whole rear wall floor to ceiling would make it too dead and unbalanced (though better than 1" everwhere).

There are several different schools of thought on how to treat a room. They can use very different methods to achieve the same end. The goals are:

- Get the bass under control (nothing you've adressed above will do that)
- Tame the early reflections
- Kill the front wall
- Get the decay time for the space under control relatively evenly across the board. The target time to shoot for is dictated by your room volume.

Now, HOW you do the above, is up to you. Sounds to me like you're trying to mix a couple different methods and it's not working out well.

SC Bones

02-15-06, 09:35 AM

WOW This site is great...something happen to my last post so I will post again....I have a 1200 sq foot basement...I have been looking for help w/ a home theater for MONTHS, until three days ago, when i found this site!!! You guys have tons of pics AND knowledge.....Estimates for a home theater run $30,000 but some of you have spent 1/2 that!!!

Soooo I am thinking about doing most of the work myself....My question is.....is a home theater hard to plan and build....I have most of the tools.....I'm just a little scared to get started.....I have a space in my basement that's 25 x 13'6...I would like to have a 100 maybe 110 inch screen, and two rows of four chairs...do you guys think this room is big enough???? I am concered that I will not be able to get a row of 4 theater chairs w/in the accross 13'6''

bpape

02-15-06, 09:42 AM

Don't be scared - there are plenty of people here who will help. I'd recommend starting your own thread with a sketch of the space and what you want to do. Planning is the critical part. Don't get ahead of yourself. Know your goals and plan ahead.

Stima

02-15-06, 10:38 AM

bpape,

Thanks for the reply.

I think I have decided upn the following:

Front wall: 1" 703 mounted to 2x4 stud wall with R12 binsulation between studs. (no drywall between 703 and R12)

Side walls: floor to ceiling 1" 703 up to fst refelction for both rows of seating. (will be about to first row actually)

Side walls cont': after first row, will cover up to ear height with 1" 703. Upper "half" will be filled with 1" thick, 10oz batting.

Rear wall: Same as side (cover up to ear with 1" 703)

Sofits: Bottom covered with 1" 703

Bass trapping: Straddle rear corvers (24" surface area from floor to ceiling) with 4" 705 (or 6" 703 if 705 is not available)

Bass trap cont: Behind AT screen\wall, two stacks of rolled R12 (still in wrapping) from floor to ceiling.

I am hoping all this 703 doesn't result in too dead a room and teh bass traping will be sufficient.

A couple side notes: The walls and ceilings are "floating" and completely seperate (secondary) from exterior walls\upstairs floor joists, however they only have 1 layer of drywall. My idea was to "decouple" the room while still providing "fleixable" enough walls to reduce room modes. Also, my back row is only a couple feet off the rear wall, so diffusion is not an option.

THE_COW_IS_OK

02-16-06, 03:12 AM

Now I know this is probably a stupid question, so don't jump all over me. Suppose I am trying to control the ceiling reflection. What is wrong with putting a piece of foam (or acoustical cotton, etc.) on top of the speaker cabinet but jutting out front a bit to catch the wave before it even gets to the ceiling?

Unlike general concensus here, I don't think this is a good idea. having any solid surface near the speakers drivers will affect air impedence and will create bass boost at some frequencies.

Do this experiment:

surround your speaker with 4 rigid fiberglass panel. 1 on top, 1 on bottom, 1 left, and 1 right. you won't need any SPL Meter to nitice the difference in bass even if you sit very close to the speaker.

THE_COW_IS_OK

02-16-06, 03:22 AM

Another side effect is diffraction in mid-high frequency. Even when using non-wooden frames. Speaker design factors in cabinet construction as the only object surrounding the drivers and thus they are opimized for that. Any other object coming close to the drivers, will affect performance.

bpape

02-16-06, 07:30 AM

Stima,

That is a lot and there are some things I'd not do - like the no drywall on the front.

Maybe you should start your own thread to discuss.

bpape

02-16-06, 07:33 AM

air2mag,

Sorry your question got lost in the shuffle. You might want to start your own thread on this - there will be a lot of different input.

Bryan

air2mag

02-16-06, 08:26 AM

Thanks Bryan I will give that a shot.

Mike

myfipie

02-16-06, 10:02 AM

Terry Montlick

02-16-06, 10:13 AM

Stima,

That is a lot and there are some things I'd not do - like the no drywall on the front.

I ditto Bryan.

- Terry

Stima

02-16-06, 10:54 AM

Terry, Brian...I started my own thread. "Load, Aim, Fire...'

Please feel free to elaborate on anything you don't like in the setup.

I am ALWAYS open for suggestions.

Thx,
Dan

LarryChanin

02-16-06, 11:38 AM

Soooo I am thinking about doing most of the work myself....My question is.....is a home theater hard to plan and build....I have most of the tools.....I'm just a little scared to get started.....I have a space in my basement that's 25 x 13'6...I would like to have a 100 maybe 110 inch screen, and two rows of four chairs...do you guys think this room is big enough???? I am concered that I will not be able to get a row of 4 theater chairs w/in the accross 13'6''

Hi,

I think that if you are planning for typical sized cinema recliners that your width dimension will make it difficult to fit four seats across. For example, my four Jaymar recliners are a little narrower than the wider Berlines at a total width of roughly 10 feet, versus 11 feet 5.5 inches for the Berkines (model 90).

