Leon:

I paid about 120 bucks for two entire batts of 703-type fiberboard, so that sounds like a very high price...?

Jeff,

Did you do the batting on the 'untreated' area or is it still plain drywall?

Once again, asking whether it matters or not to room acoustics to use a perforated screen or not -- is the decision solely based on whether there's a speaker behind the screen?

I've treated screen wall with 4" 703 mounted 4" off the wall.

Speakers are out in the room, NOT behind the screen.

Would a perforated screen (mounted approx 4" in front of the 703) improve overall sound quality? Seems like it should, as it eliminates a largely reflective surface over a large fraction of the front wall. On the other hand, seems like most frequencies can find themselves around the screen anyway.

ps -- if answer is "it depends": room is 18' by 15' by 12'; first reflections off the side walls are being handled by 2" RPG binary diffusor panels or 7" skylines (will decide by ear); rear wall ceiling and screen wall corners all have soffits with bass trapping.

Brucemck2:

If you have a perforated screen, then by definition a lot of sound goes through it virtually without change (well they attenuate high frequencies a bit). If it's not perferated I've always assumed that it reflects highs but lows go right through it, but I've never seen measurements so I can't define 'highs' and 'lows'.
With the exception of first reflections, it makes less (none?) difference where absorbtion goes, as opposed to the absorbtive surface area and thickness (Sabine formula).

If your "Speakers are out in the room, NOT behind the screen", then I wouldn't get a perferated screen. The problem with perferated screens is moire, which is an visual interference pattern between the hole spacing of the perferations and the projector grid pattern. The second problem with perferated screens is you loose 10% of your brightness.

In my case I want a big screen in a short room, so I can't put my center above or below my screen, so it has to be perferated, so all the speakers are going behind it, along with, probably, a bunch of absorbtion.

Terry,

> Bill is right on both points <

He usually is!

> inversion of the low frequency room modal response can be done with extremely simple EQ <

Yes, but that's not what I was talking about! :p

I said, "Just as important is the way they reduce ringing, and in a way that EQ cannot." I didn't say anything about LF response, just ringing. I've heard from you and Dennis and others I respect that EQ can indeed help to tame the lowest modal boosts, and I accept that. Personally I wouldn't add an EQ to my system, but I understand why others do. Especially those who for whatever reason don't want to install a lot of bass traps.

--Ethan

Jeff,

Your question seemed to have gotten lost among all the chit-chat over phase response and axial modes. :D

> Could this echo be caused by the soffit? <

Echoes are caused by large areas of reflective surface, wherever they may be located. If two reflective surfaces are opposite each other - ie: parallel walls, or a reflective floor and ceiling - then you get a special case known as flutter echo. Flutter echoes have a specific pitch whose frequency is related to the spacing between the surfaces. So it sounds more like a "boing" than like normal "hello .. hello" echoes.

--Ethan

bpape and Ethan,
First, I didn't want to add batting to the upper section because from all I've read, it isn't necessary and is only used if one wishes to add fabric to the upper half of the wall. We wanted to do some special paint treatments to the upper half.

As for the echo, it is only bad in a couple of spots. I'm pretty sure it is being caused by the soffit. I'm going to add some additional fiberglass to that area.

If I were to use a parametric Eq to correct low frequencies (in my case 90Hz for example) on a full-range speaker, does it introduce phase errors across the entire spectrum or only around the center frequencies I am correcting?

Andy K.

Chris,

I am not sure when you bought yours but the price has increased quite a bit since January of this year. How thick was your 703 and how big is a bat? I could have purchased the 1"X10'X4' boards for less than half the price of the 2" ductboard per piece.

it was 1-inch thick boards, 16 per batt. I paid like 130 for two batts, more than enough for the whole room.

marjen:

You can use anything found on this page:
http://www.bobgolds.com/AbsorptionCoefficients.htm
(fiberglass, rockwool, cotton, polyester, even open cell foam)

So if I understand the info on this page. I could actually just put R-11 or R19 unfaces batts on the front wall, cover it will GOM or something similar and it would have the same effect as using something like 703, JM or other rigid fiberglass?

Originally posted by marjen
So if I understand the info on this page. I could actually just put R-11 or R19 unfaces batts on the front wall, cover it will GOM or something similar and it would have the same effect as using something like 703, JM or other rigid fiberglass?

If you look at the absorption coefficients, you'll see that R11 has signifigantly more absorption at some frequencies than 703:

125 250 500 1000 2000 4000 NRC
703: 0.11 0.28 0.68 0.90 0.93 0.96 0.70
R11: 0.34 0.85 1.09 0.97 0.97 1.12 0.95

Now here's the part I'm not sure about, because I was thinking of using R11 as well. The vast majority of my front wall is taken up by the screen. The screen is reflective to certain frequencies (I'm guessing > 500 hz or so...). Since most of the insulation will be behind the screen, does the screen serve to "counter" the extra absorption of the R11. So in practice, perhaps I can use R11 behind the screen, and then save the $$ 703 panels for elsewhere in the room.

But I won't know w/o measuring, and I unfortunately don't have any measuring equipment yet (I'm an all Macintosh/Linux shop at home, still need to build my Windows HTPC and even then, I'd need to invest the mic and whatever else is needed to measure).

j.

Having the R11 behind the screen will give you the absorbtion from the lower mids down while the screen will reflect the highs.

You CAN use R11 everywhere IF that is what your room needs and if you have a way to hide it. It doesn't tend to be as easy to make 'visually friendly' as the 703 @ 1".

Andy,

> If I were to use a parametric Eq to correct low frequencies (in my case 90Hz for example) on a full-range speaker, does it introduce phase errors across the entire spectrum or only around the center frequencies I am correcting? <

A lot of people don't realize this but phase shift is totally benign. The only time phase shift has an impact on audio quality is when two versions of the same signal are combined and one of those has been shifted. So if you add an EQ to your system and measure some frequency response, what you measure is what you have and any accompanying phase change at any frequency is irrelevant. (Assuming the same phase shift is applied to all channels.)

--Ethan

Ethan:

I thought there were several types of phase shift (time delay > 1ms):
a) equal delay on all speakers, but may be out of sync with the video.
b) different delay between two (or more) speakers -- as you mentioned
c) different delay for different freqeuencies - caused by bad EQ electronics, or bad crossover electronics, or bad bass management electronics, or a bad filter.
d) different delay because some speakers are further away from the listener than others (always happens, think 'two' listeners)
e) multi-driver (single speaker) time delay because if you're head is higher than the speaker then likely the tweeter is closer to you than the woofer
f) subwoofer phase shift control knob (really useful for modally placed subs that are tied to the front left and right channels using high-low filter hardware in the subwoofer), or for a center placed subwoofer.

Okay back to tri corners for a moment please. I will have a trayed ceiling in my room so I will have soffit on all walls. Do I treat the corners in the facial area of the soffit as well, they are 11" high? Also is the treatment at 45 degrees on all 3 axies for any tri corner treatment?

When you deal with a tri-corner, you are dealing with the intersection of length width and height. Treat the soffit tri-corner as the real one. The other one (depending on how wide the soffit is) is generally pretty far away from the length dimension.

Originally posted by BasementBob
jasplat88:
If you get bored and find yourself with nothing to do, what happens with the subwoofer/mic at these locations:
- subwoofer at (6', 2'6.6", 1') and the microphone at (13'3.1"", 7', 3'8.9")
- subwoofer at (5'11.9, 1'11.9", 1') and the microphone at (12'4.7"", 7', 3'8.9")
( RPG Room Optimizer, 20hz to 80hz)

Ok Bob,

I finally got to it....and wow....pretty impressive. Now what? The sub is off my front stage at both those locations, and the mic height is about a foot higher than where a head will be (although the seating location is almost spot on----from my front row prime viewing seat).

-Jason

Originally posted by kromkamp
If I were to use a parametric Eq to correct low frequencies (in my case 90Hz for example) on a full-range speaker, does it introduce phase errors across the entire spectrum or only around the center frequencies I am correcting?

Andy K.

A phase change is introduced on both sides of the frequency you are correcting.

It may be argued that this is not a phase error, but a phase correction. If the result of parametric equalization is a flatter spectrum, then the "distorted" spectrum of the room before EQ can be regarded as having incorrect phase, which the equalizer corrects. The resulting signal phase after parametric EQ will be the same as if the offending room modes weren't present to begin with.

Thanks Terry and Ethan. So, can you tell me why EQ is considered a last resort then? I agree that it doesnt solve the 'ringing' and long decay of problem frequencies, but I've always always read that EQ causes phase distortions which lead to a 'smearing' of the sound.

Andy K.

Andy,

Acoustic correction should always be attempted first, if at all possible. The problem with EQ is that it can only improve a localized area. Very low frequency absorption will improve the entire room, so there will not be seating issues.

While bass traps will improve a room and are advisable, a room with serious low frequency problems cannot be completely corrected without Herculean measures -- devoting a very major portion of the space to bass trapping. While possible for a studio, this is generally not a practical alternative for a home theater due to space, aesthetic, and/or budgetary considerations.

EQ is the next step after acoustical correction. In many cases, though, it can fix a room which is simply too problematic for completely effective very low frequency acoustic treatment. Unfortunately, the latter is the rule rather than the exception. :(

Regards,
Terry

Bob,

> I thought there were several types of phase shift (time delay > 1ms) <

It's important to distinguish between straight delay and phase shift. If you add straight delay to some channels more than others, the phase shift will be different for different frequencies. So the arrival time differences create peaks and nulls in the air where the waves combine. Likewise for phase shift if it's not the same in all speakers. The key point is that the response errors occur only as a result of identical content arriving from two different sources and combining. Without the combining, the frequency response is not harmed. Any phase shift or delay that's common to all channels is benign.

> c) different delay for different freqeuencies - caused by bad EQ electronics, or bad crossover electronics, or bad bass management electronics, or a bad filter. <

Phase shift caused by "bad" electronics is not an issue because presumably the same shift will be applied to all channels. Not counting a subwoofer which is a different issue. To be clear, electronics adding phase shift is neither bad nor undesirable. It occurs all the time, especially in equalizers, and is a fundamental part of how EQ works. If you haven't seen it yet, HERE (http://www.ethanwiner.com/EQPhase.html) is a short article I wrote that explains the role of phase shift in EQ circuits.

> subwoofer phase shift control knob <

That's a little different. The phase shift knob on a subwoofer is used to better align the two different sources - the subwoofer and mains - around the crossover frequency so both signals arrive at your ears in phase to avoid peaks and nulls.

--Ethan

Andy,

> I've always always read that EQ causes phase distortions which lead to a 'smearing' of the sound. <

This is a huge problem. Misinformed magazine writers (and even some pro recording engineers) have repeated that so many times it's now accepted as fact. Nothing could be further from the truth. The whole notion of phase shift causing "smearing" is based on fantasy. Room echoes can "smear" imaging, but that's not related to phase shift. See the article I linked above about how phase shift is inherent in EQ, and why some people wrongly believe phase shift is an audible problem.

--Ethan

Hi-

How kid and pet friendly are these materials? Do you need to cover them? Do they pull apart if messed with? Is one better than the other?

I am concerned with the stuff you put on the walls (versus in the walls).

Thanks,

Jeff over in another new HT suggested I repost this here.

I'm hoping to start my HT early in January and am quite excited but know very little about acoustics, but no doubt after reading through and following this thread I hope to be up and running:)


Just wondering:

Would it be possible not the mud and finish the sheet rock especially as the CertainTeed UltraDuct Gold covers the walls??? I can certainly do the framing and sheet rock but would Never dare do the mud and tape work - lol

Thanks so much for your advice.

Cheers,

Geoffrey

You really should do the joints with tape and at least a rough mud job even if it is going to be covered. You wouldn't have to sand it though or worry too much, just seal up the joints.

Good luck.

Thanks bpape:

I'll certainly take your advise and thanks again.

Cheers,

Geoffrey

I recently bought some Owens Corning 2 inch 703 from a roofing wholeseller for about 50 cents a sq. ft. They carried OC shingles and were able to get all OC products.

Man around here they are charging over $1 a sq. ft for any rigid fiberglass. I have called about 30 places and only 2 carry it so far. Ordering online would be more expensive do to shipping. This stinks.

Sorry, it was over 1 per sq ft. I just thru it out there as an option for getting the stuff. If you can just have it thrown on a load that is already coming in, the shipping isn't much.

marjen:
Man around here they are charging over $1 a sq. ft for any rigid fiberglass.Some people have been successful bartering over the price, offering to pick it up, etc. For example, one guy in england bartered from $1.50 per square foot down to $0.30 a square foot.

Help:

I can not find INSUL-Shield but I have found Owens Corning SelectSound Black in blanket form for about $216.00 for a 48"X100' roll.

Can I get a couple of quick opinions on using this instead of the INSUL-Shield?

Thank you,

Dave

My room is 20 by 14 by 7.5 I'm going to try and find some of the material listed at the very beginning of this thread.

If I'm able to find THIS (http://www.owenscorning.com/around/sound/commercial_acoustics/BLACKAC1.PDF) in the rigid form would it look OK to leave it uncovered?

My system will be 7.1, 6 of the speakers will be floor standing towers.

I must admit that this is all very confusing (figuring out which method of treatment to use).

I intend to use the room approximately 90 percent of the time for home theater.

So this is what I plan on doing (correct/stop me if I'm wrong)

Cover the entire front wall with 1 inch and the other three walls to match the height of my speakers.

Cover the bottom of the soffit with 1 inch as well.

HH

I guess you could leave it uncovered - it seems to be designed for that.

The perimeter of the room should be done to ear level - not to the top of the speakers necessarily.

Don't forget to do the first reflection points.

Originally posted by bpape
I guess you could leave it uncovered - it seems to be designed for that.

The perimeter of the room should be done to ear level - not to the top of the speakers necessarily.

Don't forget to do the first reflection points.

I would like to cover with fabric but I don't have the skills to do it right and haven't found a GOOD tutorial on DIY with pictures.

I will do ear level.

Doesn't ear level on three walls take care of the First reflection points?

HH

Originally posted by HuskerHarley
My room is 20 by 14 by 7.5 I'm going to try and find some of the material listed at the very beginning of this thread. If I'm able to find THIS (http://www.owenscorning.com/around/sound/commercial_acoustics/BLACKAC1.PDF) in the rigid form would it look OK to leave it uncovered?

I intend to use the room approximately 90 percent of the time for home theater.

So this is what I plan on doing (correct/stop me if I'm wrong)

Cover the entire front wall with 1 inch and the other three walls to match the height of my speakers. Cover the bottom of the soffit with 1 inch as well.

I'm in the exact same situation. Today, I will have 60 of the 2 ft x 4 ft black acoustic panels delivered. I will be applying them to the front wall, primary reflection pionts, around the perimeter at and below ear level, and on the bottom of the soffit. I'm not sure if it looks acceptable without a fabric covering but I hope so. I'll let you know after I see it tonight.

Originally posted by Carlton Bale
I will have 60 of the 2 ft x 4 ft black acoustic panels delivered.

I'll let you know after I see it tonight.

How much do they cost?

Please post a picture if you can.

HH

The insulation up to ear level gets the majority. Don't forget the ceiling though.

Originally posted by bpape
The insulation up to ear level gets the majority. Don't forget the ceiling though.

Please tell me what I should do so I get it somewhat correct the first time.

HH

You'll be fine on the walls. Some do the ceiling, some don't. If you want to calculate where to put them (mirrors are a lot harder on the ceiling! ;) ), draw it out. If you measure from the mid/tweeter center to the ceiling and then draw a phantom ABOVE the ceiling the same distance, then draw a line from that point to your ears, you have the hypotenuse (sp?) of a triangle. The other sides of it are the straightline distance from the real speaker to your ears and double the distance from mid/tweet to the ceiling.

Once you get that triangle trigged out, then you know the angles. From there, calc the triangle (phantom) above the ceiling and use the base for the distance from the speaker front out toward you. From side to side, put it in a straight line between you and the speaker.

This seems like a lot of math to some but to me it's easier than trying to get someone else to hold a mirror of decent enough size that I can actually see anything flat on a ceiling and move it around without being in the way.

Originally posted by bpape
You'll be fine on the walls. Some do the ceiling, some don't. If you want to calculate where to put them (mirrors are a lot harder on the ceiling! ;) ), draw it out. If you measure from the mid/tweeter center to the ceiling and then draw a phantom ABOVE the ceiling the same distance, then draw a line from that point to your ears, you have the hypotenuse (sp?) of a triangle. The other sides of it are the straightline distance from the real speaker to your ears and double the distance from mid/tweet to the ceiling.

Once you get that triangle trigged out, then you know the angles. From there, calc the triangle (phantom) above the ceiling and use the base for the distance from the speaker front out toward you. From side to side, put it in a straight line between you and the speaker.

This seems like a lot of math to some but to me it's easier than trying to get someone else to hold a mirror of decent enough size that I can actually see anything flat on a ceiling and move it around without being in the way.

I grew up in the crayon age and I'm embarrassed to say but I don't understand most of what you instructed me to do.

HH

Then get a stepladder, a decent sized mirror, a good patient friend, and some beer (not till after the mirrors are down ;) ) and find them that way.

It's tough to describe a math problem for 2 - 2 dimensional triangles in a 3 dimensional space with just text.

Originally posted by HuskerHarley
How much do they cost?

Please post a picture if you can.

HH

Agreed, curious about looks (uncovered) and cost. Thanks!

Couple of questions in the early planning stages of my theater.

