Acoustical Treatments Master Thread - Page 109 - AVS Forum
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post #3241 of 10427 Old 04-11-2008, 11:31 AM
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Quote:
Originally Posted by pepar View Post

Well, I certainly will defer to bpape's experience, but is your entire back wall treated?

My room is 16' wide, with a 10' high ceiling. Soffit and light shelf take up two feet, so the side/back walls are 8' high.

The middle 11' of the back wall, 8' high, will be treated with 2" 703. The angled entrance area near the door won't be, and there is a closet door on the rear right that won't be. See my sig for a link to pictures that may help understand.

One problem I can see with not treating the back wall: It is a first reflection point! My rear seat ears are only 3-4' from the back wall. Back wall reflections will likely be even closer in time than side wall reflections for the back row.

We'll see how it goes.

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post #3242 of 10427 Old 04-11-2008, 11:38 AM
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Quote:
Originally Posted by pmeyer View Post

Makes sense. I can see two issues:
- just walking around the room, if it sounds like one of those anechoic chambers, it might be a bit wierd.
- surround 'atmosphere'.

I hadn't been too worried about the former, but the latter makes sense. In an ideal world you'd have a totally dead room and some kind of speaker array on all sides. 256:12 sound tracks, with a fully enveloping set of speakers.

In the real world, especially with dipole side speakers not pointing at the listeners, if you have a totally dead room you'd hear very little from the sides at all. I hadn't thought about it that way...

The LEDE (live end-dead end) stuff is a holdover from 2-channel reproduction. No clear and unanimous path has been arrived at for multi-channel. I've got the dead end part down quite nicely, especially with the addition of the superchunk bass traps. As for the rest of the room, with the exception of the rear wall first reflection point absorber, I feel that what I have done is not quite right for 7.1.

Just my $.02.

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post #3243 of 10427 Old 04-11-2008, 11:41 AM
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Quote:
Originally Posted by pmeyer View Post

One problem I can see with not treating the back wall: It is a first reflection point! My rear seat ears are only 3-4' from the back wall. Back wall reflections will likely be even closer in time than side wall reflections for the back row.

We'll see how it goes.

Try treating only the exact first reflection point.
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post #3244 of 10427 Old 04-11-2008, 11:59 AM
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Originally Posted by pepar View Post

Try treating only the exact first reflection point.

I could do that. It would be pretty much the full width, but would only need to be between 3-6' off the ground. For now I'll stick with the plan and see how it feels.

The easy thing would be to make the rear row have high back chairs. Problem solved.

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post #3245 of 10427 Old 04-11-2008, 12:07 PM
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I just realized something: I left out critical information (and am not accurately representing Bryan's plan).

The rear wall is completely covered with 2" 703 *with FSK* (aka the paper insulation cover). It will therefore act as some absorption in the middle, but not low (too thin) or high (paper). The sides and front are the same as mentioned above.

This will help: [edit: this is Bryan Pape's plan]


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post #3246 of 10427 Old 04-12-2008, 07:44 AM
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Paul--I'm not a technician, so I fear this will sound stupid! I'm firing away, anyway...

On your diagram, what are the yellow boxes on the very bottom that look like they are another set of L/C/R with what appear to be the reflections coming off them?

Is that just the 1st reflection pattern?

Also, how do the bass absorbers work placed directly in your double-door way?

Thanks for any insight!

Best to you,
Phil

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post #3247 of 10427 Old 04-12-2008, 08:50 AM
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I didn't mention it, but that is bpape's plan for my room, I can't take credit for it.
The 'virtual' speakers are just reflections of the front speakers through the left wall to make it easy to draw the first reflection points. If you draw speakers on the other side of the wall the same distance from the wall as the main speakers, and then draw a straight line from them to each head, the intersection with the left wall is the reflection point. Easier than trying to measure all the angles.

As for the bass trap over the door, it's shown as two, but I'm actually doing it as one:



The attic over the left wall/door is actually about 6-8 feet above the ceiling, so I have room to walk around up there. I cut back and rearranged some ceiling drywall supports up there and carved out a 2.5'x4'x2'deep bass trap in the ceiling over the door. It'll be covered with some kind of cloth panel (tbd).