Here's a drawing of my configuration in a room that is 15 feet wide.

http://mysite.verizon.net/res8ycu4/sitebuildercontent/sitebuilderpictures/plan.gif

You'll notice that I had to shift the seating to the left to provide a wider single isle on the right. You should also try to get as much distance as feasible between the seating and wall to reduce boomy bass problems.

If by "theater chairs" you mean ones like this (http://www.htmarket.com/forumrocker.html), four of these would be about 8 feet wide. So you should be able to fit four of this type of seating allowing two isles of about 2'9" on either side.

Larry

Phil Olson

02-17-06, 03:15 AM

Well, I finally finished reading the entire thread :eek: and one thing I noticed is that there is a general consensus on a balanced absorption through the frequency range, but since everyones room is different, the advice given here is really more of a very rough guesstimate, the true test being measurement and tuning.

When the insulation stuffing begins, etf Acoustics, ($150), can measure RT-30, RT-60, etc. and allow you to know exactly what needs to be done.

Even though this tool costs some coin, there is really no substitute for knowing where you are vs guessing.

Instead of asking "I've installed 10 panels of xyz insulation on the wall and put 2 abc base traps in the corners, what else do I need to do?", the person could just attach his etf graph and that would point to exactly what needs to be done, (more bass traps, less high end absorption, etc.).

Specifically, what I am advocating is that the first bit of advice to give to people embarking on a theater construction project is to pick up at least etf and a cheap mic.

Of course if one is on a seriously tight budget general advice is better than nothing, but if there is room in the budget for insulation, framing lumber, speaker cloth or GOM, etc., spending a little on a tool that tells you when to stop is a small price to pay. It could easily pay for itself by allowing one to apply just the right amount of absorption in the right places.

So am a nuts or what? :D

BasementBob

02-17-06, 04:59 AM

Phil Olson:

Ignoring noise floor, soundproofing, video, seating, HVAC, bells and whistles...

ETF5 is a tool. The trick is to know how to read the graphs, and how to do tests (mic placement, gate times, etc) to get graphs that are easy to interpret. Without correct interpretation, a lot of the information on the graphs is not helpful. Without correct tests, correct interpretation is impossible.

I think the best place to start for anyone is Master Handbook Of Acoustics (http://www.amazon.com/gp/product/0071360972), and learn what RT60 and SBIR and so on are.

Thereafter there are four types of rooms depending on WAF restrictions
1) a few early reflection and flutter controlling absorbers scattered about the room (DIY, semi-DIY bags, pre-manufactured)
2) corner traps (with or without #1 due to windows etc) - very effective in an otherwise empty room
3) DIY whole 9 yards acoustically - Able to cover any amount of the room surface (e.g. 60% of the room surface) with acoustic treatment. Able to figure out ETF5. You're way beyond corner traps and purchased absorbers if you're doing this.
4) Hire professionals (DE before the room is built, eor Terry after the room is built).

If you're considering #3, then the second book to buy is How to Build A Small Budget Recording Studio From Scratch : With 12 Tested Designs (http://www.amazon.com/gp/product/0071387005).

Knowing the possibilities (the book MHOA, and others), and knowing what you hear (problems, boomyness, missing frequencies, speach inteligibility, imaging, spaciousness, sweet spot, flutter, etc), and knowing what problems ETF5 detects at the listening position (first test) in details that you don't hear, and knowing how to conduct tests to identify the problem that's causing the anomoly and the limits of ETF5, then knowing how to treat it economically (speaker placement, listener placement, room size and shape, absorbers (porous, membrane, helmholtz), inter-absorbtion effects, diffusers, reflectors, couplers, EQ, etc).

BTW, if you're going to buy ETF5, you might as well pick up their calibrated microphone.

Ethan Winer

02-17-06, 02:02 PM

Phil,

You definitely get it, and I'll add just one point:

> etf Acoustics, ($150), can measure RT-30, RT-60, etc. <

It turns out that ETF is not very useful for measuring reverb time. Doug Plumb, ETF author, told me he'll have RT measurements in his newer, more sophisticated, R+D program soon. I think he might even have added that to R+D yesterday. The good news is that anyone who buys ETF gets R+D for free.

--Ethan

mtmason

02-20-06, 12:28 PM

I've been reading.. a lot... of this thread and been inspired to tackle some accoustic treatments to my Home Theater/Family Room. When I went back to my room to listen with a more critical ear I instinctively turned off my projector, because it was distracting me from really listening to the "room." Then I realized, what did I just do? Maybe I should be starting with silencing my projector (IF 7200). It's not terribly loud, but definitely adds a high frequency sound to the room from mostly the fan and also the color wheel.

I prefer to focus on one thing at a time. Does it make sense to start with a hush box as my rooms most effective accoustical "treatment." Are the typical improvements to a room by adding bass traps and first reflection treatments usually so dramatic that they over shadow noise introduced by a projector? I know a lot comes down to how bad my room sounds now and personal preference, but I'm interested in people's opinions here and wonder for all the talk about sound isolation from outside the room, HVAC, etc... I haven't seen anything about addressing projector noise (could have easily missed it).

Also, what would be the best type of accoustical material to line a hush box with? Thanks for your opinions.

MM

ebr

02-20-06, 12:35 PM

...Are the typical improvements to a room by adding bass traps and first reflection treatments usually so dramatic that they over shadow noise introduced by a projector?...