What do you think of pre-made acoustic panels like these (http://www.acousticsfirst.com/frstresp.htm)? Are they good performance-wise? My company can get them as a dealer, and I like the way a darker color GOM covered panel looks on a black lower wall. If I got some 4'x4' or 4'x longer, and did them across the bottom, would an inch or more of space in between each panel for aesthetics hurt performance much? I think butting them right up to each other might look strange, but spaced slightly apart, they kind of look like art. How about some idea on cost for the "right" way to do it, with GOM fabric stretched over the JM duct liner stuff? Any idea about how much it costs to do it that way for a room 14'x 18' to 4' high? I would prefer to just do a moulding at the top & paint above instead of fabric all the way up if I use the fabric method. I will be having a GC build the room. So I would need to factor cost of materials and understand if an average competent GC can install this stuff & how long it might take. The pre-made panels are in the range of $280 for 4' x 10' so that gives me an idea to compare against. Let's leave the front wall out of the equation for now as I will need to treat it either way. And that brings me to my next issue:

I will be moving a very nice family room projection system into a new dedicated room. More info & pics of current setup here (http://www.avsforum.com/avs-vb/showthread.php?s=&threadid=488728&highlight=rear+projection) Note I have not updated that thread yet, but I am now thinking of abandoning the dual front/ rear two sided projection. I will update that thread as to why. Still not 100% sure.

Regardless, I LOVE my rear projection image and deep blacks I get from the screen, and think I now want to use that in my new dedicated theater if I can swing it. The question is how will it impact the acoustics (I'm guessing not well) and what if anything can I do to help? The screen is 80"x45" and it is 1/2" thick optical rear projection glass (not plexi.) It will go into a wall that is probably about 14' wide. It will have a rear projection room behind it. Glass screen framed into that separator wall like a window. I can treat that wall (and the back side too, if necessary) with whatever will help. But of course, unlike most of you, I cannot treat the area behind the screen, as the screen is glass.

Other info: the room will probably be about 17' to 18' deep. I have two full range tower L/R speakers w/ 12" sub/10" passive radiator for mains. One additional 15" stand alone sub. Thinking two rows of 3-4 seats each, back row on small riser. Probably a modified stage with three decoupled sections, sides filled w/ sand & middle w/ insulation (this is not on ground level.) Ceiling height to be 8' range, with two small areas about 17" lower. Screen (if I go RP, or keep my original dual FP theater/ RP family room idea) will be on the lower side, about 29" AFF due to where the RP screen is now. Actually, if I build the RP room over I can make that higher if needed. So I could put the center above or below.

Any info or tips on these issues for planning my acoustics most appreciated. Also, are there any good room planning software programs out there that are free or close to it, so I can play around with ideal room dimensions and seat/speaker placement while in the planning stages?

I've seen those from Acoustics First before. Unfortunately, they do not list individual absorbtion numbers at different frequencies. They also specify that they use 'high density fiberglass'. Generally, something around 3pcf is desirable. Higher densities can have issues with being too reflective at higher frequencies. Without knowing the specs, it would be almost impossible to determine what they will do in your application.

I received my Owens Corning SelectSound Black 2 ft x 4 ft panels yesterday; pictures are below. This is probably the best looking non-covered fiberglass panel there is, but I still don't think it is quite nice enough to hang on the wall uncovered, due mostly to the edges showing but also because the front isn't completely smooth and uniform. The front isn't too bad, but it's not as nice in appearance as a fabric covering would be. I'll probably cover mine with black grill cloth.

Front:http://www.carltonbale.com/hosted_images/OC_Acoustic_Black_front.jpg Back:http://www.carltonbale.com/hosted_images/OC_Acoustic_Black_back.jpg

Side:http://www.carltonbale.com/hosted_images/OC_Acoustic_Black_side.jpg

can anyone help with this scenerio?
I'm using the Danzian Celtic Cloth for an accoustically transparent screen (54"x96") with three in-walls for the LCR duties. The room is sorta large @ 24x24x8 and right now, the in-walls are pretty close with maybe a 1/4" gap between the screen fabric & front speaker baffle. Should i be concerned with treating the whole front wall or the area just behind the screen with a deadening material? Should i "float" the screen out and away from the speakers more than they are now even if i do/don't treat the area behind the screen?

rudee

Rudee,

> The room is sorta large @ 24x24x8 ... Should i be concerned with treating the whole front wall <

With dimensions like those you should by much more concerned about treating the lower frequencies. That room has a huge resonance at 71 Hz, and nearly as huge resonances at 24 and 47 Hz. All multiples of those frequencies are also resonating. The result is that all music will be very boomy sounding at those frequencies.

--Ethan

Ethan, I have a couple of questions about your previous post to Rudee. Please forgive me if these questions sound like I'm a novice. I am.

First, does it matter that Rudee's room has a huge resonance specifically at 71 Hz, and also at 24 and 47 Hz, as compared to having resonances at some other frequency? Let me explain where I'm coming from with this question... I have done quite a bit of reading on your web site at realtraps.com about bass traps. (By the way, the educational information and videos you provide are amazing!) Based on my understanding of your video on "Non-modal peaks and nulls in small rooms", it really doesn't matter what the resonances are related to a room's dimensions. Your video seems to prove to me that all rooms need broadband bass trapping and not trapping at specific frequencies. So would Rudee's room be treated any differently than a room that had equally huge resonances at some other frequency?

My second question is this, Would you treat a room differently if it has "huge" resonances at some particular frequency (like Rudee's), vs. a room that has more moderate resonances? Again, let me explain where I'm coming from with this question... Your educational materials indicated to me that you believe most rooms need 8 to 10 broadband base traps placed in corners. Is this true regardless of the bass problems that a room has, or is this an average? Would a room like Rudee's need more panels, or would the recommended 8 - 10 be sufficient?

Finally, I know the broadband bass traps ideally should go in the corners. However, if I place 8 - 10 traps in my room, does it matter if they are equally disbursed? For example, if due to aesthetics or practicality, I can not put a trap in one particular corner, Can I double-up in another corner to compensate? (By "double-up", I mean stack the traps so they cover the entire 8 foot tall area in the corner.) Or even more drastically, could I put all eight in the corners behind the proscenium and get satisfactory results?

wow - i hope all the questions above get answered b/c inquiring minds want to know! I have often thought what dreadful things were happening in here due to the square vs rectangle dimensions so often mentioned . The room doesn't sound half bad as is...
I am running a two tempest i/b located dead center between the mains in the front of the room and about 24" into the room and since it's an ib it's not going anywhere. Here's the very first frequency response i ran a few weeks ago.
Numbers below:
HZ r/s meter adjusted
17.5 80 87.3
20 88 94.2
22 88 93.4
25 88 84.4
28 80 79.6
32 72 75
36 80 82.5
40 80 82
45 92 93.7
50 102 103.3
56 102 103
63 104 104.8
71 106 106.7
80 102 102.5
89 106 106.4
100 112 112.3
112 91 91.25
126 95 95.2

sorry i don't know how to insert the graph but the numbers show a good dip from 25 to 45. These are the first numbers i have ever taken in this room and will be doing more testing as time permits. I'm thinking of doing a built in trap in each front corner as seen in some of the links on bobgolds site with oc 703 or equal. I didn't think the raw room numbers were too bad- i do have a bfd to help in the end but i wanted to address the room to some extent.
ethan, to the trained eye are my numbers relfecting the bad things you say are happening to the lower frequencies in this size space?


rudee

Originally posted by mikemav
clip...

I will be moving a very nice family room projection system into a new dedicated room. More info & pics of current setup here (http://www.avsforum.com/avs-vb/showthread.php?s=&threadid=488728&highlight=rear+projection) Note I have not updated that thread yet, but I am now thinking of abandoning the dual front/ rear two sided projection. I will update that thread as to why. Still not 100% sure.

Regardless, I LOVE my rear projection image and deep blacks I get from the screen, and think I now want to use that in my new dedicated theater if I can swing it. The question is how will it impact the acoustics (I'm guessing not well) and what if anything can I do to help? The screen is 80"x45" and it is 1/2" thick optical rear projection glass (not plexi.) It will go into a wall that is probably about 14' wide. It will have a rear projection room behind it. Glass screen framed into that separator wall like a window. I can treat that wall (and the back side too, if necessary) with whatever will help. But of course, unlike most of you, I cannot treat the area behind the screen, as the screen is glass.

Other info: the room will probably be about 17' to 18' deep. I have two full range tower L/R speakers w/ 12" sub/10" passive radiator for mains. One additional 15" stand alone sub. Thinking two rows of 3-4 seats each, back row on small riser. Probably a modified stage with three decoupled sections, sides filled w/ sand & middle w/ insulation (this is not on ground level.) Ceiling height to be 8' range, with two small areas about 17" lower. Screen (if I go RP, or keep my original dual FP theater/ RP family room idea) will be on the lower side, about 29" AFF due to where the RP screen is now. Actually, if I build the RP room over I can make that higher if needed. So I could put the center above or below.

Any info or tips on these issues for planning my acoustics most appreciated. Also, are there any good room planning software programs out there that are free or close to it, so I can play around with ideal room dimensions and seat/speaker placement while in the planning stages?

Sorry to bump, but I could really use some advice. Does anyone have any thoughts on how badly the glass RP screen will impact acoustics, or ideas to help? I need to make a decision later this week on which direction to go:
keep the RP screen for the family room & drop down a custom motorized front screen in front of it for the new theater room side (original idea in my post.) That screen would be custom built much like a blackout shade, and rise/lower in side channels to block light from coming from behind.
Or I may move the RP screen into the theater and bag the dual room idea, if I can find enough room for an RP booth and seating area in the new space.
Option three is to just go front projection in the new room like most people do, and that would make for best acoutsics, but that would mean wasting the $700 RP screen and custom integration I have now (and paying extra to have it removed.)
So the real question is, will an RP screen w/ a front screen directly in front if it be horrible for the sound or is there some way to deal with it? What do you think?

Scott,

> does it matter that Rudee's room has a huge resonance specifically at 71 Hz, and also at 24 and 47 Hz, as compared to having resonances at some other frequency? <

Yes and No. Yes, because good bass traps can succesfully target problems at 71 Hz and even at 47 Hz, but No because all frequencies need to be treated anyway. I pointed out the large resonance due to overlapping modes mainly to explain that even more bass trapping than usual is needed to make that room acceptable.

> Based on my understanding of your video on "Non-modal peaks and nulls in small rooms", it really doesn't matter what the resonances are related to a room's dimensions. <

Yes, to a point. But when two or three dimensions are the same or related, the modal resonances are even more pronounced than usual. So you need more bass traps to make the room acceptable.

> So would Rudee's room be treated any differently than a room that had equally huge resonances at some other frequency? <

Again, the main difference is that more bass traps than usual are needed.

> Would you treat a room differently if it has "huge" resonances at some particular frequency (like Rudee's), vs. a room that has more moderate resonances? <

Again, only as far as how many traps are needed.

> if I place 8 - 10 traps in my room, does it matter if they are equally disbursed? <

Not in the same sense as symmetry matters with speaker placement and listening position. The goals with bass trapping are 1) have enough of them, 2) put them across or at least near the corners, and 3) spread them evenly around the room as best you can. Exact symmetry is less important.

> if due to aesthetics or practicality, I can not put a trap in one particular corner, Can I double-up in another corner to compensate? <

You'd be better off adding a trap to a new place, like a ceiling corner.

--Ethan

Rudee,

> to the trained eye are my numbers relfecting the bad things you say are happening to the lower frequencies in this size space? <

The problem with those numbers is they show only part of the problem. You need to measure to at least 1 Hz resolution to really see what's going on. This graph, which I've posted here many times before, shows the response in a typical smallish room when measured at 1 Hz resolution:

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

Note the peak/dip pair at 110 and 122 Hz where the response varies a staggering 32 dB across a range smaller than one musical whole step. This activity is completely hidden if you measure at only 1/3 or 1/6 octave.

--Ethan

Mike,

> how badly the glass RP screen will impact acoustics <

Unless your speakers are pointing directly at the glass it's probably not a problem. Otherwise it's just one more reflective surface out of many others in the room.

--Ethan

Originally posted by Ethan Winer
Mike,

> how badly the glass RP screen will impact acoustics <

Unless your speakers are pointing directly at the glass it's probably not a problem. Otherwise it's just one more reflective surface out of many others in the room.

--Ethan

Thanks. The speakers will be forward of the screen and L/R off to the side a foot or two as well. I can treat the drywall surrounding the screen as well to try to help. Have not figured out the center yet- it will probably go above the screen tilted down slightly, or be just under the screen on a stand. Since the bottom of the screen will be only about 30" AFF high from the front row, I was thinking above may be better, but I would be glad for input here. It would be easier to mount it on a stand below & in front of the screen on the stage for sure. If I go above, I will have to build something out from the screen wall to hold it. Aesthetically, I was thinking it might look nice to have a center speaker bump out above the screen to hide the speaker, to mirror the curve of the stage below.
BTW Ethan- I was looking on your site, but the prices page takes me to the European site, which does not list prices. I am in the USA, so I think that is an error. Can you send me a link to get an idea about the cost of your traps?

Unless your speakers are pointing directly at the glass it's probably not a problem. Otherwise it's just one more reflective surface out of many others in the room.

I disagree. I've not played around with RPTVs which are smaller, but I will be including some movable thick curtains or panels for when I'm listening to music because my screen (FP, non-acoustically transparent) definitely damages the imaging and flattens the depth front/back.

ethan thanks so much for the further detail.
From the questions asked answered by you i can assume the following:
With the size of my room and the overall dimensions i have my work cut for me for getting this room treated to tame these ugly things- which is okay cause i'm at the point i'm ready to address the room.

I will go at it a bit blindly in the beginning and hopefully be able to devote more time to some of the room calc software as time permits.

-bass traps in corners- i can do both fronts and one rear fully and only a small top corner due to cabinets in the fourth corner. From what i gather i need heavy trapping- the denser the better?

-treat the whole front wall with a 1" oc 703 type material or linacoustic covered with a GOM or similiar material.

-treat the bottom half of the wall with a 1" oc 703 type material or linacoustic covered with a GOM or similiar material.

I could make a soffit trap using three sided wedges of compacted rigid fiberglass material wraped with GOM or simiar around the two side walls & rear if it would help do the trick in this room- Is there any chance this would be too much damping?

thanks much-
rudee

I have found a local place to purchase OC 703 or 705 & would like to see a detailed DIY Tutorial or guide that show's how to do EVERY step, especially how to cover with fabric.

I don't have the funds to hire some one to TEST my room for proper placement/location for the 703, so I will cover entire front wall and sides and rear to ear height.

Would it matter if I only covered from top of wall plates (electrical ect.) up to ear level (44"-48") for the sides & rear?

My room is 20'X14'5"X7'9" (LWH)

HH

& would like to see a detailed DIY Tutorial or guide that show's how to do EVERY step, especially how to cover with fabric.

I think once you get it you'll realize it's pretty easy to figure out. The two main ways that are used are a spray on glue and fabric right onto the fiberboard, or to make some kind of simple frame (or you can make it a spiffy elaborate frame if you so desire).

I just used a really cheapo frame idea, just a bunch of 1x4 boards nailed together, put the fiber board in there, and staple-gunned the fabric to it. I have no woodworking skills, so I went uber-simple. The only difficult thing was that home depot wood is total crap so the boards were warpy or would split, so I spent a few bucks for some little L brackets for a couple corners. Really easy.

Originally posted by ChrisWiggles
I think once you get it you'll realize it's pretty easy to figure out. The two main ways that are used are a spray on glue and fabric right onto the fiberboard, or to make some kind of simple frame (or you can make it a spiffy elaborate frame if you so desire).

I just used a really cheapo frame idea, just a bunch of 1x4 boards nailed together, put the fiber board in there, and staple-gunned the fabric to it. I have no woodworking skills, so I went uber-simple. The only difficult thing was that home depot wood is total crap so the boards were warpy or would split, so I spent a few bucks for some little L brackets for a couple corners. Really easy.

Do you have pictures..:)

Did you make several frames and butt them side by side all the way around the 3 walls or did you leave gaps?

HH

HuskerHarley
Do you have pictures
Have a look at http://www.bobgolds.com/AbsorptionCoefficients.htm and scroll down about 85% of the way and click on all the links from
Jon Risch's Absorbers
through
Vshine's Wall Absorbers.
That should give you some ideas

Originally posted by BasementBob
HuskerHarley

Have a look at http://www.bobgolds.com/AbsorptionCoefficients.htm and scroll down about 85% of the way and click on all the links from
Jon Risch's Absorbers
through
Vshine's Wall Absorbers.
That should give you some ideas

Thanks for the link..:cool:

Lot's to digest there.

I get the impression that I don't need to cover entire front wall and not cover other 3 sides all the way around to ear height after looking through those sites...Very confusing based on info in this thread...:confused:

HH

HuskerHarley
This forum talks a lot about home theatre with 5.1 to 7.2 sound.
The links on my site include stereo for musicians.
I provided the links to show examples of manufacture of panels, not about placement, nor quantity.

By looking at the http://www.bobgolds.com/AbsorptionCoefficients.htm chart, should 703 2” FRK be the best solution for bass absorption but not overkill the high frequency?

Originally posted by loquatsoft
By looking at the http://www.bobgolds.com/AbsorptionCoefficients.htm chart, should 702 2� FRK be the best solution for bass absorption but not overkill the high frequency?

