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Building a room...need some wall treatment ideas - Page 2  

post #31 of 275
Jay,

> For the traps in the corners <

For best results they should be mounted straddling the room corners at a 45 degree angle, or at least close to 45 degrees. Here's a simple drawing from my Acoustics FAQ:

http://www.ethanwiner.com/corner-trap.gif

> I have seen some rooms have a border made of carpet (like trim board). Does this act as the bass trap? <

No, carpet on a wall absorbs only high frequencies. A good explanation of absorber panels, frequency ranges, and other related issues are in my Acoustics FAQ linked immediately above.

--Ethan
post #32 of 275
Steve,

> I would stuff the joist cavities with R19, attach a fire resistant fabric to the joists, then cover with some sort of molding? <

I'd pack the space with the thickest fiberglass that will fit. My partner recently treated his home recording studio ceiling this way, and he used fiberglass 12 inches thick. (I think that's the R30?) Other than that, what you describe is just right. The beauty of this is it's not difficult to staple fabric to the bottoms of the joists, and it's very easy to apply trim strips to hide the seams.

The Ceiling Max kit Mark linked to also looks good, but I wouldn't use that instead of thick fiberglass between the joists. Rather, I'd consider that instead of the fabric and wood trim, in addition to the thick fiberglass.

--Ethan
post #33 of 275
Thread Starter 
Ethan

I read over most of that page...some good info...again more questions (sorry for any inconvenience this causes).

1. The corner bass traps...I assume this is just as valuable in a home theater as in a studio...is this correct?

2. The corner bass trap in the image is 24 in wide. Was this size just chosen due to the fact that the panels come in 24 in sections? Can a smaller one be used with similar results?

3. How long does the bass trap have to be? I was planning on using 4-5 ft panels everywhere else in the room...would that work for the bass traps also?

4. If I put the traps only in the back of the room (because the FE of the room will be full of equipment, will it through the accoustics off...make it uneven?

5. From reading that page, i am currently planning on using an absobing material on both my bass traps and wall panels...using an absober to do the work of a diffuser...is that correct? And a good idea?

6. On the side panels, if I want to still get a lively room and help low frequencies, i can alternate sides of the panel (paper and non-paper)...is this recommended? With the bass traps, would it best to keep it to just the paper side out?

I'm sure i'll think of more questions as soon as i send this...

thanks
jay
post #34 of 275
Thread Starter 
I called Owens corning, and they told me that you can't get the 700 series insulation without going through a commercial channel.

In general, all i can in the stores around me is the foam insulation. I have found it as dense as R10...but i don't know what the accoustic properties of these insulations are...
post #35 of 275
Jay,

> sorry for any inconvenience this causes <

Not at all. I'm glad to help.

> The corner bass traps...I assume this is just as valuable in a home theater as in a studio...is this correct? <

Yes, of course. The goals are exactly the same - to have a low frequency response that's as flat as possible, and to cure flabby and muddy sounding bass that obscures clarity and articulation of bass instruments.

> Was this size just chosen due to the fact that the panels come in 24 in sections? <

Yes.

> Can a smaller one be used with similar results? <

The narrower you make it, the less surface area you have absorbing. It will still work, but you'll need to cover more corner surface area to get equal results.

> How long does the bass trap have to be? <

The more surface area you cover, the better the results.

> If I put the traps only in the back of the room <

You're better off covering the rear corners too. And some of the ceiling corners. It all depends on how good results you want, versus how many panels you're willing to have to look at. :D

> using an absober to do the work of a diffuser...is that correct? <

No, those are opposite tyes of treatment.

> With the bass traps, would it best to keep it to just the paper side out? <

Yes, have the the paper facing into the room for corner mounted panels, and the fiberglass side facing the room for any you put on the walls and ceiling.

> I called Owens corning, and they told me that you can't get the 700 series insulation without going through a commercial channel. <

That's why my company started selling it - mainly as a service to the DIY community because it's so difficult to get.

--Ethan
post #36 of 275
Thread Starter 
this is my room layout for my next post....
LL
post #37 of 275
Thread Starter 
Ethan...

It sounds like i need to take two giant steps back. I attached a picture of the layout i have been working on in autocad (let me know if the picture quality does not come out).

I'll explain what it all is...the speakers and couch are probably self evident. I calculated the first order and "second order" (don't know if that is the correct name) reflections and marked them on the walls. The longer lines are the first order. I have both 2' wide and 3' wide panels on the walls as I am trying to decide which size i would use. I also put bass traps in the back corners (may add more later depending on how things go). I didn't add the door yet...it will probably be behind the couch on one of the side walls (replacing one of the panels).