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post #3248 of 10427 Old 04-12-2008, 09:01 PM
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Pmeyer...In your analysis, it says bass absorbers 17x17x24 from bulk Cotton.

What is bulk cotton? it can be used instead of rockwool or oc703??

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post #3249 of 10427 Old 04-12-2008, 09:11 PM
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It's normal house insulation created from recycled blue-jeans. Here's a link for a picture (this isn't the brand I got, I just googled for cotton insulation r-13)

cotton insulation

Mine is similar to that, but thicker (about 5") and 24" wide.

The only reason Bryan marked my bass traps that way is that I've got three rolls of it lying in the garage and had a local source. It's a lot easier to work with than fiberglass. I picked up three rolls at one point. Unfortunately, my source (Eco-wise in Austin) temporarily doesn't carry it any more.

I'll probably still do my front bass-traps out of 703. My back right bass trap is big enough and deep enough that I'll probably use the cotton. Especially since I can compress it vertically and get it a bit denser in the frame back there.

I don't know what I'll do over the door. 2x4 sheets of 703 will fit up there nicely and will be easier to hold up than the floppy bulk cotton would be. If I do cotton, I'd need to build some kind of grating to keep it from coming down, and compressing it would be difficult.

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post #3250 of 10427 Old 04-12-2008, 09:37 PM
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Hmm, for fabric covered walls, that acoustic cotton looks nice. No harsh fibers, similar price to 703, and good coefficients. Other than it's lack of rigidity, are there any cons I'm missing?

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post #3251 of 10427 Old 04-13-2008, 05:44 AM
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Its thickness. Look up "Bonded Logic Inc's UltraTouch Cotton" r-13 on Bob Gold's absorption site. The 3.5" thick stuff is very effective (95% down to 125 Hz), but it's 3.5" thick!

I thought about coming up some crazy 2' wide cutter to slice the 3.5" stuff into 1.75" halves and use that (slightly compressed) in a 1.5" frame, but it didn't seem worth the effort.

Interestingly, the stuff I have has a certain amount of plastic fibers (polyester? nylon?). If you compress it and heat it, the fibers melt and it retains it's new thickness/density. I thought about trying to 'densify' my cotton a bit and make it thinner. Again, I couldn't think of a practical way to do it. The acoustical properties of what I had in the end would be unknown anyway.

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post #3252 of 10427 Old 04-13-2008, 05:55 AM
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Quote:
Originally Posted by pmeyer View Post

Its thickness. Look up "Bonded Logic Inc's UltraTouch Cotton" r-13 on Bob Gold's absorption site. The 3.5" thick stuff is very effective (95% down to 125 Hz), but it's 3.5" thick!

Compare with AcoustiCotton, right above it on Bob's page. Or Echo Eliminator bonded acoustical cotton, right below it.

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post #3253 of 10427 Old 04-13-2008, 07:24 AM
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pmeyer, thanks that is an interesting alternative. I have corner bass traps to fill also and I might use that instead of the more rigid Rockwool 60.

Heck its cheaper and better if you compare 3.5" vs the Rockwool 60 2".. I already spend $150 on the rockwool. I could have spend $160 (edited, shipping is $60) on this stuff and it has better numbers

I wonder why its never talked about before, I guess I just missed it.

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post #3254 of 10427 Old 04-13-2008, 09:06 AM
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You need to be careful comparing. It looks to me like 4" rockwool has about the same numbers as the 3.5" cotton. I'm betting 2 layers of 2" rockwool are the same as or better than 1 layer of 3.5" cotton.

It comes down to what you can get, what is cheap, and what is easy to work with.

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post #3255 of 10427 Old 04-13-2008, 09:18 AM
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Quote:


You need to be careful comparing. It looks to me like 4" rockwool has about the same numbers as the 3.5" cotton. I'm betting 2 layers of 2" rockwool are the same as or better than 1 layer of 3.5" cotton.

It comes down to what you can get, what is cheap, and what is easy to work with.

Well to get the same sqft..I think its about the same cost for 2" vs 3.5" so that alone shows me that the UltraTouch stuff is the better buy, much better coeffecient at low frequencies.