I believe the general consensus is that 2" material provides too much absorption in the mid-bass range. To adequately absorb high frequencies, a certain % coverage of wall surfaces within the room is required. Using the 1" material results in the desired performance; using the same amount of 2" material would provide too much mid-bass absorption and using less 2" material would start to provide too little high frequency absorption. This is the way I understand it, but I'd like to hear confirmation from someone with more experience.

Originally posted by loquatsoft
By looking at the http://www.bobgolds.com/AbsorptionCoefficients.htm chart, should 702 2� FRK be the best solution for bass absorption but not overkill the high frequency?

Do you mean 703 instead of 702? Owens Corning 702 is not a standard product.

The answer is "it depends." ;)

There is mounting away from the wall, which is always better for low frequencies. There is faced (FRK) vs. unfaced, where faced with the facing mounted towards the room will reflect high frequencies but absorb low frequencies.

And there is also a grain of salt to be taken with any absorption coefficient chart. While these are nearly always made using certified laboratory data, there is also a fair amount of variation in measured absorption coefficients using the standard Reverberation Room method. There is significant variation from lab to lab, and even variation for samples measured in the same lab. So consider the coefficients good to only one decimal place, even though they are given for two!

- Terry

Carlton,
Seems like OC 703, FRK 2" even outperform the 703 1" plain on the midrange.
Terry,
Will you recommend the FRK (Foil reinforced kraft)? "This facing consists of an aluminum foil laminated to a kraft paper backing reinforced with a fiber glass scrim (yarn)"

Here's a chart I made to try to choose between the 1" and 2" OC's.

But instead of helping, I think I'm jut more confused because I still don't know how much is too much and how little is too little.

703 plain 1" (pink line) is what I was origninally looking at, and it still looks fine in comparison...

http://tinypic.com/1fa3qg

It's only too much or too little in comparison to a furnished room full of people. You can't decide just based on these numbers. You have to know what your room needs, where it will be applied, etc.

I am not sure if his is covered elsewhere in the forum but I plan to use the GOM fabric on the 703 and used speay adhesive and works fine,I also plan to use the same fabric on the upper part of wall (above 2 panels of 703 ) my question- what method have those of you who have applied this fabric to the wall applied it I wastold I should use the same spay adhesive, but definitely not wall paper paste, any help is appreicated
Peter

I am not sure if this is covered elsewhere in the forum but I plan to use the GOM fabric on the 703 and used speay adhesive and works fine,I also plan to use the same fabric on the upper part of wall (above 2 panels of 703 ) my question- what method have those of you who have applied this fabric to the wall applied it I wastold I should use the same spay adhesive, but definitely not wall paper paste, any help is appreicated
Peter

I was so surprised by the mighty 703. It really works. Now I can enjoy the deep bass that I’m longing for and it allows my 12” sub to do its work. Thanks you all(including OC).

ptwood, will you let me know how you do it(GOM) once you figured it out?

I hae another question, I have seen recommendation to put the adsoring 703 style panels on lower portion of walls, I was planning to just do GOM glued to walls above but found pictures and references to use a poly batting material above and cover this with GOM, can anyone comment on what this does
Thx for any help, if this is way to go then won't ned to glue
Thx

I hae another question, I have seen recommendation to put the adsoring 703 style panels on lower portion of walls, I was planning to just do GOM glued to walls above but found pictures and references to use a poly batting material above and cover this with GOM, can anyone comment on what this does
Thx for any help, if this is way to go then won't ned to glue
Thx

Polyester batting provides additional sound absorption, though not as much as 703 for the equivalent area.

- Terry

Thank you Terry I appreciate your reply, would you suggest just going ahead using the batting in addition to the 703 (top portion of the wall and about 2 panels of 703 hung horizontally) or shall I check room and go from there,
also I have soffitts (6-7 inches vertical 18 inches, horizontal) all around the room as well as columns on the side and rear walls holding the surround speakers should these be filled with insulation (mineral wool, fiberglass batts...?) any suggestions
Thank you
Peter

DIY VS REAL TRAPS

Besides the obvious difference in cost between REAL TRAPS and DIY OC 703 designed Traps.

Do they both deliver what were after?

I want to save money but I'm not sure if the DIY route would deliver what the REAL TRAPS promise to deliver, are the REAL TRAPS using the same insulation or do they have something special inside to separate them from the DIY versions.

In my situation money matters but I don't want to waste it doing a DIY that won't deliver what I'm after...

Convince me that DIY is as good as REAL TRAPS or just a few percentage points away from being as good.

HH

The article “Room Acoustics: Acoustic Treatments- Absorption” is quite interesting. But the following statement get me all confuse. Maybe they use something more sophisticate than the OC703.
“Note that 1” acoustical panels only work down to 1000Hz which is above most of the primary vocal frequencies and thus just about useless in affecting vocal intelligibility. Two inch material gets down to 500Hz or so and 4” down to 250Hz. “
http://www.audioholics.com/techtips/roomacoustics/roomacoustictreatments3.php

-------------
Adam

Originally posted by loquatsoft
The article �Room Acoustics: Acoustic Treatments- Absorption� is quite interesting. But the following statement get me all confuse. Maybe they use something more sophisticate than the OC703.
�Note that 1� acoustical panels only work down to 1000Hz which is above most of the primary vocal frequencies and thus just about useless in affecting vocal intelligibility. Two inch material gets down to 500Hz or so and 4� down to 250Hz. �
http://www.audioholics.com/techtips/roomacoustics/roomacoustictreatments3.php

-------------
Adam

Hi Adam,

It's not the material (703) but the way in which it is mounted which makes a huge difference in bass absorption. That article assumed you were mounting the absorber right against the wall ("A" mounting). If it is spaced away from the wall, the extra depth provides a very effective way to absorb the longer, low-frequency wavelengths. Ditto for corner mounting, which gives a continuous range of depths.

- Terry

I'll let Ethan describe exactly how the RealTraps are put together since it's his product.

Also understand that the recommended mounting for RealTraps is @ 45 degrees across a corner or at a tri-corner. They can be mounted other places but will not yield the bass absorbtion in that confiburation.

Standard 703 will also yield good bass trapping when placed @ 45 degrees across a corner.

Need some help from the experts on 703 vs 705 when I look at the ascoustical numbers comparing the 703 3#pcf vs 705 6#pcf the numbers don't llok all that much different for the 1" thick material, and the NRC value of plain (no facing) 703 is .70 and plain 705 is .65 (these nubers are when material is placed against a solid backing
willthe denser 705 be better - to get good numbers in the 125 and 250 octave range the 2 inch thick material 703 or 705 do much better
any comments pls
Thx
Peter

Need some help from the experts on 703 vs 705 when I look at the ascoustical numbers comparing the 703 3#pcf vs 705 6#pcf the numbers don't llok all that much different for the 1" thick material, and the NRC value of plain (no facing) 703 is .70 and plain 705 is .65 (these numbers are when material is placed against a solid backing
willthe denser 705 be better - to get good numbers in the 125 and 250 octave range the 2 inch thick material 703 or 705 do much better
any comments pls
Thx
Peter

You need to do the reverb calculation for your room and see if you need better bass numbers (125Hz and 250Hz) or not. All depends on the overall treatment, furnishings and architecture of your room.

There is no such thing as better numbers when it comes to acoustical treatment - rather are the numbers what you need, or can you revise your treatment to make the numbers fit your room based on what you can get.

Also consider that a 0.1 delta in numbers is meaningless - combined with corner-backed vs. hard-backed treatment are entirely different numbers. Good luck getting standardized corner-backed numbers - as no standard exists for that measurement!

Adam,

> Maybe they use something more sophisticate than the OC703. <

You bet we do. :D

But as bp explained, all bass traps work best in the corners, or at least near the corners.

--Ethan

Peter,

> will the denser 705 be better <

As Kras explained, minor differences are irrelevant, especially if you're comparing materials from different manufacturers who likely tested their products in different acoustic labs. Even though all certified labs should measure similar numbers for the same material, in truth the numbers can vary quite a lot.

Acoustics labs sometimes do a "round robin" test where the exact same samples are sent from lab to lab, and measured in each, to see how far the labs deviate from one another. The variations are a lot larger than we'd all like to think. At low frequencies in particular the numbers can vary wildly, even for tests run one right after another in the same lab on the same day. I've even seen negative absorption numbers reported!

Below is a link to a report I wrote recently that shows my own tests comparing the low frequency absorption of 701, 703, and 705, both faced and unfaced, using a different measurement technique than labs use. Although these tests do not give absolute absorption in Sabins, I'm convinced they're far more reliable than the tests run in acoustics labs for assessing relative absorption. Here's the link:

www.ethanwiner.com/density/density.html

--Ethan

Ethan,

Interesting read.

Your ETF measurements are maxing out at 100dB. It assumes the max response is that for each graph unless a SPL meter has been used to calibrate the mike reading and entered into ETF. This would make the charts more comparable.

Great thread guys. It has taken a couple of weeks, but I now have made it through the entire 17 pages of the post and know a lot more about this subject than I ever thought I would. The post has caused me to have four more questions that hopefully, you experts can field. As a matter of background, I have a bonus room with a HT/Stereo in it (TAW 3 chip, Theta Casablanca, Vandersteen, etc). This is not one of those dedicated jobbies like most of the guys on this post are doing. It started out as a bonus room and it is still a bonus room, though I am taking it over bit by bit. I use it quite a bit more for HT than for music (now that we can watch "24" and the like in HD on the big screen, usage has gone up! But I am far more critical of the sound with music. I would never think of giving up anything on the music front for the HT. I am getting around to the acoustic treatment part of the program and read this thread. So here are my questions. Your insight is appreciated.

1. On the subject of the OC 703/back and side walls/music vs. HT and you can't have both...I read in one of the posts that the 705 was a little more reflective and absorbed bass better. Wouldn't I possibly prefer it to the 703 on the side walls if music is important?

2. I know a lot more than I did before I read this thread, but I am by know means more sure of myself. Would it not be smarter to just pay an expert to come look at my situation and tell me what to do? OR....

3. Instead of planning this thing out to the hilt, considering the fact that I can screw up two ways...too much OR too little dampening...why wouldn't I just design it as I go. In other words, why wouldn't I put some panels on the back and the sides (first reflection included), then I listen to it. See it I like it. And if I don't, put on some more. Then I put in a bass trap, see if I like it and if I don't, put in some more. I am pretty much thinking that I will standardize on some sort of frame size like 2 X 8 feet. And finally,

4. The right side of the room (9 1/2' X 23') is completely void of any insulation. Upon banging on it, it acts like quite the bass drum. Seems to me like this can be a problem and/or an opportunity. Should I fill this wall with insulation? Will it do any good? I am thinking that it will slow that wall down from acting like a drum and if I am lucky make it act like one of those bass traps that Ethan was talking about.

Thanks in advance for your advice.

Randy

Kras,

> Your ETF measurements are maxing out at 100dB <

Yes, and not calibrating the mike with the room empty was on purpose, to better show the relative change in both response and mode bandwidth. I considered running the tests calibrated and uncalibrated, but that would have taken me six hours instead of "only" three! And I'd have had twice as much fiberglass all over my clothes. :D

--Ethan

Randy,

> Wouldn't I possibly prefer it to the 703 on the side walls if music is important? <

I asked a friend of mine who is a pro studio designer this exact question, and he says he uses 705 everywhere even though it's a tiny bit less absorbent at the highest frequencies. His reason is because 705 is easier to work with and looks better (corners better defined, etc.) and is easier to spray-glue fabric to. But in theory you are correct that 703 has a small advantage over 705 when the goal is to absorb first reflections.

> Would it not be smarter to just pay an expert to come look at my situation and tell me what to do? <

Sure, and the decision is based entirely on how much you're willing to spend on the project.

> why wouldn't I just design it as I go <

Well, you need to establish the room dimensions before anything else, and you can't easily fix bad dimensions after the fact. But you can certainly add bass traps and the first level of absorption, and then decide later if more absorption is needed and add it in stages.

> The right side of the room (9 1/2' X 23') is completely void of any insulation. Upon banging on it, it acts like quite the bass drum. Seems to me like this can be a problem and/or an opportunity. <

It's a problem, but it can be fixed by placing fluffy fiberglass against the wall on the other side. A flexing wall can act as a sort-of bass trap, but it needs to be damped to give the most benefit. It won't be as good as a purpose-built trap, but all bass trapping is welcome.

--Ethan

Ethan Winer

But those measurements are not relative - they are scaled.

Assume you measured the empty room and the max modal peak was 100dB.

Assume you put in the bass traps and damped down the max modal peak to 80dB.

When you measure again with ETF with the bass traps - the max modal peak will be again 100dB.

The max peak in ETF is always 100dB without calibrating with the SPL meter. Otherwise it has no idea what the sound card numbers mean - and it does not relate subsequent measurements to prior measurements.

Look closely at your charts - they are all max peak 100dB (sometimes right at the last frequency so hard to see)

So the charts are only relative with themselves - not each other. So the charts can tell you that the second highest peak is 20dB less than the highest peak on the same graph. But they cannot tell you is did this or that fiberglass - raise or lower the peak by 6dB?

Ethan-

Thanks for the response and the help. I think what I am going to do is use my 703 for bass traps and first reflections, and then when I need to buy more for phase two, I will use 705.

A couple of follow ups.

First, what is a ballpark amount for a designer to come advise me as to what to do?

Second, as far as the wall with no insulation (I didn't say, but I meant inside of the wall), I don't have access to the other side, but I can access the inside of the wall. Wouldn't I just want to take regular un-face batting and stuff it down in there?

Thanks for your help.

Randy

audiguy

You can find audio calibrators at www.homeacoustics.net that can plan/measure your acoustic treatment. Expect to pay more than your average AV wire puller would make. The most basic service offered is the Acoustic Design Review - they will just go over your room plan and make up a checklist of the most important things to do in your room.

Originally posted by krasmuzik
Ethan Winer

But those measurements are not relative - they are scaled.


hey kraz, everybody

if i can offer a thought: they are both

the scaling to the 100dB default for uncalibrated mic makes them scaled, yes, but you can still observe the decay rates at each of the modes and compare them relatively.

you can also still see (and i'm sure ethan's files would let this be explored more by him) the relative sharpness/roundness of the modal peaks and nulls

and i think that Ethan's experiment accomplishes his goal of relative comparison. Or, a better way to put it would be how he did in some post or other "a first step" towards understanding these twin phenomenon - FRK and density.

i like Ethans test, from what i gather in the description on his page, they took care to ensure that they changed one variable here, and not many.

g'day all

Brian

Kras,

> So the charts are only relative with themselves - not each other. <

I understand fully everything you said. But - right or wrong - that wasn't the way I approached this. I used ETF's normalizing as a feature to better center (vertically, on the graph) the relative change between the different materials. And by keeping the peaks higher on the graph I can better see the decay times. Believe me, I know how to use ETF! :D

(Well, much of it, anyway...)

> So the charts can tell you that the second highest peak is 20dB less than the highest peak on the same graph. But they cannot tell you is did this or that fiberglass - raise or lower the peak by 6dB? <

My intent was not to look at the change in peak height and null depth! It was to emulate a reverb room by measuring the change in decay time as a way to assess absorption. If I ever do this again I'll try it your way too and see if that shows the differences better than how I did it.

--Ethan

Randy,

> what is a ballpark amount for a designer to come advise me as to what to do? <

I have no idea. That's pretty far afield from what I do.

> Wouldn't I just want to take regular un-face batting and stuff it down in there? <

Yes, exactly.

--Ethan

Brian,

> i think that Ethan's experiment accomplishes his goal of relative comparison. Or, a better way to put it would be how he did in some post or other "a first step" towards understanding these twin phenomenon - FRK and density. <

Thanks.

--Ethan

Ethan

If things are just shifted to max 100dB - then the decay times are still valid. But if they are scaled to max 100dB then they are not.

Lets assume that the real SPL peak was 60dB and it decayed to nothing in 1s. Thus RT60 for that mode is 1. But in ETF it reads the SPL peak of 60dB as 100dB max since it has no idea what the real SPL is - but it does not scale time so it still decays to nothing in 1ns. But that means RT60 for that mode from ETF is 0.6s - even though in SPL terms it is 1s.

I like the idea of the experiment - it is just I don't know what to conclude from it because I don't see how any of the graphs are comparable with other graphs - as none of them have the same scale.

To me this is like using autoscale in Excel Graphs - but then leaving the Yaxis labels off.

Maybe I am misunderstanding and TF dB steps DO correlate to SPL steps - but it just does not know the peak value to use without calibration (better to represent peak as 0dB then - and everything else as -dB from peak). Maybe this is something Doug from AcoustiSoft can answer.

hey again everybody,

the decay times, as viewed on the bottm of the plots can be skewed, yes, by this scaling.

however, what we want is the decay rate, or in a waterfall, for example, the # of decibels of decay per line of time coming toward you. And those comparisons - and there are some cases on EW's density page where it is obvious that things are faster - are still valid relative to one another.

i do not consider it impossible to attain a sabin figure from non-reverb room tests, but that's a wild tangent to this topic and i've not the time this evening.

pleasure reading everybodies thoughts,

Brian

Brian Ravnaas

the # of decibels of decay per line of time coming toward youIsn't krasmuzik's point that because the y scale is dynamic, you don't know the # of decibles of decay per line.

hey bob,

because the scale is random, the time (# of lines) where the decay enters the "floor" of the graph is misleading.

but waterfall plots do not innately skew the decay rate. Decay rate is not related to where any given peak enters the floor of the graph, but is related to the db/time, or db/line going forward.

you can't count lines starting at the top of the peak, you have to count the lines over some amount of decay, which you can loosely diving by drawing lines parallel to the various axis.

more ideally, you would calibrate the mic or find some way to make ETF (or alternate software) deliver a more direct answer as to what this decay rate was.