So in my designing so far, i have assumed i would put these fiberglass panels in all the spots indicated (side walls and corners). If I am understanding things now, it might not be the best way to do it. Doing what i have here would help with bass consistency (with the traps) and then some of the echos/ringing with the panels. It would NOT help take care of the first order reflections. Is this correct? What would you recommend (besides lacing the entire room with traps =p) with a room with this set up?

As a side note, I included the elevation drawing of the room. it shows the constraint I have with the heating vent on the left portion of the ceiling.
post #38 of 275
Quote:
I'd pack the space with the thickest fiberglass that will fit. My partner recently treated his home recording studio ceiling this way, and he used fiberglass 12 inches thick. (I think that's the R30?) Other than that, what you describe is just right. The beauty of this is it's not difficult to staple fabric to the bottoms of the joists, and it's very easy to apply trim strips to hide the seams.
This is a fascinating idea to me, as I've got very low ceilings in my basement and have been trying to figure out how to cram a theater in down there. My big question is whether or not this technique is strictly "don't ask don't tell" as far as construction goes? That is, it strikes me as the kind of thing that would give an inspector a heart attack! Or is this a common/safe technique?
post #39 of 275
Jay,

I could have sworn I answered this yesterday! :rolleyes:

> Doing what i have here would help with bass consistency (with the traps) and then some of the echos/ringing with the panels. It would NOT help take care of the first order reflections. Is this correct? <

It's hard to tell from those small figures. For straight walls and a flat ceiling, the first reflection points are on the walls and ceiling halfway between you and the front of the loudspeaker.

--Ethan
post #40 of 275
Band,

> This is a fascinating idea to me <

What's so cool about a totally absorbent ceiling is that acoustically it's identical to a ceiling that's infinitely high. In either case, any sound that goes up never comes back. So it never gives a closed-in boxy sound.

> it strikes me as the kind of thing that would give an inspector a heart attack! <

I can't imagine why. Fiberglass is often put in ceilings, and it's certainly not flammable. Even fabric is not a risk because it has so little bulk, for lack of a better word. And if there's any question about fire safety, use either flame retardant fabric, or you can spray flame retardant on any other fabric.

--Ethan
post #41 of 275
Thread Starter 
I figured it the image wouldn't come out well. I will try to post a different one when I get back home tomorrow.

I think i was mainly trying to get a recommendation on what i should put where based on my current room design. The quick description shows a rectangular room (13.5'x18') The front speakers a couple feet from the front wall. I made an equilateral triangle between the speakers and the sitting location on the couch...

The bass traps in the back corners. On the side walls, three panels. I was planing on having all of them be the fiberglass. I had planned to put them where i had calculated the reflections to be. Now, I am thinking that i need to put something else where those reflections are...like a reflective panel angled into the room or a rounded surface. If so, where do i put the absorbing panels on the wall..any where else that i can fit them (in addition to the traps in the corners)?

Or is it enough that i have all those absorbing panels, that the first order reflections aren't too much of a concern....or, if I angle the absorbing panels into the room slightly...would that have a similar effect?

All in all...I know the ideal room should have absorbtion and diffusion...but figuring out what all to put where...that is where i am struggling
post #42 of 275
Hi Ethan,

Are there any pictures of this technique using fiberglass, stapled fabric and wood strips? I am starting construction and HT is just below main LR, so isolation is not really a big deal.

Just not sure about aesthetics when finished.
post #43 of 275
Thread Starter 
here is a better copy of the picture of the designs.....
LL
post #44 of 275
Jay,

> trying to get a recommendation on what i should put where based on my current room design. <

You need thick panels of rigid fiberglass in the room corners, plus more panels on the side walls and optionally the ceiling at the first reflection points. You can use thinner panels for the latter.

> Now, I am thinking that i need to put something else where those reflections are...like a reflective panel angled into the room or a rounded surface. <

No, use rigid fiberglass panels.

> figuring out what all to put where...that is where i am struggling <

I've probably posted this image before, but here it is again:

http://www.realtraps.com/placing_mt.gif

The side wall panels marked "3" will move to the reflection points. In fact, you may be able to get away with only two on the side walls in the front part of the room, and one or two more on the ceiling. I'm not so sure diffusion is useful in that size room, but I suppose you could try it.

--Ethan
post #45 of 275
Limo,

> Are there any pictures of this technique <

I don't have any though I've done it several times.

I guess I should have taken some photos. D'oh! http://www.ethanwiner.com/misc-content/homer.gif

But it's easy enough to explain. Get fiberglass that's as thick as your joists are high, and fill the entire space between all joists. Then get a large wide roll of fabric and attach it on to the bottoms of the joists from one end of the room to the other. You can apply it in either direction - cutting across the joists or in the same direction - depending on what looks better in your room. Note that if you go in the same direction you'll have to trim the fabric so it ends on a joist boundary. Once the entire ceiling is covered with fabric stapled in place, cover the seams between each section of fabric with wood trim strips.