Yes.

That is not to say that a hush box won't do you good. I have no idea how much noise pollution is being introduced there, but, proper room treatments, imo, are one of the best, and least expensive, improvements you can make to your audio system.

Ready2Buy

02-20-06, 09:11 PM

This past weekend it rained pretty hard here in beautiful Southern California and even though I had covered the fiberglass with a tarp, a small amount of water still managed to get through it as well as the plastic bags that the fiberglass boards are wrapped with. Today the sun came out and I removed the tarp and relocated the material to a dry spot in the back yard. I am hoping that the sun will dry out the material in a few days but I have also heard that once fiberglass gets wet (even a little) it poses the risk for mold. Is this true?

Is it pointless to expect to dry-out the material or should I just throw away the bottom few boards in the pile that got wet the most?

Thanks guys,

John

myfipie

02-21-06, 11:57 AM

John,

You can try to dry it out, but I hate to tell you but it probably is trash! Trust me you will smell it if it does not dry out..

Glenn

Westshorestudios

02-21-06, 04:42 PM

Ready2Buy

02-21-06, 07:52 PM

Can you soak the wet area in bleach, then put out in the sun? the bleach should kill any mold spores, then you'll just have to let the chlorine smell dissapate.

How thick is the fiberglass and how dense?

They are 2'x4' boards, 2" in thickness, 3 pounds per cubic foot in density. (The brand name is Johns-Manville Insul-Shield IS-300.)

Only the bottom four panels in the pile of 63 look like they are affected because they have a little bit of a rusty looking color in spots. I opened the plastic yesterday and expose the boards to the open air and the sun. This afternoon they look pretty dry except for this discoloration on those four boards. They don't smell though and I put my nose one inch from the boards.

You think they are still good? I mean should I still pour a galon of bleach on them or should I just toss those four?

Thanks guys, I appreciate the advice.

John

lakeeliza

02-22-06, 12:16 AM

Is there an alternative product to Green Glue? Thank goodness they are around and seem to be half the cost of Quiet Rock. Still, the price is way beyond my budget. It seems that Viscoelastic glue, is Viscoelastic glue. Is this correct, or is Green Glue something special? I see that 3M makes it, car manufacturers use it, and others have it under other names. This discussion group seems to only talk about Green Glue and wonder if there is anything else out there.

Thank you,
Rick

myfipie

02-22-06, 08:48 AM

They are 2'x4' boards, 2" in thickness, 3 pounds per cubic foot in density. (The brand name is Johns-Manville Insul-Shield IS-300.)

Only the bottom four panels in the pile of 63 look like they are affected because they have a little bit of a rusty looking color in spots. I opened the plastic yesterday and expose the boards to the open air and the sun. This afternoon they look pretty dry except for this discoloration on those four boards. They don't smell though and I put my nose one inch from the boards.

You think they are still good? I mean should I still pour a galon of bleach on them or should I just toss those four?

Thanks guys, I appreciate the advice.

John

All you can do is try, but with that said I have read a lot of posts that talk about a mold smell after getting wet.. Hate to see you waste money but just pointing it out to you.. :(

Glenn

Westshorestudios

02-22-06, 10:08 AM

I haven't had to deal with the wet fiberglass issue, so take this for what its worth.

Just because a fiber based material gets wet doesn't mean it's ruined or will grow mold and mildew. We wash clothes every day. We then dry those clothes. no problem. Even when we leave the clothes in the washer wet for a couple of days days, and then dry them, no problem.

Your fiberglass boards, if they got a little wet but the next day you put them in the sun to dry, i don't see how they will develop a mold / mildew problem.

Also, mold / mildew spores are everywhere: in our houses, floating in the air, in our cars, in our carpets, in our closets, on newly purchased rigid fiberboards, etc. If, after your boards dry and bake in the sun for a few days, you don't smell mold / mildew mustiness, I think you are fine, even without pouring bleach on them.

Before using bleach, I would test a 1'x1' piece by pouring bleach on it and letting that dry and the bleach / chlorine evaporate. My biggest concern would be a lingering bleach smell.

I just hate to see you throw those fiberboards away for no reason.

Just my .02.

Good luck.

myfipie

02-22-06, 10:24 AM

You are totally right you can dry out fiberglass, but you have to make sure it is totally dry.. Problem is if it is moist at all then you rap it, you get into problems...
Just give it a few days out in the sun and see how it goes.. I would take them in at night because of morning dew.. :)

Ready2Buy

02-22-06, 10:28 AM

If, after your boards dry and bake in the sun for a few days, you don't smell mold / mildew mustiness, I think you are fine, even without pouring bleach on them.

I just hate to see you throw those fiberboards away for no reason.

WestShore,

Thanks for the advice, I am gonna leave them out there in the sun for another week and if there is no odor by then I'll build them into bass traps. You make a lot of sense my friend

Glenn:

I hear you as well and you may eventually turn out to be right but I am not sure yet that these boards can't be saved. They have been drying out nicely.

Best,

John

myfipie

02-22-06, 10:54 AM

I will say that you are out on the west coast so you do have more dry air.. Heck yes a week should do it... If you lived in Florida I would say "sorry charley"! :)

Glenn

dknightd

02-27-06, 09:52 AM

Great thread. I finally made it to the end - yea!
I think all my questions, for now, have been answered.
I'm just posting to subscribe to the thread - couldn't see
another way to do that - probably my mistake.
Anyway, caryy on, and thanks . . .