And i konw this topic borders, in places, on being so controversial that nobody even wants to talk about it or think about it, they just want it to be XXX or YYY, but... take a look at the definition of a sabin, and how it's calculated in ASTM C-423...

Brian

Brian Ravnaas

Just in case we're talking apples and oranges, I've made this little graph to show what I'm talking about.
By slope alone the graph on the right appears to have a larger decay rate when viewed on an ETF5 'artificial 100db all peak' scale (sub rights), but knowing the Actual Db scale (sub lefts), I think the graph on the left has the higher 'Actual' decay.
i.e. the left decays at 50db / 6 units of time, and the right decays at 8db / 4 units of time.

http://www.bobgolds.com/ETF_decay.jpg


more ideally, you would calibrate the mic or find some way to make ETF (or alternate software) deliver a more direct answer as to what this decay rate was.Yea, that would be great. :)

Brian's right about the slope of a mode (dB over time) in a waterfall chart indicating its decay rate.

Bob, I'm afraid your example graph isn't right because dBs are logarithmic and scale by addition, not multiplication.

- Terry

Terry Montlick:

Brian's right about the slope of a mode (dB over time) in a waterfall chart indicating its decay rate.Yes, but it assumes that you know the db otherwise you don't know the slope.

With ETF5 waterfalls the y axis scale is always converted so that the peak is at a fake '100dB'. In my graphs I didn't show that peak, so above please assume that '100db' mark is somewhere else not shown on the graph, and that what is shown is two other peaks merely provided to show that the visual slope is independant of the actual slope/decay rate.

My point is that if you have two independant measurements (two ETF5 test runs), and are looking at the visual slope on the waterfalls, they can't be compared from one waterfall chart to the next waterfall chart because you don't know the real slope because the y axis isn't fixed/constant between them.

Within a single waterfall chart two peaks could be compared because the slope would be consistant, but that's not what we're doing today.

Bob, I'm afraid your example graph isn't right because dBs are logarithmic and scale by addition, not multiplication.I know dBs are logarithmic, but I'm afraid I (just me) don't follow that sentence. :confused:

hey bob,

the dB on the sides aren't the CORRECT values, for example, 100dB might actually be 77 or 89 or 107

but the decibel increments on the graph (each 3dB line) do represent 3dB.

hence the decay rate from picture to picture can be assessed.

it would be preferable to use another function of ETF to assess the decay rate in a more formal way, but the waterfalls do reflect the decay in a consistent manner from graph to graph. with the exception of how high on the plot each given mode/decay starts - that is arbitrary.

Originally posted by BasementBob

...
I know dBs are logarithmic, but I'm afraid I (just me) don't follow that sentence. :confused:

It means that when ETF scales the y axis so that the maximum is 100 dB, it does so by adding a fixed number of dBs to the graph. As Brian said, a 3 dB change is always a 3 dB change. So scaling a graph upward by 30 dB means ADDING 30 dB to every point in the graph, not multiplying it by some factor.

- Terry

Bob,

> Isn't krasmuzik's point that because the y scale is dynamic, you don't know the # of decibles of decay per line. <

The height is labeled in dB so I don't understand the problem. Maybe I could have set the range to span from 100 dB down to 60 or even 50 dB, then set the time out to a full second to see more of the decay. I guess I can still do that since I have all the original ETF files.

Coulda / shoulda - hey, I gave it my best shot. I never claimed this was the be-all end-all low frequency absorption test. :D

Please don't shoot the messenger. We're all on the same side here, trying to learn more about this stuff!

--Ethan

Brian Ravnaas, Terry Montlick, Ethan Winer

How do you know that a 3dB change in ETF - is indeed a 3dB SPL change?

Are you sure ETF (or mic input) does not have a gain expander function in there - as in the minimum reading is 0dB and the maximum reading is 100dB? Thus 3dBETF!=3dBSPL?

krasmuzik
Are you sure ETF (or mic input) does not have a gain expander function in there - as in the minimum reading is 0dB and the maximum reading is 100dB? Thus 3dBETF!=3dBSPL?

The minimum on the ETF5 waterfall charts is always 70db.
The maximum on the ETF5 waterfall charts is always 100db
There are always points on both.

So I'll rephrase what you wrote a bit

"Are you sure ETF (or mic input) does not have a gain expander function in there - as in the minimum reading is 70dB and the maximum reading is 100dB? Thus 3dBETF != 3dBSPL ?"


BTW, Terry, Brian, Ethan -- I get what Terry meant now. Thanks. :)

Originally posted by krasmuzik

Are you sure ETF (or mic input) does not have a gain expander function in there - as in the minimum reading is 0dB and the maximum reading is 100dB? Thus 3dBETF!=3dBSPL?

Yuck -- that would be a pretty nasty feature (bug!).

The waterfall plots go from 70db to 100db, but signals 'flat-line' at 70 ie. you can infer that the levels were measured to go below that the GUI just wont let you see it. Other plots will let you go below 70db.

If there was a 'normalization' function going on I would be really annoyed :) You cant tell what the absolute SPL is at any frequency but I still believe you can tell it is exactly #dB larger than the frequency next to it.

It could be a nasty feature of the sound card mic/line input - I use the ETF mixer which is supposed to bypass everything - but you can never be sure. ETF only cancels out frequency response errors with the feedback channel- but can never know if there is auto/nonlinear gain on both channels.

Yes indeed the waterfall plots have a waterline - just makes it easier to see the mountains without all the garbage on the ocean floor.

I sure hope it is the case the delta dBETF = dBSPL - but I have not seen any tests that (dis)prove that. Maybe this only occurs with SPL calibration in ETF.

For doing reverb/modal decay and Sabine calculations that would be important - but for just doing continuous measurements to see relative impact of a panel should not matter as long as you are aware of the dB shift to max peak=100dB.

But this max=100dB feature can get you into trouble - suppose you build a resonator to target a peak mode as some on here have been attempting. In reality the resonator could be successful at killing the peak - but now some other peak is at max=100dB - leaving you scratching your head - as that peak was not there before! Even though in reality the peak SPL dropped from 100dB to 80dB.

I have not checked continuous mode to see if it scales up to max 100dB. It seems it could use differences between readings to make better relative scales - at least within the same ETF session - so that you have max=100dB only once per session rather than per graph. But that would require that successive runs be able to show >100dB. Then the user would have to watch out for the continuous graph scale changing - which could itself be misleading.


So I still think it is worth doing the SPL calibration!

Bob,

> The minimum on the ETF5 waterfall charts is always 70db.
> The maximum on the ETF5 waterfall charts is always 100db

Not so! When displaying a waterfall graph, click the icon at the lower far-left of the window and you can set both limits to anything you want. That's why I suggested yesterday that maybe I should display my Density graphs again setting a new lower bottom limit to better see more of the decay.

--Ethan

Kras,

> suppose you build a resonator to target a peak mode as some on here have been attempting. In reality the resonator could be successful at killing the peak - but now some other peak is at max=100dB - leaving you scratching your head <

I agree with that completely. But again, my goal was to see the change in decay rate versus frequency, not changes in absolute level.

I promise the next time I do a test like this I'll either do it your way, or run it both ways. Okay? :D

--Ethan

Originally posted by Ethan Winer
Bob,

> The minimum on the ETF5 waterfall charts is always 70db.
> The maximum on the ETF5 waterfall charts is always 100db

Not so! When displaying a waterfall graph, click the icon at the lower far-left of the window and you can set both limits to anything you want. That's why I suggested yesterday that maybe I should display my Density graphs again setting a new lower bottom limit to better see more of the decay.

--Ethan

that would be very interesting, Ethan.

also, are there any other means of presenting the data? like a frequency-filtered (filter between two of the nulls) "o-scope" view that would let you see the decay over time at a given frequency?

My God Brian - don't you ever sleep!?

Brian,

> a frequency-filtered (filter between two of the nulls) "o-scope" view <

No, ETF offers only a few fixed ranges. If it did allow setting any arbitrary upper and limit limits, that would solve the problem I mentioned to you this morning in alt.sci.physics.acoustics, about some peaks being hidden behind others.

--Ethan

Ethan,

i guess the possible analogy with assessing mechanical damping via individual modes and peeking at absorber performance via individual modes has kind of intrigued me through all this discussion.

i understand if you're not interested, but you can mail me at brianravnaas@audioalloy.com, and if you don't mind emailing the files (i'm sure they are huge) i'll take an hour and try to process them on some equipment here at the lab. ASCII files or .wav files, if they are possibilities.

just a thought, and just for my own curiosity.

Brian

Brian,

> if you don't mind emailing the files (i'm sure they are huge) i'll take an hour and try to process them on some equipment here at the lab. ASCII files or .wav files, if they are possibilities. <

The 13 files I have are native ETF data files, and each is about 790 KB. If you have ETF I'll be glad to send them to you so you can do whatever analysis you'd like. But if you don't have ETF these files will be of no use.

--Ethan

Originally posted by Ethan Winer
Brian,

The 13 files I have are native ETF data files, and each is about 790 KB. If you have ETF I'll be glad to send them to you so you can do whatever analysis you'd like. But if you don't have ETF these files will be of no use.

--Ethan

i've got no ETF, so i guess for now i can't do anything.

Brian

I have been reading through this thread and although I have gleaned a ton of great information, I don't think this question ever got answered definitively (pg.3 of the thread). I have seen one response saying it doesn't matter if you treat above ear level at all (its only for aesthetics) and another which says it is part of the sound characteristics of the room. Which is it? I would love to just paint that part of it and be done.

Originally posted by smithb
I really could you use some advice based on the following questions:

-----------------------------------------------------------------------------------------
I am very interested in an answer to "gjlowe" question:

"if you put a ledge molding instead of chair rail around the walls, do you even need treatment on the upper half?"

My plan is to treat the whole lower half (ear level and below) of the room as suggested (except full treatment on front wall). However, I have read mix messges on the value of using cloth covered batting on the top. Some say it is for acoustical purposes and some say that it just pushes the upper wall out to meet the treatments of the bottom half. I personally would like to just paint the top half and build a ledge in the chair rail to save money if batting doesn't add any additional value. So which is it?

What is the rule about hanging pictures on the upper walls?

Some treat the lower half of columns and others do not. Is there a reason to go one way or the other?

I see many putting heavy curtains along the front wall which looks very nice. What impacts does this cause on the front wall treatment? No impact or cancel it out?

Finally, do people treat the wall area behind the screen?

Thanks for any feedback.
-----------------------------------------------------------------------------------------

Any response from the experts would certainly be appreciated: Dennis or Eric?

strange_brew,

Batting is definitely not just for aesthetics. It provides significant sound absorption.

Whether or not you need it depends on your room. There is no "one size fits all" in room acoustics.

For example, suppose your front speakers are mounted high up, and the first reflection points between speakers and ear are above the level of the fiberglass treatment. Then you definitely want to put up polyester batting (or additional fiberglass) to absorb these reflections.

On the other hand, if the fiberglass itself provides the right amount of absorption for correct reverberation times, adding batting may over-absorb high frequencies.

The only way to know is to test and/or computer model your room.

Regards,
Terry

Thanks Terry.

Then I'm guessing that in most cases it must be required from the number of theaters (particularly DE designs) that include it. I suppose that answers another of the questions that has been bothering me as well - when I look at many of the professionally designed theaters (again, mostly DE designs), it looks to me like the lower "insulshield" portion is lower than ear level? Or maybe its just hard to tell from the screenshots I have seen.

To be honest I glossed over much of the thread that dealt with computer modelling the rooms since what I gathered (particularly from Dennis' posts) is that it just depends too much on people, furniture etc... as those things become a large portion of the volume of the room. And I don't know that i'm up for trying to Ray Trace my room. Obviously this is where the value of hiring a pro designer comes in, but if by mimicking rooms similar to mine I can get 80% of the way there, I'll probably be happy.

Craig.

Craig,

> I have seen one response saying it doesn't matter if you treat above ear level at all <

See my first reply in this thread:

www.avsforum.com/avs-vb/showthread.php?s=&threadid=507497

--Ethan

Thanks Ethan. I think I'll follow the crowd on this one and go with the Polyester batting and GOM.

Hello,

I have been reading and learning a lot. Thank you very much for all your time you put into this.

Here are two pictures of my dedicated home theater that is in the beginnings of construction by me. I am interested in your thoughts about my design? I have some options right now while under construction.

1) Most dedicated home theaters I see pictures of have the front speakers close to the screen. Am I making this more difficult by trying to have the speakers far forward for an equilateral triangle? Complicates #2 below.

2) As it stands now, I would have to go behind the speaker to access the equipment. AV equipment can be moved toward the screen more and not have a corner trap. Or back and then move the speaker toward the screen. Thoughts on this.

3) Are the rear surrounds placed in the room properly with the door and walkway to the seating? Door can be moved only back. If I move it back further is there any advantage?

To answer these questions more fully, I know you will need the RT60 and the sound adjustment ideas. I am working on the RT60 calculation and so far it looks like this:

Preliminary results from Chris Whealy's 2004__V 2.61

1.5? Ductboard with Foil facing NRC =.90
Frequency___________125Hz___________250Hz___________500Hz___ ________1KHz___________2KHz___________4KHz
Sabine_______ _ _ _ _ ___0.43___________ __0.43__________ _ _ 0.27______ _ _ _____0.21__ _________0.23________ ___0.21
_
1? Ductboard with Matt facing NRC =.70
Frequency___________125Hz___________250Hz___________500Hz___ ________1KHz___________2KHz___________4KHz
Sabine___________ _ _ _ _0.45___________ _ _0.56___________ _ 0.36_______ _ _ ____0.26___________0.23_________ ___0.21

Room details:
I currently have the 1.5" and 1" ductboard.
Room size 88.25" H x 139.75" W x 235"L (in basement). Room Volume 1,677 ft3
Fabric covered Insulation on Lower 48? side wall coverage and entire front wall
Upper side walls and back is painted
Ceiling and walls are basic 1/2" drywall, no insulation in Ceiling, walls have R-13 in standard wood studs.
Carpet is a shag with a 1/2" pad over concrete
Seating is one large cloth pillow back sofa 110" x 36" (4 seats) plus two ottomans (18" x 31")
Door is a can be either hollow or solid core?
AV equipment will have a glass door over the front of it (approximately 60" x 18")
Screen is 96" wide and is Gatorfoam painted.
Projector AE700, ceiling mounted

Thanks for your help,

Kevin

Here is the speaker firing diagrams to go along with the top down view in previous post.

Thanks, Kevin

Question regarding OC703 on my front wall.

My plans include covering the front wall with OC703. I'll have a false wall about 30" out from that covered in black GOM FR701 fabric. My L/C/R speakers and my sub will be behind this false wall. My RPTV will be recessed into this false wall.

Should I cover the OC 703 on the wall to keep the fiberglass from possibly becoming airbourne inside this false wall area? I've never seen OC703, so I don't know if this is a valid concern or not.

It's fairly well-contained as far as fiberglass goes, fluffy insulation seems to let loose a lot more fibers, it seems that the fiberboard tends to release fibers mainly with physical contact, so you should still wear gloves. I have an MD in the family, so I definitely made sure to cover all the fiberglass to keep from breathing it in, but if you have a false wall covered in fabric, I think that barrier is relatively effective for that unless there is a lot of air blowing around in there.

I'm really not qualified to know, but my common sense tells me that you'd at least avoid having bare fiberglass in areas where people are, or where there are air vents and such.

I haven't tried 703 nor linacoustic, but with Roxul's rigid rockwool I found that when I carried some around with my bare hands that eventually my hands started to feel prickly and turned red. Nevertheless I'd say the effect was much less than I've had on exposed arms (holes in workshirt near buttons at wrists) and neck when I've worked with fluffy insulation insulating a house and attic. Also some little pieces (1/4") and dust fell off when the Roxul panels were moved or bumped. Thereafter I handled it with rubber gloves and a jumpsuit.

Originally posted by Toeside
Question regarding OC703 on my front wall.

My plans include covering the front wall with OC703. I'll have a false wall about 30" out from that covered in black GOM FR701 fabric. My L/C/R speakers and my sub will be behind this false wall. My RPTV will be recessed into this false wall.

Should I cover the OC 703 on the wall to keep the fiberglass from possibly becoming airbourne inside this false wall area? I've never seen OC703, so I don't know if this is a valid concern or not.

Hi,

I used coated Insulshield behind my fabric false wall and I've never experienced any problems with airborne fiberglass. As Chris cautions, there were no air vents behind the false wall.

Larry

I don't have any vents where my false wall will be, so that's not a concern.

However, I am concerned with the air movement caused by the sub that will be behind the fabric wall.

I think I'll try to find insulshield locally (there's a place to get OC703). If I go the OC703 route, maybe I'll cover it with fabric to be safe.

Originally posted by Toeside
I don't have any vents where my false wall will be, so that's not a concern.

However, I am concerned with the air movement caused by the sub that will be behind the fabric wall.

I think I'll try to find insulshield locally (there's a place to get OC703). If I go the OC703 route, maybe I'll cover it with fabric to be safe.

Hi,

I've got a decent size subwoofer and full range main speakers behind the fabric false wall, and still no problems.