--Ethan
post #46 of 275
Thread Starter 
This looks pretty close to what i had in mind...save the two bass traps in the front and the panels on the ceiling.....This is great....thanks

Now...I think i have most things answered...the last thing for me to figure out, is what to make my ceiling out of....this was somewhat talked about before.

I'm not sure if I should do the fully dead ceiling (insulation and cloth)....partially due to the fact that i plan on having carpet floors (might make the room too dead) and i have that vent to contend with (as you could see in the elevation drawing.

I might use drops and or box it in with drywall. Either should be doable from a construction standpoint, and it seems they would be about the same acoustically. Either way i might have to treat some of the ceiling surface (especially if my rear speakers end up close to the ceiling).

Not sure what to do yet...
post #47 of 275
Ethan, thanks for taking the time to share your expertise with us. I've been looking for 703 and 705 locally, but have yet to have any luck. Lowes can order it, but Owens Corning will only sell it in mass quantities. So, it looks like your site may be my only option. But, I have a couple questions before I order.

Considering the substantial price difference between the 703 and 705, it would seem much more affordable to to buy 703 and double or even triple up on them. Would this be less optimal to one sheet of denser 705?

Also, I have a small room 12.5' x 11' x 8' high. So, space is at a premium. To avoid protruding out of the corners so much, would two 1 foot widths (one panel split in half-doubled or tripled if using 703) placed in each of the 8 corners be equivalent to one 2' wide panel in each?

My current plans are to place bass/high-mid frequency traps in each of the corners as advised on your site, with additional 1" high/mid frequency traps at each of the first reflection points on the walls and cieling - spaced off the wall a bit. I also plan on building some additional, movable traps on stands, to be placed around my father when he watches with us, as he is very hard of hearing and the added absorption would probably help. I have 4 dipole surround speakers, so the top half of the room will remain alive, though I might make some diffusion panels to avoid standing waves. All walls and the ceiling will be draped in black burlap to conceil light reflections, the acoustic treatments, and some wiring.
post #48 of 275
anyone have a suggestion as to what type of fabric to wrap the panels in?
post #49 of 275
Thread Starter 
Quote:
Originally posted by marcbarton
anyone have a suggestion as to what type of fabric to wrap the panels in?
I believe the recommendation made, was anything that is non-reflective, porous, (i.e. not silk) and will allow air to pass through.
post #50 of 275
Hi all,

I'm currently looking at acoustic treatments and after seeing a really good application photo on their website (I posted a link on the Audio theory forum), I've put Auralex at the top of my short list. I just want to ask how effective are these fibreglass compared with 'proper' acoustic treatment like Auralex? Do the wedge shapes of the latter offer any benefits over the fibreglass? At the moment I'm swinging towards Auralex as it's seems like less hassle and I also think the charcoal grey wedge panels look good (if done right).

Thanks.
post #51 of 275
Chad,

> Considering the substantial price difference between the 703 and 705, it would seem much more affordable to to buy 703 and double or even triple up on them. Would this be less optimal to one sheet of denser 705? <

Yes, for a given thickness 705 is twice as dense and therefore about twice as "good" as 703. That's why it costs more per cubic measure than 703. So you'd need four inches of 703 to get as good low frequency absorption as two inches of 705.

> would two 1 foot widths (one panel split in half-doubled or tripled if using 703) placed in each of the 8 corners be equivalent to one 2' wide panel in each? <

Yes, you can use narrower panels, but you need to compensate by making them longer - covering more of the corners - rather than simply making them thicker.

> My current plans are to <

That all sounds just right.

--Ethan
post #52 of 275
Sarah,

> effective are these fibreglass compared with 'proper' acoustic treatment like Auralex? <

Fiberglass is much more effective than foam. For a given panel thickness 703 fiberglass is about twice as effective as acoustic foam, and 705 fiberglass is about four times more effective. Other techniques can improve the low frequency performance of fiberglass even further. So in truth, most acoustics pros consider fiberglass the basis of "proper treatment" and rank foam panels well behind.

> Do the wedge shapes of the latter offer any benefits over the fibreglass? <

Not really. The wedges increase high frequency absorption a little, but at the expense of lesser absorption at low frequencies. However, all rooms need absorption much more at low frequencies than at high frequencies.

--Ethan
post #53 of 275
Thanks again Ethan. That's what I meant, stacking one above the other, vertically.

:)
post #54 of 275
Quote:
Originally posted by Ethan Winer
For a given panel thickness 703 fiberglass is about twice as effective as acoustic foam, and 705 fiberglass is about four times more effective.
In general, I agree about the thickness of fiberglass vs. acoustic foam. You need roughly twice as much thickness of foam to equal the equivalent absorption of fiberglass.