R-13 3.5" (mm) A 0.95 1.30 1.19 1.08 1.02 1.00 1.15

vs

RXL 60 2" 0.32 0.81 1.06 1.02 0.99 1.04 0.95


I was using the Rockwool60 in the corner traps, which will have a frame just like yours. I had to cut the 2x4 rigid sheets to fill the frame. Now I can easily fill the frame with long lengths of the ultratouch, compressing it together is I add more layers. I just seems so much easier in my books.

I just purchased 106 sq ft of the stuff....I will fill one corner trap with it and another one with the Rockwool 60 I own.

Some lucky member will probably get a great deal from me, I think I have too much OC703 and too much Rockwool 60...but we shall see.

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post #3256 of 10427 Old 04-14-2008, 06:40 AM
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Actually, the 2" with a facing is relatively good down reasonably low.

Coefficients:

0.63 0.56 0.95 0.79 0.60 0.35

There's a bit of a hump in the middle but it's still respectable down at 125Hz and lower. Just helps in the length dimension with midbass boominess and giving some broadband control opposite the screen area without killing the highs on the back wall in the surround field.

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post #3257 of 10427 Old 04-16-2008, 06:07 AM
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Quote:
Originally Posted by penngray View Post

Some lucky member will probably get a great deal from me, I think I have too much OC703 and too much Rockwool 60...but we shall see.

Hold onto it! Properly used and placed, this is a pile of gold.

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post #3258 of 10427 Old 04-16-2008, 06:34 AM
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I just was using that reflection program from this forum and it shows a reflection on the ceiling.

I dont read much about ceiling treatments. Im thinking that after everything is done, I might build a 2x4 panel and place it on my ceiling at the reflection point.


Quote:


Hold onto it! Properly used and placed, this is a pile of gold.

Yeah, its nice to have too much just in case. I also think my bass traps will be better now because I can go thicker with them.

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post #3259 of 10427 Old 04-16-2008, 08:13 AM
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Quote:
Originally Posted by penngray View Post

I just was using that reflection program from this forum and it shows a reflection on the ceiling.

I dont read much about ceiling treatments. Im thinking that after everything is done, I might build a 2x4 panel and place it on my ceiling at the reflection point.

Ceiling reflections may or may not be a problem. If you happen to be using THX front speakers, then they will probably not be. This is because the required dispersion pattern for a THX main is wide horizontally, but narrow vertically.

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post #3260 of 10427 Old 04-16-2008, 08:22 AM
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if GOM is too expensive a fabric for me, but I don't want the farm smell of some burlap, what would be a good mid-end fabric that passes the blow test and comes in a variety of colors?

I went to JoAnn's, but it would've taken me hours to blow through every damn fabric. Plus I'd look like a complete moron blowing on every fabric!

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post #3261 of 10427 Old 04-16-2008, 08:34 AM
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Quote:
Originally Posted by Terry Montlick View Post

Ceiling reflections may or may not be a problem. If you happen to be using THX front speakers, then they will probably not be. This is because the required dispersion pattern for a THX main is wide horizontally, but narrow vertically.

Regards,
Terry

That is a very good point. THX-certified speakers have very tightly controlled vertical dispersion just for this very reason - reduce/eliminate ceiling (and floor) reflections. Having said that, and in line with my "I think I did too much" feeling, I did place a front ceiling absorber, which I am now considering removing (and possibly replacing with diffusion). I have THX Ultra speakers.

Pics here.
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post #3262 of 10427 Old 04-16-2008, 08:45 AM
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Quote:
Originally Posted by ImkSpyPlns View Post

if GOM is too expensive a fabric for me, but I don't want the farm smell of some burlap, what would be a good mid-end fabric that passes the blow test and comes in a variety of colors?

I went to JoAnn's, but it would've taken me hours to blow through every damn fabric. Plus I'd look like a complete moron blowing on every fabric!

Muslin will work well for treatment covering and is very inexpensive. It is not, however, suitable for in front of speakers. It's also not a fire rated material.

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post #3263 of 10427 Old 04-17-2008, 12:21 PM
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Quote:
Originally Posted by bpape View Post

Muslin will work well for treatment covering and is very inexpensive. It is not, however, suitable for in front of speakers. It's also not a fire rated material.