Larry

From this thread, it seems that curtains can help with high frequencies, but not really low frequencies. In my case, I plan to put a large front projector screen in front of an even larger set of picture windows. I could pull thick drapes across when using the room, but would the windows still severely damage the sound quality?

Is there anything I could do with other materials, while still having the option of seeing out the windows when I wasn't using the projector?

What about the idea of angling the windows a bit so that the reflections go to the sides instead of straight back to the viewer/listener?

Originally posted by Erikb
From this thread, it seems that curtains can help with high frequencies, but not really low frequencies. In my case, I plan to put a large front projector screen in front of an even larger set of picture windows. I could pull thick drapes across when using the room, but would the windows still severely damage the sound quality?

Cheap, wimpy curtains won't do much. But heavy velour drapes of 18 ounces per square yard, hung in loose folds, provide pretty good sound absorption:

absorption coefficients (from L.L. Beranek's "Acoustics")
0.14 at 125 hz
0.35 at 250 hz
0.55 at 500 hz
0.75 at 1000 hz
0.70 at 2000 hz
0.60 at 4000 hz

Theatrical supply houses stock this really heavy material. I use Georgia Stage -- www.gastage.com.

- Terry

Thanks, Terry. That was exactly what I was looking for.

Your reply also led me to find this book:

Noise and Vibration Control Engineering : Principles and Applications
by Leo L. Beranek

which has some great additional information (found using the "search inside this book" feature at Amazon).

I have ordered some 1" OC 705 for my front wall. I will have enough to put some behind my screen, (92" Da-Lite HCCV, non-perforated). The screen is mounted 3" off the wall, so I could get some in there, but is it even worth doing if the screen is non-perf'd?

Also, what is the recommended mounting method for OC 705? It will be covered by burgundy velvet drapes, so it won't be seen.

Thanks,

Craig

Originally posted by craig john
I have ordered some 1" OC 705 for my front wall. I will have enough to put some behind my screen, (92" Da-Lite HCCV, non-perforated). The screen is mounted 3" off the wall, so I could get some in there, but is it even worth doing if the screen is non-perf'd?

Hi Craig,

If the screen is not micro-perforated, then it's not worth putting fiberglass behind. The solid screen would reflect frequencies above a few hundred hertz. But below this frequency, the absorption ability of even 3 inches of fiberglass falls off significantly. So you'd end up with an absorber peaking at a few hundred hertz.

- Terry

Originally posted by Terry Montlick
If the screen is not micro-perforated, then it's not worth putting fiberglass behind. The solid screen would reflect frequencies above a few hundred hertz. But below this frequency, the absorption ability of even 3 inches of fiberglass falls off significantly. So you'd end up with an absorber peaking at a few hundred hertz.


Hi Terry,

What about a non-perforated screen that is 24" off of the wall?

I have my screen mounted across a recess that is 24" deep. There is 18" of space over and 22" of space under the screen for sound to get behind it.

Plan View (http://mysite.verizon.net/res8ycu4/sitebuildercontent/sitebuilderpictures/plan.gif)

Front View (http://mysite.verizon.net/res8ycu4/sitebuildercontent/sitebuilderpictures/front.gif)

I have 1" of Insulshield covering the entire front wall, including the insides of the recess. I would like to add more insulation to improve the bass response, but I feared that it might make the room too dead at the mid and higher frequencies. I've attached a graph the Reverberation Time of the room, which you can see is fairly low.

However, I had not considered that the screen might reflect most of the mid and high frequencies traveling to the recess. Do you think adding 2-3 more inches of insulation in the recess behind the screen might make the room too dead. The recess is roughly 7' wide by 9' high. The room is 15' wide x 26' long (including the recess) x 10' high.

Thanks.

Larry

Originally posted by LarryChanin
I would like to add more insulation to improve the bass response, but I feared that it might make the room too dead at the mid and higher frequencies. I've attached a graph the Reverberation Time of the room, which you can see is fairly low.

However, I had not considered that the screen might reflect most of the mid and high frequencies traveling to the recess. Do you think adding 2-3 more inches of insulation in the recess behind the screen might make the room too dead.

It would be fine, Larry. It should only affect the low frequencies, because your screen is already reflecting the highs.

- Terry

Terry

Have you done the calculation of vinyl movie screen (nonperf) over fiberglass as a membrane bass trap? One of the things on my list of things to do.

Will the spray glue on the GOM and 703 wreck any of the acoustic capabilities of either?

Is it necessary to glue the two together?

I was hopping to be able to just use staples but I've read that most seem to spray glue on both materials and I am concerned that it might cause a reflection instead of absorption????


Husker

Well.. I finally picked up some OC 703, and I'm still waiting on my GOM fabric samples.. so I can't make my panels and bass traps yet.. but for the heck of it, I decided to place some on the wall and behind my screen anyway... Now I wish I could do a simple A/B, panels off panels on quickly ... but with DVD's I'm very familiar with I noted the following...

1. Significant dialouge improvement from center channel (B&W Matrix HTM), I had to turn the level down 2 levels (had it +3 compared to front channels)

2. Surround speakers much more defined, and localized. Example, when listening to Bugs life.. I heard the ambient rear surround channels much more distincly..

3. The room just sounds much more dead... don't know how else to say it, it's just not alive as it used to be...

I haven't done a frequency response comparison of the room yet... I only use test tones and Rat Shack SPL meter...

Overall, the sound is just more defined, and I can better tell from what speaker the sound is coming from.. I woudl say that's the biggest difference. I couldn't play anything too loud to tell any bass differences...

Originally posted by krasmuzik

Have you done the calculation of vinyl movie screen (nonperf) over fiberglass as a membrane bass trap? One of the things on my list of things to do.

I'm not sure that this would be a good idea.

For one thing, you'd have to seal your screen to a box. Also, the very low frequency absorption wouldn't be great because of the hole size and hole/area ratio of the screen.

Having said that, here is the predicted 0-incidence response (transfer matrix method) of a 0.4 mm thick Stewart microperf screen covering a 1-foot deep box completely filled with uncompressed fiberglass batt. :)

http://www.tmlaboratories.com/micro-perf-absorber.jpg

Not a bad broad-band absorber, though I wouldn't call it a bass trap.

- Terry

Originally posted by HuskerHarley
Will the spray glue on the GOM and 703 wreck any of the acoustic capabilities of either?

Is it necessary to glue the two together?

I was hopping to be able to just use staples but I've read that most seem to spray glue on both materials and I am concerned that it might cause a reflection instead of absorption????


Husker


Please...;)

Husker

Originally posted by HuskerHarley
Will the spray glue on the GOM and 703 wreck any of the acoustic capabilities of either?

Is it necessary to glue the two together?

I was hopping to be able to just use staples but I've read that most seem to spray glue on both materials and I am concerned that it might cause a reflection instead of absorption????


Husker

A thick enough layer of spray glue could create some high frequency reflection. I'd avoid glue if possible, or confine it to the edges.

Originally posted by Terry Montlick

quote:
--------------------------------------------------------------------------------
Originally posted by krasmuzik

Have you done the calculation of vinyl movie screen (nonperf) over fiberglass as a membrane bass trap? One of the things on my list of things to do.
--------------------------------------------------------------------------------

I'm not sure that this would be a good idea.

For one thing, you'd have to seal your screen to a box. Also, the very low frequency absorption wouldn't be great because of the hole size and hole/area ratio of the screen.

Having said that, here is the predicted 0-incidence response (transfer matrix method) of a 0.4 mm thick Stewart microperf screen covering a 1-foot deep box completely filled with uncompressed fiberglass batt. :)

http://www.tmlaboratories.com/micro-perf-absorber.jpg

Not a bad broad-band absorber, though I wouldn't call it a bass trap.

- Terry

Hi Terry,

Kevin's question was in regard to a non-perforated screen.

Neverthess, very interesting information.

Thanks.

Larry

krasmuzik,

Sorry, I misread your posting. You asked about a non-perforated screen. I'll do the calculations for this, and get back to you.

- Terry

Here it is.

Identical to the earlier device I posted, but the screen does not have the perforations.

- Terry

http://www.tmlaboratories.com/nonperf-absorber.jpg

JM INSUL-SHIELD question.

Trying to buy and must buy a "unit" ie 48 pieces regardless of size. (I will use 2x4)

I assume I need the" knitted faced" but they come in densities ranging from 1.5 to 6.0 lbs/sq ft.

Which density do I need for lower 48 inch side walls and complete front wall? The theater is 12x20x9 ft.

Yes I have read the entire thread but after 18 months of house building I am in overload.

Bob,

> Which density do I need <

703 at 3 pcf is pretty much the standard for mid and high frequencies. Denser 705 at 6 pcf is better for bass trapping when using thicker panels mounted straddling the corners. And you really do need that too.

--Ethan

Density

Is the spec 3 lbs/cubic ft OR 3lbs/square foot as my supplier told me. Big difference ie 2x4=8 sqft x 3 = 24 lbs for one sheet. ??

Anyone using a different density?

3 lb/cu ft. If it were by the SQ FT, then you'd have different ratings for different thicknesses (1", 2", 4", etc.)

Some people use 6lb for bass trapping purposes. 3lb is a more genral purpose, all around good density for bass absorbtion, reflection points, etc.

bpape

OK then I should use 3 lb/cuft for entire front wall and lower 4' of both side walls?

mooney,

I put 1" OC 703, on my front wall ( behind my screen and velvet curtains), and put 1" OC 703 at my reflection points. I didn't put anything upto ear level, since I'm not doing the room from scratch, so only the reflection points. I'm doing these treatments after the fact.

Intially, I had only treated my reflection points, and I really liked the difference, as I posted above. This weekend, after also treating my wall behind my screen ( 1" OC 703 beghind screen and light duty velvet curtatins), I don't know.. I'm having 2nd thoughts, I have to try it without because it may be too dead.. Maybe the light duty velvet curtains were enough.. and for me the refletion points will suffice.. I just hate to take it all down again... :( to see what it sounds like without an treatment on my front wall....

First, let me apologize for my ignorance. I have tried to read this thread along with a bunch of articles on the web such as Audioholics, etc. I am trying to figure out how to acoustically treat my new home theater. I'm not stupid, honestly, but for some reason I just can't seem to figure out all this acoustical business. My new home theater is fairly big: 26x15x8. I don't have the furniture in yet, but it will be leather, which won't help acoustics much. I would like to improve the acoustics of the room for use with multi-channel sound.

My questions/concerns:

1. Can someone point me to a source that can help a beginner out with what is needed from a practical standpoint? I find the science/physics of sound interesting, but I don't really get it. I need a source of practical how-to information on how to treat the room. I need information on placement of panels, number of panels, reflection points, bass traps, materials, etc. In the end, all I want is to have a great-sounding theater.

2. I would prefer not to cover the entire surface of every wall. I have sconces already installed so that may also pose an obstacle. Further, I want to make sure that whatever is installed is aesthetically pleasing.

3. I don't want to spend thousands of dollars. Are there places out there that sell completed panels/bass traps at a reasonable price? I am willing to do some work myself to make them, but I am confused by all the different terminology and materials discussed.

Any help is appreciated!

Thanks,

Jonathan Schmidt

jschmidt

contact homeacoustics.net to find an audio calibrator in your area. They know the science and are familiar with treatment solutions.

Thanks, Krasmuzik. The nearest engineer is about an hour and a half away. (I live in a rural area.) I'll give him a call, but I'm worried about the cost of hiring someone like that. But, I suppose if I want it done right, I'll need the help.

If anyone else has any other suggestions, I would appreciate it.

Jonathan,

> it will be leather, which won't help acoustics much. <

Actually, a leather couch in the right place can help to absorb bass. However, it won't do much at mid and high frequencies. Moreover, the best place for acoustic treatment is where the reflections originate, which is the walls and optionally the floor and ceiling.

> I need information on placement of panels, number of panels, reflection points, bass traps, materials, etc. <

See the Acoustics FAQ, second in the list on my Articles page:

www.ethanwiner.com/articles.html

> I would prefer not to cover the entire surface of every wall. <

Nor should you!

> Are there places out there that sell completed panels/bass traps at a reasonable price? <

Yes. :D

--Ethan

jschmidt

HAA is to Audio techs much like ISF is to Video techs. They are not expensive acoustic engineers - they just have been trained on acoustic science so they stay away from audiophile voodoo that some AV places participate in. So they should give you bang for the buck solutions - maybe even just moving stuff around the room, or a list of things to get at industrial warehouses.. Most calibrators realize their market is limited to how far they can travel - I just did a three hour trip last weekend!

Of course there are several acoustic engineers and acoustic treatment companies that hang out in this thread who would be willing to help you.

Well, I got the estimate back from the place I was referred to by HAA. I'm not a good judge of whether ehtier pricing is reasonable, but it is definitely a LOT more than I was thinking. To start, they recommended the following:

* Seating and speaker placement modelling - $695
* Modelling of first order reflection points - $695
* Modelling of reverberation control (where to put the accoustical treatment and what size) - $1500

Mind you that this does not include any on-site visit. I would have to provide them with all measurements of the room. This also does not provide any actual accoustical treatment. Only provides a mapping of where the speakers and seats need to go along with a diagram of where the accoustical treatment needs to be applied.

I don't know about you guys, but spending nearly $3000 for no actual sound improvement to the room is not my idea of value.

Thanks, Ethan for the very informative article! When it comes to actually putting up some accoustical treatment, I will get some OC from my local HVAC company. I have a call into them to see if they can special order from 705-FRK. It's not something that they normally use for ducts. Instead, they typically use Enduragold, which does not appear to have the accoustical properties needed. Your article helped a ton!

Now I just need to find a cheaper way to figure out the first order reflection points to at least make sure those are covered... without spending $3000.

Originally posted by jschmidt

...
Now I just need to find a cheaper way to figure out the first order reflection points to at least make sure those are covered... without spending $3000.
That's pretty easy, unless somebody wants to sell you a $3000 mirror. ;) All you need is one other person and a mirror. Do a search on the forum - their are a number of discussions on the mirror method for finding the first reflection points.

- Terry

Jonathan,

* Seating and speaker placement modelling - $695
* Modelling of first order reflection points - $695
* Modelling of reverberation control (where to put the accoustical treatment and what size) - $1500

Mind you that this does not include any on-site visit.
Yikes, you can get all that for free on the Articles page of my company's web site!

--Ethan

For $3K you could buy a boat-load of Ethan's traps.

All this depends if you value your money more than your time. Everyone on here is always happy to educate - but you have to be willing to make the investment in time to learn. If you consider that calibration is normally charged at a higher rate than the guys pulling the wire - say $100/hr instead of $75/hr -their fees are not that unreasonable considering contractor overhead is usually 3x take-home pay. It probably takes half the time quoted - but you have to leave room for the back and forth on the design and multiple redos. You could look into Dennis and Terry on this forum to find out what they charge for design/calibration as they both work nationally.

* Seating and speaker placement modelling (1 day)

Good resources for this are Harman Kardon white papers, RPG Room Sizer/Optimizer, and CARA. To be most effective you will need to know the directivity and crossover data for your drivers.

* Modelling of first order reflection points (1 day)

Two people and a mirror, as already suggested. Don't forget to check all reflective surfaces - any soffits, ceilings, floors, stages, proscenium, columns, etc. This needs done in every seat for every front speaker. RPG Room Optimizer will do this for a rectangular room. You also need to know how much reflection to cut, and how much to keep (how deep - how long - how wide - in space and time)

* Modelling of reverberation control (where to put the accoustical treatment and what size) (2 days)

Here is where it gets difficult. You have to know the frequency absorption curves of your material and how much total to use in the room, to achieve what reverb time. Absorption varies depending on how much the edges are exposed and how far it is from the wall. SpreadSheets or CARA are useful tools for this.

BasementBob has been an avid collector of absorption data - his website is a good start. Don't forget that your carpet, chairs, risers, walls, stage, etc. all have variant absorption curves, as well as people.


Finally, what you were not quoted was calibration& verification of the design. This involves taking impulse or sweep measurements of the room. ETF5 is a popular program for this - mostly because it is free, unless you expect to save your work for later analysis or use a calibrated mike/preamp, or use useful special features.

What the HAA tech should have told you is they have a 50pt design checklist they can use on your room - this is always a good start with a site visit or floorplan review, and should be done for a much more nominal fee. If you have some fatal flaws in your room - you may want to fix those before pursuing treatment.

Originally posted by krasmuzik
You could look into Dennis and Terry on this forum to find out what they charge for design/calibration as they both work nationally.


I currently charge $95/hr for everything - acoustical device design, custom theater design, measurement, calibration, computer simulation from 3D DXF files using professional ray-tracing software, etc. Also 1/2 that rate for actual travel time. And of course, there's the Great Food Discount if you live in someplace like New Orleans. ;)

- Terry

...I charge extra for New Orleans. That way I have more to spend on food. ;)

Originally posted by Dennis Erskine
...I charge extra for New Orleans. That way I have more to spend on food. ;)

Okay, we can buy each other oysters at the Acme Oyster House. ;)

Regards,
Terry

For what its worth, I tried to engage every single listed HAA contractor in the Southern Ontario area to do room measurements, treatment suggestion and followup and every single one denied me. They all wanted to only handle turnkey HT setups (ie. designing & building the entire space from scratch).

I dont know if this is typical of all HAA certified contractors.