However, fiberglass density has little affect on absorption. Twice the density for 705 is not twice as effective as 703. There is plenty of published data on fiberglass absorption. There can be a "steepening" of the middle of the S-shaped absorption curve for denser material. But this doesn't translate into more effective absorption.

Here is the absorption coefficient data which Owens Corning publishes for "type A" mounting of their 700 series unfaced fiberglass.

http://www.tmlaboratories.com/700absorption.jpg


Regards,
Terry
post #55 of 275
I should have also mentioned, for the sake of others who are not familiar with the Owens Corning 700 series, that 701 has a density of 1.5 pounds/cu. ft. 703, at 3 pounds/cu. ft., is twice the density of 701. 705, at 6 pounds/cu. ft., is twice the density of 703.
post #56 of 275
Terry, am I interpreting your chart correctly if I infer that below about 300 Hz 701 absorbs more sound than 703, and 703 is better than 705 ?

Thanks ... /FP
post #57 of 275
Quote:
Originally posted by Ford Prefect
Terry, am I interpreting your chart correctly if I infer that below about 300 Hz 701 absorbs more sound than 703, and 703 is better than 705 ?
Yes, that's what it shows, at least to a small extent. Again, I am simply plotting the data published by Owens Corning. It is from their Pub. No. 5-IN-14775-J, "Submittal Sheet - Fiberglass 700 Series Insulations." A link to the PDF file was given a while back on this forum.

One caveat - at lower frequencies, the margin of error of these measurements increases. However as I pointed out, this "steepening" of absorption curves for denser fiberglass (or corresponding "shallowing" for less dense fiberglass) has been generally observed.

- Terry
post #58 of 275
Terry,

> There is plenty of published data on fiberglass absorption. <

The problem with the published data is it ignores how rigid fiberglass is actually used to absorb low frequencies. Believe me, I've been around and around with a number of acousticians about this, and I remain convinced that density is a big factor in LF performance. Below are the points I made recently about this elsewhere.

--Ethan

Some people claim that low frequency performance of rigid fiberglass is not a function of its density, and use as evidence the data published by Owens-Corning that compares 701, 703, and 705. The density of these types of rigid fiberglass increase with their product numbers. That is, 705 is denser than 703, which in turn is denser than 701.

I have never performed lab tests using different densities, but there's a lot of evidence that increasing density does in fact increase low frequency absorption. For starters, the head acoustician at Owens-Corning (Dr. Godfrey) told me it does, and as proof he sent me a 20+ page technical article. Data faxed to me by Rock Wool Manufacturing in Leeds, Alabama also shows a direct correlation. Further, I believe making rigid fiberglass more dense also increases its absorption at low frequencies because it starts to behave as a membrane all by itself.

http://www.ethanwiner.com/oc-data.gif

The data often cited, above, is incomplete because it's given in octave bands that go no lower than 125 Hz. Since I have personally measured fiberglass mounted across a corner to have a peak absorption well below 125 Hz, it's clear that octave data down to only 125 Hz is inadequate.

The Owens-Corning data above is also riddled with inconsistencies when viewed in this light. If we consider rigid fiberglass as having linear absorption due solely to gasflow resistance, then this data makes no sense. For example, why is two inches of 705 eight times more absorbent at 125 Hz than one inch? And why is two inches of 701 only a little better at 125 Hz than one inch? This shows that more is going on than plain gasflow resistance. Further, to really understand the relationship between density and low frequency absorption, the material should be measured as it's actually used - with an air gap rather than flat on the floor. By resting on the floor, which is how the above data was measured, any potential diaphragm behavior will be damped.
post #59 of 275
Quote:
Originally posted by Ethan Winer

...
The problem with the published data is it ignores how rigid fiberglass is actually used to absorb low frequencies.
...
Further, to really understand the relationship between density and low frequency absorption, the material should be measured as it's actually used - with an air gap rather than flat on the floor.
Rigid fiberglass is used in a variety of ways. The most common acoustical treatment is as a wideband absorber in "type A" mounting - flat against a rigid surface. The data do not address other types of mounting.

Quote:

... the head acoustician at Owens-Corning (Dr. Godfrey) told me it does, and as proof he sent me a 20+ page technical article.
I'm not familiar with this article, and would love to see it. Can you give me the reference?

Regards,
Terry
post #60 of 275
Ethan,

If you think Owens Corning data on A-mounted fiberglass is flawed, here is data from another manufacturer - CertainTeed. I'm afraid you won't like this either. :)

This graph is for their ToughGard Duct Liner. Type 150 is 1.5 pcf density, type 200 is 2 pcf, and type 300 is 3 pcf.

http://www.componentacoustics.com/CertainTeed.jpg

This shows the same steepening of the absorption curve with higher density. The 3 pcf fiberglass exhibits less absorption at 125 and 250 Hz than the 1.5 pcf material.

Regards,
Terry
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