Bryan

Thank you. It won't be in front of speakers.

BTW, appropriate that you replied, I have a order on its way from GIK as I type this. Tri-corners and some 442's. I'm finally getting around to treating my extremely small room. Of course I do it now after I spent the last few days tuning my system as best I can. When I get the treatments in, I'm sure I'll have to re-tune.

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post #3264 of 10427 Old 04-19-2008, 06:03 AM
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As for treating rear wall reflections from front speakers, this is often not necessary. Unless you are very near the rear wall, the reflection will not occur within the first 15 milliseconds or so of the direct sound. This means that your brain cannot merge the two sounds into a single sound with degraded spatial localization.

Also, unless you are very near the wall, any significant notch filtering due to interference between direct and reflected sound will be very low in frequency -- low enough to be absent because it has been offloaded to your subwoofer by your bass management system!

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post #3265 of 10427 Old 04-24-2008, 05:42 PM
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Have now completed acoustic treatment prototyping.

I had a real problem with bass modes in my screen 'alcove' in the front of the room so I choose to treat the entire alcove with 4" mineral wool (covered with 1" linacoustic - cheaper than GOM)

2'x6'x4" bass traps in the rear corners; and

48" high panels of 1" linacoustic on the side walls (just cut pieces of linacoustic - have not framed them yet)

See before and after RT60 and Freq response below (note before is red, after blue)





Please note that I have 4 subs in 1/3 2/3 positions on the front and rear walls.

Have to say the RT60 may be a bit low. I may scale back the side panels a bit.

However, the room sounds very good, albeit a bit dead. Whenever I listen in a room like this I like to say that it ruins all my recordings. I hear every error in mix, artificial reverb, MP3 (my library is in iTunes) encoding compression, etc. But when a recording is good, its great!

All comments welcome!
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post #3266 of 10427 Old 04-26-2008, 05:36 AM
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Here is some more data from the prior post. Impulse and waterfall





On the impulse response, I have identified the first 3 large impulses as the following:

3ms - ceiling first reflection. When I temporarily placed a piece of linacoustic at this reflection point the peak decreased 10db - strategy - will treat

6-8ms - reflections from along the length of the soffit vertical portions - this section is only 8" high but is clearly causing substantial reflections - when I placed a temporary piece of linacoustic here, the reflections decreased 8db - strategy - will treat

9-10ms - side walls, already treated with 1" linacoustic -might be column edges also - likely leave be. Perhaps add another layer?

General questions

How is the performance of this room?

Once treated, are the first reflections sufficiently mitigated (per above)?

Is the RT60 too low (see prior post)?

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post #3267 of 10427 Old 04-26-2008, 05:55 AM
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db,

The only reflection that really needs treatment is the ceiling reflection at 3 ms. The other reflections are low enough not need treatment.

What are the dimensions of this room?

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post #3268 of 10427 Old 04-26-2008, 07:27 AM
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Thanks Terry - Here is a rough sketch (dimensioned)

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post #3269 of 10427 Old 04-26-2008, 07:28 AM
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Hey db,

What equipment are you using to generate your measurements and graphs?

That's great news from Terry about only needing to treat your ceiling, eh?!

Have you got any pics of your room--I'd love to see your quad subs!

Keep up the great work,
Phil

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post #3270 of 10427 Old 04-26-2008, 07:58 AM
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Hi db,

I'd say that your reverberations times in the octave bands 125 Hz and 250 Hz are a bit too high relative to the higher frequency octave bands. These higher frequency octave band reverberation times are not too low on an absolute scale, but too low on a scale relative to the 125 Hz and 250 Hz octave bands. This unevenness can make the room sound too dead. As for the 63 Hz octave band, reverberation time measurement at these low frequencies is too unreliable in small rooms to be useful.

But since your upper frequencies are fine, you just need more absorption at the highly treatable 125 Hz and 250 Hz octave bands. I recommend either DIY bass traps, as described in this forum and on http://forum.studiotips.com/viewtopic.php?t=535, or ready-made bass traps by forum members RealTraps or GIK Acoustics.

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