Andy K.

kromkamp

I think that is typical of most CEDIA contractors, which tend to ignore the DIY marketplace. ISF indicates if calibrations are available with installations only or if calibrator is independent. Sounds like something HAA should do as well!

www.rivesaudio.com
They have packages from basic planning for DIY up to full design & CAD work and after-install calibration/tweaking. They do not sell treatments, so they show how to DIY home build them in the sample drawings I saw. The pro-AV company I work for has signed on as a local delaer so we can use their services for commerical installations where acoustic treatment and/or sound control isolation planning are needed, but their bread and butter is 2-channel high end rooms and home theater. I was referred by Dennis since he was at the time also only doing turnkey design of the full system (that may still be the case; not sure.) Being an AV designer myself, I did not need the system wiring and site planning help, only the acoustic modeling and tweaking. If I can ever find a contractor to build out my room, I am going to become a Rives customer as well. The way it works, the local dealer has a test kit to come out and measure the room before and after. That data, along with answers about the room, aesthitcs, and system equipment is sent to Rives designers, who generate the plans for a DIYer or GC to build. Then after the room is built to plans and the treatments added, the room is measured again and any necessary tweaks are suggested.

PM me if you are in the DC area and are interested in learning more. As I said, my employer does not install home theater, but we can probably do the measurements for a Rives design sale locally.

Originally posted by mikemav
www.rivesaudio.com
They have packages from basic planning for DIY up to full design & CAD work and after-install calibration/tweaking. They do not sell treatments, so they show how to DIY home build them in the sample drawings I saw. The pro-AV company I work for has signed on as a local delaer so we can use their services for commerical installations where acoustic treatment and/or sound control isolation planning are needed, but their bread and butter is 2-channel high end rooms and home theater. I was referred by Dennis since he was at the time also only doing turnkey design of the full system (that may still be the case; not sure.) Being an AV designer myself, I did not need the system wiring and site planning help, only the acoustic modeling and tweaking. If I can ever find a contractor to build out my room, I am going to become a Rives customer as well. The way it works, the local dealer has a test kit to come out and measure the room before and after. That data, along with answers about the room, aesthitcs, and system equipment is sent to Rives designers, who generate the plans for a DIYer or GC to build. Then after the room is built to plans and the treatments added, the room is measured again and any necessary tweaks are suggested.

PM me if you are in the DC area and are interested in learning more. As I said, my employer does not install home thester, but we can probably do the measurements for a Rives design sale locally.

Any existing Rives dealer is also eligible to become an Alpha Certification Representative, if they're good enough :). We can utilize the data from their test kit as well. We analyze it using our own proprietary software, and can award certification if the room meets our strict acoustical standards. We provide a detailed 6-page acoustical report on the room, which includes early reflection analysis, reverberation times, and dialog quality including Speech Transmission Index. We do all this for $299.

In addition to analysis and certification, we also offer all the design services that Rives does. We can do very advanced acoustical analysis and modeling (including the same professional quality ray-tracing as is done for concert halls), plus complete HT design, all for very reasonable prices. Our complete custom design and acoustical evaluation packages range in price from $395 to $1595. We give you CAD plans for use by DIYers or professional builders.

Regards,
Terry

I agree. I've heard good things about Rives but for my money, I would prefer to support someone like Terry who hangs around here and gives away so much free advice.

And I probably will enlist Terry's services at some point in terms of remote analysis. However it would be nice to have local options too.

Okay, thanks for the help everyone so far. I have a few more questions that I was hoping to get some more help with.

After thinking things through, I think I will probably try to make some treatments myself to save some dough. Thanks for all the advice and links!

One problem I am having is locating a place to buy OC rigid fiberglass. Based on the info provided here, I would like to try OC 705-FRK in 1" and 2" to make different styles of treatments. I have contacted several HVAC places and no one seems to use it. The closest I have found is a place that uses EnDuraGold. It is an FRK-type board, but the accoustical properties on OC's web site are much lower than 705. Any ideas on how I can get my hands on a box or two of 705?

Second, I'm trying to find fabric. I have been to two different local fabric stores, but can't really find anything suitable. Can anyone offer suggestions of places to find good material to use to cover the treatments?

Thanks,

Jon

For fabric: http://www.silentsource.com/gom_index.html

Jon,

> One problem I am having is locating a place to buy OC rigid fiberglass. <

If you modify your User Profile to include your location it will be easier for people here to give you specific advice. That said, this place has many outlets around the US:

www.spi-co.com/servicecenterdirectory.mv

--Ethan

If I can ever find a contractor to build out my room, I am going to become a Rives customer as well.
Our Certified Home Theater Builder program will be rolling out shortly ... once a NARI member is certified by us to build acoustic spaces, dealers and home owners will be able to seek out builders that have been specifically trained to build these special purpose rooms. Starting at CEDIA EXPO, those individuals who've met the training and experience requirements can sit for the Home Theater Designer exam. The Master Designer practical exam (a two day exam) will not be "in the can" for a few more months.

Originally posted by Dennis Erskine
Our Certified Home Theater Builder program will be rolling out shortly ... once a NARI member is certified by us to build acoustic spaces, dealers and home owners will be able to seek out builders that have been specifically trained to build these special purpose rooms. Starting at CEDIA EXPO, those individuals who've met the training and experience requirements can sit for the Home Theater Designer exam. The Master Designer practical exam (a two day exam) will not be "in the can" for a few more months.
This sounds like a much-needed program for the industry. In addition to the mystery of sound isolation construction, contractors typically have no experience with stretch fabric (GOM etc.) installation. I hope you are making this a significant part of the curriculum. Track-based fabric installation is extremely important, in addition to the easier "cover the edges with trim" method that is possible for some but not all room designs.

Regards,
Terry

Dennis

Is this Design Cinema Privee certification or are you talking about CEDIA Home Theater Designer certification. Will there be a CEDIA Home Theater Installer certification (for fabric, stage, riser construction techniques)?

BTW can you PM me who to bug about updating CEU records - I sent to the generic mail on the web page with no response. Really reluctant to spend more money on training if I am not getting credited!

Originally posted by kromkamp
For what its worth, I tried to engage every single listed HAA contractor in the Southern Ontario area to do room measurements, treatment suggestion and followup and every single one denied me. They all wanted to only handle turnkey HT setups (ie. designing & building the entire space from scratch).

I dont know if this is typical of all HAA certified contractors.

Andy K.

This is fairy typical in my market as well.

IMO, there are DIYs, and then there are strokes... and DIYs are always welcome to call me.

I also specialize in turnkey HT and multi-room audio systems, but I always return calls from DIYs seeking assistance and guidance and I give everyone the benefit of the doubt. I would much rather deal with an upfront person that is honest about their intentions to do the work themselves rather than a stroke who is leading me on under the guise of getting a job bid, with every intention to sponge up some info and go e-shopping for all the gear.

With all the tremendous resources like this that allow anyone to research on their own, I feel pretty insulted when someone wants me to design their systems for them for free.

Everyone wants a fair price, and many here also want the satisfaction of building a portion of their dream system, but I get turned off by guys that lead me on... We have to make money at what we do for a living just like everyone else in the world.

I have also been known to come over and lay eyes on the project in question even if we are not able to get involved in any way because of scheduling issues, etc. If I meet someone who is building an ambitious project that wants do do a lot of it themselves, I would rather help them out if I have the time rather than snub them. Maybe I only provide a small piece of the overall project, or even nothing at all.

Who knows, someday I may get a referral from a less mechanically inclined friend of a DIY person I helped out, rather than have a snob reputation and force his friends go to the big box places and get bad advice and wind up with mediocrity.

We even hired a guy that we met as a DIY guy when he was shopping for a projector we carried. He worked for a retail a/v store, and was/is an avid enthusiast and AVS lurker. He now works for a competitor, but we have a lot of respect for him and his new employer, that's just the way it worked out.

As I said, I have been known to provide tons of advice and resources for the very low, low price of free... HT has been pretty good to me over the years, and I don't mind spending some spare time speaking with enthusiasts or contributing at places like this.

Andy,
I am in the Chicago area, but I will likely be visiting Toronto the first weekend in June to take the CEDIA Designer I exam I have been putting off. If you are interested at all, I could bring my laptop and mics with me and stop over. PM me if you are interested in discussing this.

Originally posted by Dennis Erskine
Our Certified Home Theater Builder program will be rolling out shortly ... once a NARI member is certified by us to build acoustic spaces, dealers and home owners will be able to seek out builders that have been specifically trained to build these special purpose rooms.
Are you speaking of NARI remodeling contractors??

This is a good idea, but the dealers we deal with every day sure are hesitant to listen to us "audio guys" when it comes to building methods.

What has your experience been with relaying advice/recommendations to builders and actually having them follow it??
In the time I take explaining WHY I want linear diffusors and staggered stud walls with USG acoustic sealant applied to the sole plate/wallboard seams to the manufacturer's specs, I could probably construct the rooms myself.

The electricians are cool with us, and when we specify dedicated circuits, specific light fixtures, home run wiring for Grafik Eye or HWI panels, etc. they understand that there are legit reasons.

On the other hand, the builders think we are nuts, and that the isolation/noise control methods we advocate are overkill, and that we are simply blowing the clients' budget.

Starting at CEDIA EXPO, those individuals who've met the training and experience requirements can sit for the Home Theater Designer exam. The Master Designer practical exam (a two day exam) will not be "in the can" for a few more months.
I hope you are not planning to actively invite builders to come to CEDIA, the old timer integrators will lynch you. As an integrator who has been a member of CEDIA since the early days, I do not want the suppliers that display on the floor to mistakenly solicit builders standing before them at a TRADE show when they are not a part of our trade.

I am interested in acquiring the Home Theater Designer Certification and/or Designer II Cert. as soon as they are available. Do you expect DII to be available by Expo??

Thanks,
Rick

Kras.... contact Scott McCormack at CEDIA.

The Home Theater Designer and Master Designer are CEDIA certifications and will be challenges.

The Home Theater Builder will not be a CEDIA course but rather one I am working on outside of CEDIA.

The Home Theater Designer Exam will be ready by Expo and those with Designer Certification will be provided the announcement in advance of CEDIA. The Exam is rigorous and will require a broad base of knowledge to pass. The Master exam will not be ready this year and is a practical exam (which is why it is taking soooo long to prepare).

Yes, NARI is the remodelers organization. In general, we've found builders to be receptive and by and large follow our direction EXCEPT ...
The exception has been home builders that build on spec. They, as a general group, once they find out what needs to be done, don't care to do so since the additional expense is not part of their original budget and they have no certainty the future homeowner would even want such a room. But, where a homeowner is involved and willing to pay for the additional expense, they are all ears.

We have had a couple of cases where the builder didn't follow our instructions and took shortcuts (without consulting us or the client). In those two cases, the builder (at the builder's expense) had to rip out the work and start over.

Good morning Dennis!!

Sorry I was editing my post as you posted...

Thanks for the reply, and I am relieved to hear that the builders' spec is outside of our trade organization.

Best of luck with this, and if you need any more participants to provide field perspective to the process, I am rarely at a loss for words and would be happy to contribute. Feel free to PM me to discuss.

I had to pull a Sony 400 disc changer recently and replace it with a Pioneer 300 disc just to save a couple inches of depth in a whole house music rack on a modest job where the client didn't want to give up a closet for us.

I gave the GC and the lead carpenter of a CUSTOM builder that we work for a rack tools drawing of the AXS rack that was going to be used with very large type o the measurements... but they did not accommadate me on the dimension change.

Funny thing is, the HVAC guy ran my ventilation run to basement, but opened one of my holes to do it!! I had to move aside insulation and drill a new one in my dress clothes standing on borrowed ladder the day the rockers were there to cover it!!

The reply from the other carpenter regarding the cabinet was that the change orders have to come from the client, not the other subs. It was like a bratty little child saying "you're not my boss, I don't have to listen to you".
It was all I could muster to keep from stuffing him in that cabinet.

I had to switch to a Slim5, lace the wiring on the INSIDE of the rear rails, build and test the rack on a piece of carpet, then lift it and slide it by hand into the cavity shoving it ALL the way against the rear of the carcass and secure it through the bottom blanks w/ a right angle drill/driver.

That will be a service nightmare is anything ever needs attention.

As a pro, I am excited to see THX, CEDIA, and others taking an active role in promoting acoustics in the advanced Certifications.

I have heard that someone at this year's Expo will feature two identically sized rooms with idential equipment, except the one will be acoustically treated with advanced methods and products to compare to the other totally untreated room.

Dennis, Terry?? Either of you involved in this of have any additional info about this??

I am involved with this as part of the Acoustics Guild.

Thanks Dennis!

I see Theo K. has retired from CEDIA Architecture award participations and is now sponsoring the award. Maybe a HAA/ISF award for best Technical Theater? I hate cringing when I see the awards catalog! Or maybe a Home Theater Designer award once there is a large enough pool of designers - say they have to submit a certification checklist sheet for the theater.

Originally posted by krasmuzik

...
Or maybe a Home Theater Designer award once there is a large enough pool of designers - say they have to submit a certification checklist sheet for the theater.
Better yet, measured and certified acoustical performance data!

Regards,
Terry

Originally posted by krasmuzik
I hate cringing when I see the awards catalog!
Oh man... I just got the notice that we missed the deadline for "best dressed" competition. My partner is super anal about dressing the racks, and we always joke that the top 2 or 3 awards are actually nice, but it tapers off REALLY fast which leads us to believe that not too many people submit.

Or maybe a Home Theater Designer award once there is a large enough pool of designers
This is a great idea.
I am concerned at how practical this would be. It would likely be a salesmanship/machismo contest unless the details of the client meetings, builder meetings, and designer/decorator meetings are outlined with can and cannot requests and idiosycratic requests from homeowners. The totals would need to be offset somehow to compensate an interference factor.

I'm not a bad designer because a client insists on a screen that is too small because they want the front pillars HERE, flimsy sconce bezels that buzz from LF, or chairs that have super tall back cushions... I do what I can to educate the clients on more appropriate choices to right the wrongs, but ultimately I am just doing what they want a lot of the time.

cinemascope,

But I bet Theo and Russ get their way what with their $$$$$ retainers just to decide if they want to take the $$$$$$$ job or not!

I think awards like that should be based on ultimate performance - if it was checklist or metric based - you could get dinged for the high backed chairs. But if that was the only thing wrong compared to the competition that year - maybe you could win.

Still would beat the other stuff in the "spent a ton of money for a lousy sounding washed out video room" categories. Also I bet the high end customer given a target of - "Do you want to be award winning?" would be more likely to give in.

Why do you think Terry is doing his Alpha certification that exceeds THX specs?

Originally posted by Toeside
Question regarding OC703 on my front wall.

My plans include covering the front wall with OC703. I'll have a false wall about 30" out from that covered in black GOM FR701 fabric. My L/C/R speakers and my sub will be behind this false wall. My RPTV will be recessed into this false wall.

Should I cover the OC 703 on the wall to keep the fiberglass from possibly becoming airbourne inside this false wall area? I've never seen OC703, so I don't know if this is a valid concern or not.

I know someone piped in to say that these types of panels rarely "shed" any fibers, but I wanted to re-open this and say that there are specifications for shedding, although they have a different term that escapes me at the moment.

You may still want to cover the panels, because if any portion is guilty of losing fibers, it is the rough cut ends. In place of the pricy GOM in this low visibility application, you can go econo and seek out some upholstery fabric locally that has a similar ANSI/ASTM rating for fire retardancy as the GOM.

Also, the areas where you are using the panels is not entirely important from the perspective of high velocity air hitting the panels. Ductboard is made from the same material, and in a very similar manner to OC-703 panels. These materials are used to construct or line duct runs to achieve serious reductions in noise transmission through the dusctwork without causing issues from airborne fibers.

Since these products have a proven track record of maintaining their integrity when faced with the high velocities inside air ducts, you can rest easy that your panels behind a false wall will not be contributing to the "itch" factor, regardless of the proximity to the HVAC vents..

The only time you have the possibility of itching is when you are cutting and trimming the panels for size, electrical boxes, etc.

I prefer to do this outside or in a garage and immediately shop-vac everything to keep the fibers from being tracked into the house, and most importantly, off of my skin.

Companies like Kinetics that custom fabricate these panels on a production level use a chemical hardening procedure on the all ends that ensures that the ends will not fray or lose fibers, and also the performance ratings of the panels is actually different with the hardened ends.

Also, their mitering, custom radius shaping and upholstery abilities far outweigh my own, I have never been dissapointed in the fit and finish.

...there is a move afoot, BTW, to have independent audio/video measurements made in rooms submitted to CEDIA for design competitions at EXPO. Several different methods have been discussed but I'll leave it at that for now.

Wow.

By "independant" you mean a select group of accredited individuals that maintain calibrated mics/systems of particular requirements??

I would get involved a program like that from both sides, submitting rooms as well as independantly measure/verify/certify rooms for other companies for the Expo contests.

Yes...the measurement would be either by:

1. a non-related competent and trained individual using approved devices; or,
2. a device would be shipped to the site, plugged into the system, run an established scenario capturing the data that would be sent back for analysis (audio and video).

The dealer submitting the room would bear a cost for the testing. Obviously, there's alot of holes which is what we're working through. However, in plan (1) above, the individual doing the measurement would never be allowed to submit his/her own project to avoid any direct or indirect conflicts of interest.

I'm building a cabinet to house my center channel speaker and form the base of my screen wall. The cabinet has to be movable for access to the screen wall, so it is built of 3/4" ply and 5.2mm ply front with medium bracing. Approx size is 8' wide 2' high and avg. 1' deep with a bowed front. Finished weight will be about 60 lbs.