Ktulu_1

02-27-06, 10:06 AM

dknightd, if you click "Thread Tools" on the top or bottom of each thread you can subscribe to the thread and get an email when someone posts to it.

rmlowz

02-27-06, 06:15 PM

Ready2Buy

02-27-06, 07:36 PM

Regarding treating the FRONT wall with absorption:

A large projection screen looks great when it's attached directly onto the front wall but how do you treat the first reflections? (can't put fibergalss panels infront of the screen)

I would like to use a fixed-wall screen if it wasn't for the above problem. The alternative is to use a ceiling mount placing the screen about 6" infront of the front wall. Then I can hang fiberglass panels in the 6" inch space between the projector screen and the front wall.

Only problem is that the ceiling mount looks a bit amateurish. Is there a better option?

Eldoradophoto

02-27-06, 10:27 PM

Hello,

What product can be placed in a room to make it not as bright sounding . Is there a simple solution that can be bought and placed in corners or walls? The room is 15x19 and is already being used as a movie room. I appreciate your help.

rmlowz

This question has a lot of answers. I am not the expert on this, but would refer you to posts in this thread by bpape, and others. If you start reading at the beginning of the thread you'll read a lot about OC 703 (i.e., rigid fiberglass), linacoustic, and other mineral wool type products that can be placed in the corners for bass traps, placed on the walls to absorb at first reflection points, and others. You will likely get more people chiming in if you read this thread and then ask more specific questions oriented toward you're specific situation or to clarify your understanding of the material already posted, since this question when phrased this broadly has been covered pretty extensively.

bpape

02-28-06, 07:29 AM

Eldorado is right on the money. Kill 2 birds with one stone by using something soft as a broadband absorber in the corner that will also double for bass control.

To get additional taming, you'll need to address your reflection points - which will NOT be in the corners but are important to cover.

As for treating the front wall, you can still use a fixed screen and still treat the front wall. Do the whole thing. Most screens still have 1-2" behind them. Having some absorbtion behind will not deal much with the highs but will still help in the mids and upper bass a bit and help to focus vocals.

tonybradley

02-28-06, 08:43 AM

I did the mirror test for first reflections last night. I did it for all six seating locations (3 in front, 3 in rear). Based on the test, I will need absorption from about the from speakers to the first row. I had originally hoped to make panels and space them out on the wall for a nice clean look. However, they will now have to be butted up against each other (4 Panels) and not sure how good that will look. I've been playing around with some ideas and here is what I'm thinking.

Start the first panel quite low, the next panel a little higher, and so on. Step configuration. I don't care for the horizontal look. Is the goal to be sure the Panel covers the height of the drivers on the speaker? Since I may do the Step approach, will I be good as long as the drivers are covered?

Second Option: Makie a frame that is 8feet long by 4 feet high and inside the frame, place four rigid fiberglass panels side by side and cover with the fabric. I realize this would result in a HORIZONTAL panel, but it would be much bigger. I think I would get better absorption this way as I wouldn't have multiple frames (sides of the frame being reflective) to contend with. Would this still work by butting the fiberglass boards up against each other in one large frame?

bpape

02-28-06, 09:41 AM

Either will work. Just make sure you're covering the mid/tweeter height.

I've seen people do the 1 big panel and then sew designs from a couple different colors, like maroon diamonds on black background or the opposite to give it some interest. That way it doesn't look like a monolith.

As for 1 or more frames, sometimes you can use them to your advantage. Many narrower panels (like 6" or so) spaced out can act as both an absorber and provide some diffusion. All you're really looking for is to not have a direct bounce to your ear from the side walls. If a point falls on the side of a frame, then it's going to bounce back off the wall and toward the front again - mission still accomplished - assuming you've deadened the front wall so it will get absorbed there.

tonybradley

02-28-06, 10:46 AM

tonybradley

02-28-06, 11:24 AM

Bryan,

I remember I quickly asked you this question months ago, but can't remember the reason you said this may not be a good idea. After hanging my panels, I was thinking of cutting out a diamond from a piece of 2" OC703, wrapping it, placing velcro on it and the large panel and sticking the diamond in the center to give it a Three Dimensional Look. What would the CONS to this approach be?

bpape

03-01-06, 11:15 AM

That would work OK. The only problem is that getting 703 to be wrapped tight so you have nice clean edges can crush the edges. 705 is stout enough to handle it. Or, you could do the drywall corner bead frame thing as it doesn't add much weight and will give you a nice clean look.

tonybradley

03-01-06, 12:04 PM

LLA2

03-02-06, 08:01 PM

Hello all,

Excellent forum btw.....

I have a typical plaster room measuring 15'x28'x8' that I'd like to turn into a HT, and was wondering if the techniques for treating an existing room are the same as those mentioned on this forum for new construction?

Any advice will be greatly appreciated.

Thanks

tony

bpape

03-02-06, 09:09 PM

Welcome to the forum. The answer is somewhat YES and somewhat NO. There are SO many topics that have been covered in this thread that it's hard to address everything that may and may not be the same.

I'd suggest starting your own thread and asking some more specific questions with a description of your space included.

unclebooboo

03-03-06, 04:37 AM

Hi,

Is it possible to cover the front wall with wood paneling for aesthetics or does that entirely ruin the whole point of covering it first with absorption panels? Also, I want to cover all of the side and back walls with faux suede fabric over the absorption panels and polyester batting, but does that also ruin the intended acoustic effect?

Thanks,

Bruce

unclebooboo

03-03-06, 04:39 AM

Does anyone know of a quality acoustic testing service in Salt Lake City?

Stima

03-03-06, 08:38 AM

As the foremost expert in sound absoportion I would say....oh wait, I am just a beginner like you!!! ;)

Actually, the front wall treatment varies between two camps. Dennis says the entire wall NEEDS absoprtion making hard paneling impossible. However, I believe either Ethan or Terry claim front wall absoption is NOT necessary, making paneling o.k. So, you get to choose whom to believe.

For the side and back walls: Suede is not even CLOSE to acoustically transparent making whatever you put behind it for absorption nearly useless. I am sure SOME mids and highs will penetrate teh suede and be absorbed, but not nearly as much as would be with an acoustically transparent cover.

Now, all that said to say this: It's YOUR theater. This is a forum of self proclaimed experts. Do what makes YOU happy...not any of us. If the sound isn't PERFECT but you LOVE how it looks and can compromise the two in your head....then DO IT. Don't let the idea your theater has to have audio perfection stop you from enjoying your hard work!!

BasementBob

03-03-06, 08:50 AM

unclebooboo:

Any fabric you can breath through will have no effect on the absorbtion. If you can't breath through the fabric, then it depends on the fabric (vinyl and leather would reflect high frequencies, velvet would absorb high frequencies).
Any fabric you cover the walls in should be fire rated or fire retardant treated.
4x8 wood paneling will reflect mid to high frequencies, and probably the lows too. So, covering absorbtion with wood is well, building a reflective wall.

I like to say I'm not an expert - I give ideas not advice.

unclebooboo

03-06-06, 02:26 AM

Thanks for the responses.

I have seen a design that uses fabric panels for the speakers and additional design elements with paneling trim, that should make a good comprimise for me for aestetics and acoustics. I will check the fake suede to see if I can breathe through it, but I suspect I will have to switch to fabric even though it decreases that warm feeling I am looking for.

Thanks again.

bpape

03-06-06, 07:15 AM

Bigsmith

03-06-06, 12:13 PM

Three of the four vertical wall corners in my theatre have doors in close proximity and thus will not accomodate the typical corner bass trap configuration. I know the tri-corners at the junction of two walls and ceiling can be used, but in my case these are compromised as well.

Do fiberglass panels oriented horizontally to bridge the corners where the walls meet the ceiling (around the perimeter of the room) work as bass traps?

Stima

03-06-06, 12:21 PM

Yep, wall to ceiling and wall to floor junctions are both prime places for bass traps. You can pretty much treat as much ceiling to wall intersection as possible and not hurt the sound in the room.

Go with MORE 4" OC703\705 panels (or 4x1") as opposed to less\thicker panels.

Stima

03-06-06, 12:23 PM

Don_Kellogg

03-06-06, 01:47 PM

Ethan Winer

03-06-06, 02:06 PM

Don,

> I have 12 large wedge bass traps from Aulex, I plan to use them in the corners to help with Bass. Is this too much <

Too much? It's probably not enough. :D

--Ethan

stromand

03-06-06, 02:44 PM

Well, let's take a quick time out here. Just breathing through it (relatively easily), while OK for a quick test to put in front of treatments is not enough to assure it will be acceptable in front of a speaker.

Agreed. Breathable doesn't guarantee acoustical transparency.

Come on guys. For the education of the home theater novice please post the answer, not more of the question. I have read more than once in this forum that "breathing through it" is a test for acoustically transparency. Now you both say it isn't without qualifying what is. I am not looking for third party lab verification of your answers but how about a little more detail.

I have been to fabric shops and tested materials I am considering for acoustical treatment covering, curtains, corner bass trap covering, etc., and I have breathed though countless materials with varying degrees of ease/difficulty. My standard has been the closer the material is to speaker cloth the more acceptable it is. But I am prepared to compromise a little for aesthetics. The question is how far should I go?

Joel DuBay

03-06-06, 02:46 PM

I currently have 48 Aulex 2" 2x4 foot wedge panels can I use these acoustic panels on side and front walls in place of the owens, and other insulation that has been mentioned in this thread. Also I have 12 large wedge bass traps from Aulex, I plan to use them in the corners to help with Bass. Is this too much, What if I use the 2" on the front wall and then put the bass traps in place as well.

Hey Don, that sounds like a good start! Auralex is a well known, very good product for some applications.

Could you list your room dimensions and any structural anomolies you might have in said room? Would love to help you out and make sure you are getting what you "need".

Cheers,

Joel DuBay Sr

Joel DuBay

03-06-06, 02:55 PM

Come on guys. For the education of the home theater novice please post the answer, not more of the question. I have read more than once in this forum that "breathing through it" is a test for acoustically transparency. Now you both say it isn't without qualifying what is. I am not looking for third party lab verification of your answers but how about a little more detail.

I have been to fabric shops and tested materials I am considering for acoustical treatment covering, curtains, corner bass trap covering, etc., and I have breathed though countless materials with varying degrees of ease/difficulty. My standard has been the closer the material is to speaker cloth the more acceptable it is. But I am prepared to compromise a little for aesthetics. The question is how far should I go?