My question is this: the cabinet has several unused (unopenable) airspaces in it: 2 are approx 7400 cubic inches and one is 5040 cubic inches. I was planning on stuffing these with fiberglass insulation batts. I want to avoid the cabinet resonating. Should I leave the compartments sealed, or add air ports? If so, is there any way to calculate the area of the ports? Can these chambers be used to serve a useful purpose beyond being acoustically inert (I.E. serving as bass traps)?

Thanks in advance for any advice given, I'm already deeply indebted to this forum!

Although I have included some ideas, I might just skip the idea of creating an trap/absorber from this and laminate a few layers of thin ply together to make a thick and rigid front and then wrap that in curved pieces of acoustic treatment or a perhaps a matching piece of carpet up to the proscenium apron/stage.

Your medium bracing remark is a little vague, but that panel material is not very rigid on it's own. Because that front panel is not likely to be very rigid as it is, it will likely behave like a diaphramatic absorber, but the range and level of absorption will be a little bit difficult without physical testing because of the additional rigidity provided by the curve will make it behave differently than a flat piece of stock of those same dimensions.

Since the front panel will be less than 1/4" material, you may have been able to turn it into a panel trap, but since it's bowed it will have additional rigidity and behave like a thicker panel. Maybe Terry, Dennis or Ethan can shed further light on what can be done.

Perhaps you could use a thinner material or create an open frame that can be wrapped in a more acoustically transparent material like GOM and then tradtional traps could be placed within the cavities to wither side of the center channel cavity.

Either way, I would definitely seperate the cavity for the size of the speaker and stuff that speaker cavity with something very absorptive, not to treat the room, but to minimize the cave like resonance of having a speaker in a cavity like that.

If you decide to skip the traps in the stage plan, the side cavities should be filled with someting inert so that tey do not add to the resonances you will be dealing with.

Many posters here prefer sand in the stage cavities. But since you mentioned moving them, perhaps stuffing the heck out them with unfaced acoustic batts would be a better choice.

Are you planning to have the speaker protruding from the face of this stage to clear the stage/apron lip?? or are you flush mounting it and making grille cloth cover to match the cloth/carpet on the face??

Thanks for the detailed response. I will attempt to attach a sketch of the cabinet. Since it is mostly constructed, I am reluctant to make major changes in the design. The front will be thin, but fairly rigid. I intend to paint the cabinet to integrate it with the doors and other millwork in the room. The center channel speaker has its own compartment, which is only slightly larger than the speaker itself (about 3/4" all around) and is open at the front and back, so that the grill of the speaker is visible, but flush with the cabinet front (Vienna acoustics maestro FWIW). The "hollow" 3 compartments (which I intended to stuff with insulation) are in addition to the speaker compartment. The main option still open to me is whether to seal these chambers, or provide opening ports (on the back of the cabinet), and if so, how large?

Originally posted by cinemascope
You may still want to cover the panels, because if any portion is guilty of losing fibers, it is the rough cut ends. In place of the pricy GOM in this low visibility application, you can go econo and seek out some upholstery fabric locally that has a similar ANSI/ASTM rating for fire retardancy as the GOM.

Also, the areas where you are using the panels is not entirely important from the perspective of high velocity air hitting the panels. Ductboard is made from the same material, and in a very similar manner to OC-703 panels. These materials are used to construct or line duct runs to achieve serious reductions in noise transmission through the dusctwork without causing issues from airborne fibers.

Since these products have a proven track record of maintaining their integrity when faced with the high velocities inside air ducts, you can rest easy that your panels behind a false wall will not be contributing to the "itch" factor, regardless of the proximity to the HVAC vents.

I know I am quoting my own previous post, but I just wanted to throw this on to the sticky for all eternity.

This product from Johns Manville...
http://www.jmairhandling.com/pdf/AHS-202.pdf
...can be used to seal off the cut ends of any fiberglass sheet panels that are DIY or cut open for any reason.

The major reason is to give the panels a more sealed egde for durabilty, to prevent fraying and denting. This is especially importent for outside corners on walls, soffets, hish boxes, etc, where the edges can be dented or begin to fray with repeated contact.

A side benefit is that this is the equivelant user applied product to the solution that is factory applied to the airstream surfaces and edges of the JM duct liner material.

If ultimate peace of mind regarding shedding or fraying is an issue, you may choose to cover your panels with this product, or just choose a duct liner product to begin with.

The absorptive characteristics are different and I would count on significantly less HF absorption, but all of the specs are published so you can compare the various products and decide your plan of attack.

Scopes,

> Since the front panel will be less than 1/4" material, you may have been able to turn it into a panel trap, but since it's bowed it will have additional rigidity and behave like a thicker panel. <

Yes, exactly.

So in this case Sam should make the front as open as possible and pack the entire cavity tightly with fluffy fiberglass. If the entire front is open and covered with grill cloth or whatever, that will give the most bass trapping. Especially if the cavity is close to the ceiling at the wall-ceiling corner (or near the floor at the wall-floor corner).

--Ethan

Is it essential that the "open" side be the front, I.E facing the room? The cabinet will be a few inches from the wall behind it. Would it be possible to cover the back with grill cloth instead? I was under the impression that the low frequency sound waves targeted were not very directional. Thanks!

Sam,

> Is it essential that the "open" side be the front <

Probably, but I have no way to know for sure. Bass waves are considered omnidirectional, but 1) that describes mainly the ears sensitivity to their source direction, and 2) the waves still have to be able to find their way into the absorbing material.

--Ethan

I have some nasty echos in my family room which houses my home theater system. Hardwood floors, lots of glass (30%) and relatively bare walls. My wife has agreed to covering some of the bare walls with sound absorbing materials if that in turn can be covered with wallpaper. GOM or fabric may not be acceptable.

The room is 18x30 with 14ft angled ceiling. The rear of the room is open to the kitchen (18x15) and a hallway to the rest of the house.

The wallpaper is not extremely hard, but definitely stiff (but thin). I am considering covering areas with a .25" to .5" materials, some of which are recommended in this thread. My questions are as follows:

1) Will the wallpaper surface defeat the purpose here and be reflective?
2) Must I use instead a more absorbant fabric (GOM?) over the panels?
3) Is .25" or .5" enough to kill the echo and give a relatively damp room? I could do about 35% of the wall area with it if needed.
4) Should I just cover the maximum amount of wall area I can with .5", wallpaper it and hope for the best?

Thanks very much.

Originally posted by DennyL
I have some nasty echos in my family room which houses my home theater system. Hardwood floors, lots of glass (30%) and relatively bare walls. My wife has agreed to covering some of the bare walls with sound absorbing materials if that in turn can be covered with wallpaper. GOM or fabric may not be acceptable.

The room is 18x30 with 14ft angled ceiling. The rear of the room is open to the kitchen (18x15) and a hallway to the rest of the house.

The wallpaper is not extremely hard, but definitely stiff (but thin). I am considering covering areas with a .25" to .5" materials, some of which are recommended in this thread. My questions are as follows:

1) Will the wallpaper surface defeat the purpose here and be reflective?
2) Must I use instead a more absorbant fabric (GOM?) over the panels?

The paper isn't the issue as much as the adhesive that soaks into it and dries stiff which makes that paper so crispy. If you havce ever removed old paper without a steamer or the release agent, you understand the term.

I have seen some wonderful papers based on softer materials that look tremendous. It's just that they get stiff as a board when the adhesive soaks into the back layer of paper.

Some of the finest homes I have ever been in had expensive fine fabric with a wallpaper style pattern strecthed over the walls and suspended just off the wall surface. I don't know what this method is called, but then again I don't subscribe to Architectural Digest...
There was a little bit of deflection to another wall substrate if you pressed your finger against it. Something like this would allow you to use a thin duct liner of fiber panel material in the trouble spots determined by the mirror method or a ray trace.

This may be a better solution if you can give up a little more space and fit it into your budget.


3) Is .25" or .5" enough to kill the echo and give a relatively damp room? I could do about 35% of the wall area with it if needed.
4) Should I just cover the maximum amount of wall area I can with .5", wallpaper it and hope for the best?

Thanks very much. [/B]
.5" is better than .25", and .25" is better than nothing...
I am still not sure that fiber panels are the best solution for your application.
Even if the stiff paper didn't reflect, I doubt it would bond well to fiber panels.

If you research the stretched fabric method and it is not your wife's cup of tea, or it is a budget breaker, another option to look into is a skimcoat of acoustical plastering.

Nearly any plaster contractor in the phone book has availiability to acoustical plaster and understands it's application.

The absorption characteristics, and therefore the results, are based on variables like how thicky it is applied, etc. and an acoustician would generally specify these variables for it's use.

To read more for yourself, go here:
http://www.usg.com/navigate.do?resource=/USG_Marketing_Content/usg.com/web_files/products/prod_details/USG_Acoustical_Plaster_Finish.htm

Another choice is a new system from Switzerland called BASWAphon that RPG offers in the US.

Famous acoustical guru John Storyk used this system on a This Old House project, and you can read about that here.
http://www.thisoldhouse.com/toh/knowhow/interiors/article/0,16417,216779,00.html

Read the section of the article called "Mid- to High-Frequency Reflection Control" where he descibes a new product he used in that room.

As I said, RPG distributes this material, and you can read more info here:
http://www.rpginc.com/products/baswaphon/

I am not positive if you can paper over this.
I'm thinking you cannot, because you actually don't even paint it.

You tint the plaster material before it is troweled and skimmed.

I would send out a letter to RPG to confirm.

Either this new material, or the skimcoat method with traditional acoustical plaster to a lesser extent, can help make a room less "live" yet still retain the traditional aesthetic apperance.

Either method should allow your wife to paper the space, but as I said, double check with the manufacturer of the panels before you order them.

If you want the best results (and some quality entertainment) call in a acoustician and an interior designer and let them battle it out.
Right now you and your wife are having that debate on a smaller scale, when it's two pros that are each dead set against each other's plans and both very good at what they do, it's not pretty...

Any words of wisdom for non-standard rooms?

All the advice in this thread seems to assume a basic rectangle / shoebox / golden ratio room. What about sloping ceilings/walls on both sides? Basically a barn like room that many people get when they finish off attic space. Also, how about half walls that form ear level and below U shaped squares in the back of the room. Or hallways / stairwells leading into the room?

Any words of wisdom for non-standard rooms?

All the advice in this thread seems to assume a basic rectangle / shoebox / golden ratio room. What about sloping ceilings/walls on both sides? Basically a barn like room that many people get when they finish off attic space. Also, how about half walls that form ear level and below U shaped squares in the back of the room. Or hallways / stairwells leading into the room?
Such rooms can make excellent theaters. Acoustical modeling and prediction isn't straightforward, however. Ray-tracing will model a room well at most frequencies. But it doesn't perform well at the lowest frequencies, so it won't tell you much about room modes. The Finite Element Method (FEM) is the technique of choice for analyzing modes in odd-shaped rooms. We do pre-construction HT analysis at reasonable prices, and have capabilities to do both professional ray-tracing and FEM. If interested, PM me.

Regards,
Terry

Every room is different. We'd need more information and specifics like sizes, seating locations, speaker locations, how many people, usage, etc. before being able to give even a basic recommendation.

That said, the basics are pretty much the same. Kill the front wall, kill the reflection points, address the reverb time in the room appropriately throughout the spectrum, etc. How much, what kind, and where will depend on the answers to the specifics.

I want to treat my dedicated theater for absorbtion at first reflection points. My first question is: (1) What are the pros / cons of attaching OC 703 / 705 / or equivalent (covered in acoustically transparent fabric) directly to the drywall rather than in wood framed panels? If attached directly to the drywall, am I really helping any or just spending money?

My second question pertains to sound insulation (i.e., keeping outside of the theater sounds out, and inside the theater sounds in). My construction is double 2x4 walls with a 1/4 inch air gap between the 2 walls. The outer wall will be filled with 3 1/2 inches of expanding polyicynene foam (the spray in stuff that expands 120x). The inner wall I intend to fill with fiberglass batts.

(2) For the fiberglass batts, does it matter if they are faced or unfaced, and if faced, whether the face "faces" in or out? And does the foam or fiberglass in the wall provide any acoustic benefit?

Thanks

First for the isolation... IMO the expanding foam does little or nothing to assist in isolation as I believe most of them are closed cell foams. You'd be better off with standard fiberglass and a barrier on the outside of the outer wall.

For the absorbtion inside the room... You can certainly be effective mounting 703 directly on the wall - provided it is thick enough to do what you need done. 2" of 703 framed 2" out from the wall will reach deeper than 2" directly on the wall but not as deep or as tight as 4" directly on the wall. Also, the 4" and the 2" spaced off the wall will do no more from say 1kHz up than the 2" mounted to the wall. What changes is how far down they're effective and at what level of effectiveness.

As for facing, again it depends on what you need. Usually one uses unfaced. However, if you only want bass/low mids absorbtion, you can certainly use FRK with the facing out into the room.

The insulation inside the wall keeps it from ringing and assists the drywall over stud construction to act like a broadband resonant panel trap that is pretty effective from say 100Hz through around 250Hz+.

Bpape - Thanks for the info.

Next: Is there a material that can be used in place of gypsum drywall (i.e., paintable, firm, etc.) but has the characteristics of rigid fiberglass with respect to absorbtion? If so, wouldn't that be a good solution for walls and ceiling? That way, all surfaces are built in bass traps, then, to prevent room from being too dead, reflectors / diffusors could be added as needed. Benefit would be that a diffuser / reflector doesn't need to be inches deep.

Most expanding foam insulation in the wall is worse than having nothing in the wall. It's rigid and closed cell and conducts sound. It's a good thermal insulator, but worse than useless for acoustics and sound proofing.
'Expanding polyicynene' you mention may be Icynene, which is an open cell foam with absorbtion (http://www.bobgolds.com/AbsorptionCoefficients.htm), in which case it's fine. Less absorbtion than some other products, but probably better air tight seal. Search for Icynene at AVS and you'll find someone who's had it installed.

If you can avoid faced fiberglass, it's probably better. But if you must use faced, I believe the recommendation is to put the facing against the drywall rather than into the gap, both because that has acoustic benefits, as well as it's the way it's designed to be installed. There may be vapor barior issues. Lightly filling the entire cavity (no airgap) with insulation may have firestopping benefits.

Attaching the absorber directly to the wall is fine. Impailing clips may be what you want to attach it with. Spacing it out from the wall gives you more absorbtion at lower frequencies for free, which may be a good or bad thing depending on what other absorbtion you have in your room (e.g. 20 leather seats).

The job of gypsum/drywall is to be cheap and reflective and firesafe, i.e to use it's mass and reflectivity to keep the sound energy in the room, rather than letting it out of the room. Similarly to keep the sound energy outside of the room out, to lower the noise floor and thus increase the dynamic range of the HT. If you're into soundproofing, don't think of it as an absorber, and don't try to make it into an absorber.

Thanks. It is icynene foam. I'll do the search for icynene & see what the avs experience / expertise is.

Greg

There are two types of polyicynene spray in foams, high density and low density.

The high density variety is the closed cell product that the fellows are warning you to avoid. It makes a very rigid wall system that will transfer noise through with little loss.

This type of foam is generally used below grade where moisture is a concern.
Remodelers love to use it against stacked stone and block foundations because it expands into every crack and crevice and has enough structural holding power to bond the wall together and help keep the foundation from future disentegration.
In addition, it is an absolute moisture barrier for these notoriously leaky foundations.

Low density, or open cell polyicynene foam insulation is a great product to use in your application, but in the outer most portion of the double wall. It has similar vapor barrier characteristics of the closed cell products, but it will not trap moisture. (no mold)
It is generally specified for use above grade.
http://www.icynene.com is the major player in open cell.

Faces in or out on batts has to do with vapor barrier, and this varies by your location.
Gulf coast areas need the barrier out, or more likely they will use an external barrier and unfaced batts. The rest of the country requires it to be on the inner most section of the cavity.

If none of these walls is an exterior wall, use unfaced batts. If one or more walls are exterior, use the open cell spray, or consult the insulation contractor or building inspector to make sure your walls will meet any code requirements.

Nothing will slow down a project faster than having to re-do an expensive part of the project that you have done incorrectly. It's worth getting right the first time, air quality concerns are high on everyone's list when selling/buying a home, and mold remediation is EXPENSIVE.

In the wall closest to the room, I would recommend acoustic fiberglass batts. I like the Johns Manville batts because they perform well and are also formaldehyde-free.

It sounds like you have a nice project going, you should create a thread and post photos and updates as to the progress.

Best of luck.
--Rick

Rick - thanks for the help. I agree that getting it right the first time costs a lot less than changes later. I'm trying to do everything possible to get it right! In fact, I made the a/c people come out today and replace the existing "boots" on the end of the ducts with oversized boots, so that the conditioned air as it enters the room will be slowed down somewhat.

Is creating a thread for one's own room pictures ok? Not sure of the protocal and whether that is something ya'll do and is in good "form" or whether that is "bad form," etc. If it's "proper", I'd be pleased to share my labor of love (or maybe lust is a better word when talking about a home theater!) with all of you!


Greg

I personally did use closed-cell foam in my basement HT, and I'll tell you why.

I'm firmly convinced that the BSC method of insulating basement walls is the correct way to go. This method employs no vapor barrier but instead a vapor retarder, to allow moisture to dry to the interior at a slow, controlled rate (since it cannot dry to the exterior below-grade).

Closed cell foam of approx. 1" is a vapor retarder (perm ~1.4). Open cell foam is not (perm ~15). I've also heard a lot of bad things about open cell foam - the expansion rate is so great that there are often huge (ie. inches wide) air bubbles in the foam that severely compromise the R-rating.