Agreed Dave.

The "breathe" test is a standard, albeit non-scientific way of determining if a material is NOT breathable, more so than to determine if it is "breathable". Many fabrics are NOT breathable/ transparent in the acoustical sense. Thick canvas is NOT breathable in the acoustical sense, but, it doesn't (for instance) impede the ability to affect low feequency sound waves when used as a bass trap (only) cover. For speaker covers however, a material must not just be "breathable", it must be VERY easy to breath through. Thin nylon (such as stocking material) is a very breathable fabric, especially when stretched. Grill cloth is "breathable". And as such, this is the standard by which other materials are gernerally judged. In a non-scientific world, I believe as you do, that the more a fabric acts (when breathed through), like speaker cloth, the more likely it is going to work for said purpose. This does NOT have to be complicated, but we certainly can make it so.

Just my tiny 2 cents...

Joel DuBay Sr

Bigsmith

03-06-06, 03:26 PM

bpape

03-06-06, 03:51 PM

Wasn't trying to ask questions - just cautioning that what Bob said was true for treatment coverings it isn't conclusive enough necessarily for going in front of speakers.

Now putting it in front of a reflection point absorber that's supposed to absorb highs anyway is just fine. That's what's pretty much always been said here - if you can breathe through it easily, it's OK to put in front of treatments. I don't know that anyone's ever said it was a conclusive test for in front of speakers.

Even some cloth that is relatively easy to breathe through (some of the non FR701 GOM for example) can have some pretty serious attenuation in the high frequencies - hence not acceptable for in front of a speaker.

Don_Kellogg

03-06-06, 04:20 PM

The theater is 28' in length 12.5 feet wide and probably a 7.5 average height. Room has been framed out of 2x4's, insulated with R13 thermal acoustical insolation. All walls covered with 2 layers of 5/8" drywall, ceiling has a single layer. I didn't know about Green Glue at the time so the second layer of drywall is held up by drywall adhesive some screws. Floor made of cement, covered with thick padding and carpet. There are 3 doors in the room and there is an arch that opens to the stairwell to upstairs (Door up top). Also one egress window which I have covered with thick curtains and set foam in.

I'm in the process of trying to hack this together while I save to enlist Dennis to do a projob. The room seems to have some what of a flat response according to my Pioneer amp MCACC or what ever it is called :) Currently I have the 2" aurlex foam covering the undersides of the soffits, which are 4' (Do to air ducts). The bass traps are in each corner and cover from carpet to soffit. I used the mirror trick to figure out where the side wall reflects are. Other than that there is no treatment.

Two limiting factors for me are width and height, unfortunately we had only 8' ceilings in the basement. I would hack up the floor and lower it but I'm not sure that is a good idea as it would be lower than the footers.

myfipie

03-06-06, 06:49 PM

Don,

> I have 12 large wedge bass traps from Aulex, I plan to use them in the corners to help with Bass. Is this too much <

Too much? It's probably not enough. :D

--Ethan

I think I would disagree with Ethan on this point ( :D ;) ).. One problem with foam bass traps is not only do they absorb bass (a little) but absorb way more of the high end.. I really think you should look into putting a few bass traps with a membrane system in them.. This will help tame the low end and let the 2 inch foam work on the high end.. It is all about balance in a room.

Glenn

BasementBob

03-06-06, 06:59 PM

myfipie:
Actually, Auralex MegaLENRDs are pretty good broadband absorbers, right down into bass.

Don_Kellogg

03-06-06, 09:07 PM

I just wondered I have a bunch of money tied up into these would be nice to use them :)

Stima

03-06-06, 09:13 PM

I'm in the process of trying to hack this together while I save to enlist Dennis to do a projob.

Don,

If you are going to spend the money to fly Dennis from Atlanta to Michigan, may I suggest you STOP NOW and not spend another dime!! I can't see the sense in building your room completely wrong and THEN flying the expert in. You will spend thousands for him to tell you the theater was built completely wrong and would have to be torn down to get it to his standards.

Just a thought....but I am simply paraphrasing what Dennis told me when I did the same thing. (I have the luxury of living in the same town as he, so I saved on the airfare.). If Dennis is brutally honest, you are not going to like what you hear...I didn't. :(

Joel DuBay

03-06-06, 09:27 PM

I think I would disagree with Ethan on this point ( :D ;) ).. One problem with foam bass traps is not only do they absorb bass (a little) but absorb way more of the high end.. I really think you should look into putting a few bass traps with a membrane system in them.. This will help tame the low end and let the 2 inch foam work on the high end.. It is all about balance in a room.

Glenn

Interesting. I did not know you were a proponent of membrane systems Glenn. I thought you were of a different opinion. So, do you think that (in general for Home Theaters specifically) corner absorption should not include HF as well as Bass Absorption?

By the way, I don't think that opinion is good or bad, wrong or right....I just think it is interesting and that this discussion is very informative. We certainly never tire of learning.

I am interested to hear your opinion.
(I have an email into you Glenn)

Joel R DuBay Sr

bpape

03-06-06, 09:32 PM

Joel DuBay

03-06-06, 09:37 PM

I think Glenn's point is well taken. It might be possible to overdo the high frequency absorbtion. That said, Ethan generally is a proponent of FSK faced absorbtion so that would not be nearly as big an issue - and does in fact act as a damped membrane. His MiniTraps are also of a membrane type design.