Yes, this may mean I have compromised sound attenuation. IMO the fact that they are foundation walls (ie. only consideration is flanking noise) and the fact that double-drywall w/ damping is going to do 100X more than 3.5" of fiberglass ever would just isnt worth the tradeoff of possible mold issues. Yes lots of homes dont face mold but lots do. If you consider all those older homes that have a 'musty basement', thats a mold issue.

Just my 2 cents.

Andy K.

I have a friend with a set-up that is on the bright side. (Klipsch 7.1 with a Yamaha 2500 receiver)
Originally, his room was horrible. His system was in an 18X23 drywalled room with 9 foot ceilings and a ceramic tiled floor. :( It was an echo chamber.
He has since put in two large, thick rugs and hung some dense curtains all the way across the front of the room. (Helped a ton) Now that he has seen these improvements, he wants more.
He now wants to tone down the brightness of his set-up.
He really does not want to put up GOM if he does not have to, but would if there are no alternatives.
I told him he should treat the room (Knauf/batting/GOM) and be done with it.
It is probably what he will end up doing anyways.
Is there a way to reduce brightness in a room with out going all out with treatments.
And, if he does treat the room, will his speakers not sound as bright?

Craig

Treating the room will not change the frequency response that the speakers yield. What it can do is to tame the reflections and bring the reverb time more under control.

However, treating only the mid/top of the spectrum is not a good idea. The whole spectrum should be addressed.

As for covering, you can use Muslin dyed to the color of his choice - for treatments this will work just fine. You can get lightweight muslin at JoAnn Fabrics for < $15 for a whole bolt. Use the money saved to purchase the appropriate materials to address the bass in the room.

Treating the room will not change the frequency response that the speakers yield. What it can do is to tame the reflections and bring the reverb time more under control.

However, treating only the mid/top of the spectrum is not a good idea. The whole spectrum should be addressed.

As for covering, you can use Muslin dyed to the color of his choice - for treatments this will work just fine. You can get lightweight muslin at JoAnn Fabrics for < $15 for a whole bolt. Use the money saved to purchase the appropriate materials to address the bass in the room.

Thanks bpape,

I will show him this post... except the part I called his room an echo chamber. :D
I think he is seriously considering using wall treatments.
He is not a real audiophile and at least for now I think he is going to live with what he has.
He wants to see what my theater sounds like when I am finished with mine before he undertakes it though.
Next, I have to get him to paint his white walls and ceiling a dark color. :rolleyes:
If anyone has more to add on this please feel free to chime in. :) :)

Craig

Hi all, great thread - I finally made it through! I'd like to post some questions and get expert feedback.

Building a dedicated theater room in the basement of my new home. The room will be 16' x 24' with two levels of riser. Top level will have concession stand, equipment rack, maybe a popcorn machine, etc. 2 theater seats centered on it, room permitting. Next level, row of 4 reclining theater seats. Floor level, another row of 4 theater seats. When they frame it I'm going to just have them mud, tape and prime the front wall but not texture it, and that will be my screen, after I've Goo'd it and trimmed it. 7 speakers in the ceiling (I was thinking of the Russound series of ceiling speakers that you can aim so the sound goes in the right direction instead of straight down).

So, for acoustic treatments, I was reading from this article (http://hometoys.com/htinews/jun05/articles/kinetics/totalroom2.htm) which maintains it's acceptable to keep some of your painted drywall as reflective surface and put up panels in the hot spots. I was thinking of building shaped panels like in their models and putting them in the primary reflective areas as discovered using the mirror test. I would also put bass traps in each corner like the ones described here (http://www.diynetwork.com/diy/hi_family_room/article/0,2037,DIY_13912_3471072,00.html). There will be thick carpet and I'll also put panels on either side of the screen, and perhaps a bookshelf along the back wall to diffuse some of the sound without deadening.

Do you think this would work well? The room doesn't have to be perfectly tuned but I'd like it to be nicely acoustic with not too much echo.

Also, does the subwoofer have to be in the front? I was going to put it next to my equipment rack in the back.

And how thick do those panels have to be? I think anything more than 4" would stick out like a sore thumb.

Thanks for your advice!

Equus

Yes. That plan will work fine. The trick is getting not only panels in the right places, but getting the right balance of materials so you're dealing with the enitre spectrum equally from a decay time standpoint.

The thickness of the panels will be determined by what the room needs and what the specific application of each panel is.

As for speakers, at a minimum, get speakers that fire toward the audience for the front 3. If you must do in-ceilings for the rest, at least that's not as bad. If you put in-ceilings in the front, you'll have absolutely no shot at locking the sound to the image and you won't get anything in the way of an aural image. Check out some other companies. If you're budget challenged, there are still other companies that make reasonably priced ceiling and/or in-wall speakers that will do a lot better than the Russounds.

Good luck.

Hi bpape:

Thanks for your response. I know in-ceilings are generally not good for imaging, but I was "told" these Russound speakers (http://www.russound.com/sph6tt.htm) with their aimability would work well. Do you think that's not the case? If so, do you then have better suggestion in the same price range? I don't think I'm going to have much room over the top of the screen for the center-channel speaker, as I'm going to try to make the screen height almost the entire 10' floor-to-ceiling distance. That's what got me looking at in-ceilings in the first place.

And do you think it's OK to put the subwoofer in the back? Or is that a bad idea? I forgot to mention that each of the seats also has a "buttshaker" sub in them as well.

Equus

First, you need to see what your room, your seating distances, and your PJ will support in terms of picture size. Bigger is not always better. On top of that, if your screen is almost to the ceiling, you're probably going to be pretty uncomfortable watching movies with it up that high. Usually, you want your eye level about 1/3 up on the screen.

If you can't put the center above, then do it below. No. I don't think ANY in ceiling speaker is going to do a good job across the front. You really need to lock the sound to the image. The movable tweeters are OK but the rest is still firing straight down and that extreme off axis response is not going to be even close to flat across multiple seating positions.

You might want to put this in the normal area of home theater construction. It really doesn't belong in the acoustics thread.

Well bpape my main questions were of acoustic panels and bass traps, so I though appropriate to this forum. I'll look into what you said about ceiling speakers and screen size. Thanks for the advice.

Equusz

My room is 22x14x8. I am looking at bass trapping and first reflection sidewall treatments as a staring point. My thought on corner bass traps: floor to ceiling OC 705 two foot hypotenuse with no airspace behind – basically fill the entire corner out to two feet. My grade school math is a little rusty but my calcs make it: 2’ hypotenuse = 1.4142 feet out on each side wall = 1 square foot = 1 cubic foot per vertical foot x 8’ = 8 cubic feet per corner. I can only do 3 corners because a door is in one corner – I could put 1 cubic foot above the door. That’s 25 cubic feet and that’s before any first reflection point treatment. My questions: is 25 cubic feet of 705 as a starting point too much? I know that different frequencies are absorbed at different rates, but I have no idea what this will do to the sound of a room that size – any opinions? Also: to FRK or not FRK? My plan was to cut triangles of 705 and stack them – that puts the FRK (if any) as a horizontal sandwich.

usualsuspects :

Studiotips Super Chunk including 24" and 34" cut pattern (http://forum.studiotips.com/viewtopic.php?t=535)
Harder's super chunk (http://www.bobgolds.com/TrapHarder/home.htm)
48" cut pattern (http://www.bobgolds.com/CornerTrapCut.GIF)

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

I can only do 3 corners because a door is in one cornerLeft/Right symmitry is a good thing. Consider 2 corners.

Just say no to FRK.

That’s 25 cubic feet and that’s before any first reflection point treatment.Yes, but two corner chunks, even floor to ceiling, are not very much surface area. As you'll likely have modes down to 25hz or so, broadband traps effective down to bass are a good thing -- big traps are probably fine. Consider wall/ceiling corners (overhead like soffits).

Hi - If I want to do some sound deadening between rooms (not theater, just other rooms like bedrooms and bathrooms) and plan to use fiberglass battes between the 2x4 wood studs, am I better off with 3 1/2" batts (those that are designed for thermal insulation between 2x4 studs), OR going with a 5 1/2" thick thermal batte, and "squishing it in" between the sheet rock (probably not good for thermal insulation, but possibly better for killing sound transmission)?

I'm not interested in double sheet rock, green glue, quiet rock, RC, staggered stud, etc., etc., etc. Just what is the best thickness of fiberglass batte to use in a 2x4 interior stud cavity for reducing sound transmission.

Any ideas?

Thanks.

Greg

For that application, the more the better.

Westshores,

You may want to check with your friendly HVAC guy before throwing that kind of insulation between interior walls. Unless you have air returns in each room, you may be causing some issues with your air flow and temperature regulation... just a thought.

Hi Guys,

I'm toying around with the idea of using acoustical ceiling tile to cover the walls of my theater (velcroed onto the walls - floor to ceiling - either wrapped in fabric or painted). These acoustic panels have a Noise Reduction Coefficient (NRC) of .55 up to .90. Can some of you sound experts help explain what this would do to the acoustics in the room? Also, are the acoustical properties of these panels affected if you paint them? The panels are 5/8 of an inch wide... which is good, because I don't have any inches to spare in the width of the room. Please help...

Hi Guys,

I'm toying around with the idea of using acoustical ceiling tile to cover the walls of my theater (velcroed onto the walls - floor to ceiling - either wrapped in fabric or painted). These acoustic panels have a Noise Reduction Coefficient (NRC) of .55 up to .90. Can some of you sound experts help explain what this would do to the acoustics in the room? Also, are the acoustical properties of these panels affected if you paint them? The panels are 5/8 of an inch wide... which is good, because I don't have any inches to spare in the width of the room. Please help...

I think it was mentioned earlier in this thread that ceiling tiles are too rigid and not as effective at the necessary frequency ranges. The fiberglass materials mentioned in this thread are a better option.

Do you know of any fiberglass panels that are approximately 1/2 inch wide that would help?

Also, I'm not sure I understand what rigidity would have to do with sound absorption...

Do you know of any fiberglass panels that are approximately 1/2 inch wide that would help?

Also, I'm not sure I understand what rigidity would have to do with sound absorption...
Hi Todd,

1/2" thickness is usually too thin to extend down enough into the bass frequencies. There is actually an acoustical tile which works very well. This is Armstrong OPTIMA Open Plan, but it is 1" thick and fiberglass. :)

Rigidity doesn't effect sound absorption, but fiberglass density does. The best fiberglass for HT sound absorption ranges from around 2.5 pcf to 6 pcf.

Regards,
Terry

Hi Terry and thanks for the info...

Would an acoustic tile treatment on the walls and ceiling using a 1/2 inch acoustic tile (like the Armstrong Pebble - .70 NRC) combined with bass traps in the front corners of the room work OK? Would putting the Optima Open Plan everywhere be OK, or would it be over kill?

Also, does it affect the acoustic performance of these tiles if they are painted?

Hi Terry and thanks for the info...

Would an acoustic tile treatment on the walls and ceiling using a 1/2 inch acoustic tile (like the Armstrong Pebble - .70 NRC) combined with bass traps in the front corners of the room work OK?

I think you may be likely to end up with a reverberant "hump" in the middle frequencies, where neither the tiles nor the bass traps give sufficient coverage. And the NRC of 0.70 for Armstrong Pebble is for E-400 mounting, which has a 400 mm air space in back of the tiles. Your mid to low frequency absorption will be nowhere near the E-400 mounting specs when the tiles are mounted right against a wall (A mounting).

Would putting the Optima Open Plan everywhere be OK, or would it be over kill?

Everywhere may overkill, depending upon your room. But if you use these tiles, you could also just go with 1" fiberglass. The only advantage to the tiles is that they have a finished surface, which doesn't need fabric covering.


Also, does it affect the acoustic performance of these tiles if they are painted?
Yes. Don't even think about painting them. :)

Regards,
Terry

hmmm... bummer. I thought I would save the expense of the fabric if I could simply paint the tiles. Plus, I'll have to paint the ceiling tiles black for the starfield... or I guess I could just cover those in fabric too. I just need to put a "loose" fabric that permits the sound to travel through to the tiles or fiberglass, right?

Anyone ever hear of "AudiMute Pro Acoustical Covering (NRC=.70)"? It basically looks like a quilted blanket that is supposed to be used for acoustics. Curious to see if anyone knows anything about it...

If it looks like a blanket, unfortunately, it will also likely perform like one. Good absorbtion in the highs and down into the mids and nothing on the bottom.

Lab report for this product can be found here:

http://www.audimute.com/AMP.pdf

Maybe you guys could help with interpreting the numbers or if this sounds legit. Would this product combined with some bass traps perhaps do the job???

Hi guys,

I decided to bring my HT questions to this thread since this is the one about acoustic treatment, so here goes>

See attached pictures to get the idea of what I'm talking about in the questions

1.- For high freq abs. I'll build 4 panels, put 2 in the right wall and 2 in the left wall, but I'll make an array. The 2 panel arrays I'm thinking would be composed of 2 2 X 4 panels and 2 2 X 2 paintings, all combined to form a big square, that absorbs the high f. and also decorates a little.

2.- What are the consecuences of hanging a large Horse painting in the back wall? Could I put something behind the painting to improve absorption?

3.- With all the information about bass traps I am really confused. Should I just buy a tube and fill it with dirt or sand? or should I build a couple of tick panels and put them on 2 corners? up front?

4.- I will put a rug on the floor, so should I also consider something for the ceiling?

5.- What sould I do about the front wall? another 2 2X4 panels on both sides of the TV?

6.- Is the back wall in need of diffusors?, maybe 1 difusor on each side of the Horse painting?

2.- What are the consecuences of hanging a large Horse painting in the back wall? Could I put something behind the painting to improve absorption?



Straw/Hay :D

HH

Lab report for this product can be found here:

http://www.audimute.com/AMP.pdf

Maybe you guys could help with interpreting the numbers or if this sounds legit. Would this product combined with some bass traps perhaps do the job???
Hi Todd,

This spec sheet gives numbers for G75 mounting. That means hung as a drapery, 75mm from the wall. This is such a rare spec that it's nearly impossible to compare it to any other material! It is only valid if you hang this product 75mm (3 inches) from a wall, which gives it a big bass absorption boost.

Regards,
Terry

Thanks Terry... I thought it was fishy, but I didn't know what the "catch" was...

I guess I'm back to 1 or 1.5 inch rigid fiberglass insulation and wrapping it in fabric. What do I need to look for and how much should I expect to spend? I guess I can compare that price to the price of the Armstrong Optima Open Plan tiles and go from there. I'll have to wrap either one in fabric.

I'm guessing that I'll also need bass traps to go along with the wall treatments...

I figured I would post my question in this thread rather than starting a new thread.

I have read thru the entire thread as well as read lots of recommended sites and I was able to get rid of about 80% of the echo problems I was having. First I insulated the right wall where the furnance room is which helped quite a lot, then I puchased some Roxul Safe N'Sound 3" insulation and placed it around the speakers and front wall to see if I could elimanate this wierd echo I was getting.

Well after watching some movies, I did notice that it was still there, althought not as bad as before and only during silent parts where the person is talking. This echo problem seems to happen only when something is coming out of the center channel. The problem doesn't seem to appear when I put the receiver in stereo mode. Also, I have the fronts and center bi-amped to an external amp, which is when I started noticing the problem.

Anyways, the echo it seems is coming from my Da-lite 16x9 screen. If you go under it and talk, you get an echo and you can tell it clearly comes from the metal around the screen. I have attached a picture and as you can see, my center channel is below the screen in the cabinet about 1/2 foot behind the screen, although the screen isn't covering it as the screen only drops to the top of the cabinet covering the television.


My question is, What can I do to get rid of the echo coming from the metal around the actual screen.

I will be shopping around for material to use to cover the insulation and I will do the mirror trick as well. I figure to use 8 of these between the front and side by the speakers. The room is 30' x 11' and has an opening to a hall between the first and 2nd row of seating.

Any suggestions on my next steps?

Thanks,

bgarner:
What happens if you hang a duvet/comforter down the back of your screen?

Haven't tried that but will get right on it to see what happens.

My suggestion would be to get that center channel out from under that shelf by moving it forward at least past the front of the cabinet. That, in itself, will cause some issues regardless of the screen.

Unfortunately, the Center Channel is bigger than the actual cabinet, so I don't have too many options. If I put it on top of the cabinet, then it will be louder when the screen is not down, if I set it up with the screen down and vice versa if I set it up with the screen not down.

Can anyone give me a ballpark price on what 1 and/or 2 inch rigid fiberglass should cost? Thanks in advance...

Also, can anyone tell me if a "basketball shorts" mesh fabric is OK to use... very porous, so I'm thinking it will be OK. Please advise...

Todd,

> ballpark price on what 1 and/or 2 inch rigid fiberglass should cost? <

A reasonable price for 1-inch thick 703 is 50 cents per square foot. Double that for 705 (twice as dense), and scale both linearly for thicker panels. Add a flat $1 or so per 2x4 foot panel for the FRK types, regardless of thickness or density. But be prepared to pay much more for small quantities.

--Ethan

From my supplier, the FRK facing products are over a 50% premium AT MY COST over unfaced. I've started the process of just getting the FRK scrim to sell so people can make their own - even then it will add about $2 to a 2x4 panel.

When building the panels, is it necessary to cover the back with fabric, or do you cover only the front with fabric? I will be using 3" Roxul insulation.

Any help is appreciated.

Brian