That sounds like and endorsement Bryan. And, I do not think that is neccessarily wrong. Are you a proponent as well?

Cheers for a good discussion.

Joel R DuBay Sr

myfipie

03-07-06, 08:37 AM

myfipie:
Actually, Auralex MegaLENRDs are pretty good broadband absorbers, right down into bass.

I don't think I said they where bad (if I did then sorry) but not the best thing for bass trapping..

myfipie

03-07-06, 08:46 AM

I think Glenn's point is well taken. It might be possible to overdo the high frequency absorbtion. That said, Ethan generally is a proponent of FSK faced absorbtion so that would not be nearly as big an issue - and does in fact act as a damped membrane. His MiniTraps are also of a membrane type design.

Actually I was talking about a damped membrane.. Wood panels are great, but not for smaller rooms.. Sorry if I miss typed, I think I still have ski brain from last week. :D

Glenn

bpape

03-07-06, 11:32 AM

Joel.

I'm a proponent of the right mix of materials for a given room. Almost always, some will be faced (damped membrane) and some will be unfaced. I've found it very rare where the room 'falls into place' with all unfaced materials without overdamping the highs.

Glenn,

Gotta get those ski-bunnies out of your dreams ;)

Scott R. Foster

03-07-06, 11:52 AM

myfipie:
Actually, Auralex MegaLENRDs are pretty good broadband absorbers, right down into bass.

True that - A true broadband device. Easiest thing in the world to install also.

1) Open box

2) Stack units

3) Open 2nd beer - aaaahhhhh!

Pricey though, at about $75 per linear foot of treatment last time I checked.

That kind of number adds up quick. You could easily spend an additional $2000 on your room's corner treatments alone versus use of one of the available panel type mineral fiber based products - and all that for only modest gains in Sabin content.

If you are even thinking about a DIY solution the cost of ML's is a strong incentive.

myfipie

03-07-06, 12:24 PM

"Gotta get those ski-bunnies out of your dreams "

I must say that Whistler Mountain outside of Vancouver offers some really nice bunnies!!! To bad they can spot a poor person a million miles away.. :)

Glenn

Terry Montlick

03-07-06, 01:46 PM

Agreed Dave.

The "breathe" test is a standard, albeit non-scientific way of determining if a material is NOT breathable, more so than to determine if it is "breathable". Many fabrics are NOT breathable/ transparent in the acoustical sense. Thick canvas is NOT breathable in the acoustical sense, but, it doesn't (for instance) impede the ability to affect low feequency sound waves when used as a bass trap (only) cover. For speaker covers however, a material must not just be "breathable", it must be VERY easy to breath through. Thin nylon (such as stocking material) is a very breathable fabric, especially when stretched. Grill cloth is "breathable". And as such, this is the standard by which other materials are gernerally judged. In a non-scientific world, I believe as you do, that the more a fabric acts (when breathed through), like speaker cloth, the more likely it is going to work for said purpose. This does NOT have to be complicated, but we certainly can make it so.

Just my tiny 2 cents...

Joel DuBay Sr
I agree about the "blow-through" test. It is a quick and dirty way to get some idea of acoustic resistance, as specified precisely in ASTM C522-87, "Standard Test Method for Airflow Resistance of Acoustical Materials." As such, it tells you something about the "DC" resistance -- not as good as the frequency-dependent resistance, but pretty useful.

It is kind of like the acoustician's "hand clap" test to judge the general acoustics of a space. It is also quick and dirty, but gives you some very useful information. Last year there was a visit to a local cavern as part of an Acoustical Society of America function. Leo Beranek, one of the deities of modern acoustics and founder of many of its principles, was along (and going strong after more than 90 years on the planet). The first thing he did in the cavern was clap his hands and listen!

Regards,
Terry

Joel DuBay

03-07-06, 10:18 PM

Right on Terry... :cool: :)

That's quite a signature ya got there!! :eek:

Joel R DuBay Sr

Scott R. Foster

03-08-06, 11:23 AM

Pfft.. forget about the siggy, check out the web site.

http://www.tmlaboratories.com/

Nice pics. :)

I especially like use of "The Scream" under the title "Symptoms of Inadequate Home Theater Acoustics":

http://www.tmlaboratories.com/images/munch.scream.jpg

classy AND funny.. you don't see that every day.

Terry Montlick

03-08-06, 11:34 AM

Don_Kellogg

03-10-06, 09:33 PM

True that - A true broadband device. Easiest thing in the world to install also.

1) Open box

2) Stack units

3) Open 2nd beer - aaaahhhhh!

Pricey though, at about $75 per linear foot of treatment last time I checked.

That kind of number adds up quick. You could easily spend an additional $2000 on your room's corner treatments alone versus use of one of the available panel type mineral fiber based products - and all that for only modest gains in Sabin content.

If you are even thinking about a DIY solution the cost of ML's is a strong incentive.

Yeah you correct the price was a little steep, I bought 12 of the bass traps, and 48 of the 2 x 4' panels for the walls and soffits. Oh well what can you do I do got to admit it did make the room sound allot better.

Scott R. Foster

03-11-06, 01:47 PM

I do got to admit it did make the room sound allot better.

I bet they did.. Auralex makes good stuff. Their top of the line is highly effective and easy to use... good looking too IMO.

Don_Kellogg

03-12-06, 08:30 PM

I saw some of the Auralex ceiling panels in the transporter room on Star Trek The Next Generation. Looks like this stuff has multiple purposes....

I just worrie that maybe this is not as good as the insulation treatments most people are putting behind fabric on the forums. But it did make the room sound better I don't have the ping effect when I clap...

bpape

03-13-06, 07:58 AM

The Auralex stuff is perfectly fine for general mid/high decay control and reflection point control. The bass treatments are IMO not as effective. Comparing apples to apples, put 4" of Auralex foam across a corner and compare it to 4" of 703, 705, or mineral wool and the 4" of foam will finish last every time.

The Auralex bass treatments are solid. To compare fiberglass/mineral wool/cotton to them, you'd need to replicate the same solid absorbers of the same dimensions.

Don't get me wrong - if you want something easy to put up and don't mind the look (some like it - some don't) it's certainly an easy - though much more expensive solution.

BasementBob

03-13-06, 11:57 AM

bpape:
Comparing apples to apples, put 4" of Auralex foam across a corner and compare it to 4" of 703, 705, or mineral wool and the 4" of foam will finish last every time.That seems an unexpected statement.
I wasn't aware that Auralex made uniformly 4" thick foam panels. They make a variety of contoured (e.g. wedge) and 2" designer-fabric looking beveled-edge stuff. Which Auralex product are you thinking of?

srthomas21

03-13-06, 03:55 PM

Now I'm confused as hell. My plan was to insulate, drywall and paint. My room is 17 ft wide by 30 ft deep with 8 ft cielings and soffits on both sides of the cieling.

I really don't have the technical skills to figure all this acoustical treatement stuff out so if I dont' do anything is the room going to sound like crap?

It seems like there are a lot of experts that post on this thread so what advice would you recommend for a complete newbie to at least add some acoustical treatement to my room?

From what I've read it seams I should add some type of soundboard to the entire front wall as well as the sides of the room up to ear level.

I really don't want to mess with fabrics and such so if put the soundboard up on the wall and then put drywall over it and paint it would that work or would the drywall defeat the purpose of the soundboard?

Anybody dare to make a summary of the 34 pages of this post geared toward newbies just wanting to add some acoustical treatment to their room without getting technical if that's even possible? Most of the posts on this thread are way way over my head :)

I found this stuff but I don't know if its any good:

http://www.4seating.com/accessories/Accessories-WallPanels.htm

Thanks

Scott

bpape

03-13-06, 04:08 PM

Agreed Bob. I'm just trying to compare apples and apples. At it's thickest point, the Auralex is 2" or 3" or 4" or whatever. You can put 2 pcs of 3" face to face and get solid 4". Just trying to make a fair comparison. 4" of 705 of the same surface area of the LENRD (solid) doesn't seem quite right since thickness plays a part in the equation - not to mention that the LENRD is STILL more expensive.

Scott,

Yes - you're defeating the purpose by putting drywall in front of it. Insulation IN the wall helps with isolation. Absorbtion inside the room is what helps with the in room acoustics.

Stima

03-13-06, 05:02 PM

... if I don't' do anything is the room going to sound like crap?

Well, since "crap" isn't defined in acoustical terms, it's hard to get you a yes\no reply. However, I would say if you're going to spend all the money on a home theater room, you will be disappointed in it's performance if you completely skip sound treatments.

...would the drywall defeat the purpose of the soundboard?
Yes and no. Putting drywall over the acoustical panels make them useless for mid\high frequency absorption but they will act as very poor base traps. For what you are looking for, however, DO NOT put the panels behind the drywall.

Anybody dare to make a summary of the 34 pages of this post geared toward newbies just wanting to add some acoustical treatment to their room without getting technical if that's even possible?

Basic design:

Mid\High Frequency Absorption:

Use 1" 3lb (density) rigid fiberglass material (Owens Corning, Johns Mansville, others) on entire front wall (floor to ceiling) and on side walls up to ear height. The ear height number is more a rough AREA and less to do with placement. You can put the panels in the middle of the wall if you desire. You also need to treat several points on the side walls from floor to ceiling. These points are called First Reflection points. It takes two people to find these points. First, place a light at each front speaker location, then have on person move a mirror on the side wall as you sit in the each seat. Watch for the light to appear in the mirror. This is a reflection point and NEEDS to be treated. Repeat for each speaker and each seat. You can also do this for the ceiling if you are feeling adventurous.

Mid\High Frequency Diffusion:

Since you have a very long room, it would be good to put some diffusion on your rear wall. This can be as simple as book shelves, or as exotic as retail foam diffusion panels found online. Smaller rooms don't need this, but at 30', you should consider it.

Low Frequency Absorption:

Bass traps are a good thing. Typical placement is in each corner either straddling or filling the corner. Typical material is 4" (3 or 5lb density) rigid fiberglass...again Ownes Corning, Johns Mansville, ect. Typically these run from floor to ceiling and are 24" across. These panels can also be placed across ceiling to wall or floor to wall corners.

I hope all this helps. If you REALLY don't want to mess with all this stuff, I would suggest you have a pro come out and install the correct panels in the correct spots for you. They can use premade panels and save you a load of trouble, albeit at a decent cost.