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post #10771 of 10789 Old 03-23-2015, 10:22 AM
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Originally Posted by KanosWRX View Post
Front wall yes, but the little bits to the left and right and the ceiling behind the screen wall probably not a big deal, talking maybe a couple feet in each of those areas. I haven't seen anyone specifically talk about filling those any for acoustic treatments.. but who know maybe it helps some, but its probably minimal. Best to get the front and back walls and bass traps and first reflection points, then your at least 75% of the way there.
My plan thus far is...the current 2" of Linacoustic behind the screen

Linacoustic filled fabric panels on rear wall
Linacoustic filled fabric panels on first reflection walls
empty Fabric panels the rest of the room...

first reflection on ceiling will be a future upgrade if needed.

Also Chunky bass traps in front corners behind screen

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post #10772 of 10789 Old 03-23-2015, 11:25 AM
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I found this article today which at least for me provides an understandable starting point. http://carltonbale.com/home-theater-...c-design-tips/

Framing out panels with Corning 703 in them is what I was already thinking about which I think would be easier to cover with black fabric vs trying to secure it cleanly directly on the wall. I just wasn't sure what I should use inside the panels.

The question that this leads me to is what fabric material to use? Originally I was considering black duvetyn for it's low light reflectivity and cost vs velvet, but how well will that work if you are trying to utilize the acoustic fiberglass inside the panels? Other threads I've read about making acoustic panels talk about using a fabric that is acoustically transparent (ex. Guilford of Maine). So essentially I'm dealing somewhat with a contradiction. Go black/low LR front, ceiling,floor, at least close to the projector and yet deal with decreasing/removing sound reflections in the front, sides near speakers.

btw, my front wall is Drywall on the inside. Behind it is a storage room with the backside still open. So if there is anything I would want to put in the wall cavity before I close it up I'd like input on that as well.
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post #10773 of 10789 Old 03-23-2015, 11:46 AM
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Originally Posted by adrian74 View Post
I found this article today which at least for me provides an understandable starting point. http://carltonbale.com/home-theater-...c-design-tips/

Framing out panels with Corning 703 in them is what I was already thinking about which I think would be easier to cover with black fabric vs trying to secure it cleanly directly on the wall. I just wasn't sure what I should use inside the panels.

The question that this leads me to is what fabric material to use? Originally I was considering black duvetyn for it's low light reflectivity and cost vs velvet, but how well will that work if you are trying to utilize the acoustic fiberglass inside the panels? Other threads I've read about making acoustic panels talk about using a fabric that is acoustically transparent (ex. Guilford of Maine). So essentially I'm dealing somewhat with a contradiction. Go black/low LR front, ceiling,floor, at least close to the projector and yet deal with decreasing/removing sound reflections in the front, sides near speakers.

btw, my front wall is Drywall on the inside. Behind it is a storage room with the backside still open. So if there is anything I would want to put in the wall cavity before I close it up I'd like input on that as well.

Seen that site before, good information there too. Always liked the look of the walls in his viewing room, but wondered if they might have too much treatment? He suggests 60-70% treated and that room is at 80%, I worry that it might end up too dead?


My room will be primarily for multi-channel sound (actually Atmos), so I need to take care with the treatments.

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post #10774 of 10789 Old 03-23-2015, 11:55 AM
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Originally Posted by Brian Fineberg View Post
My plan thus far is...the current 2" of Linacoustic behind the screen

Linacoustic filled fabric panels on rear wall
Linacoustic filled fabric panels on first reflection walls
empty Fabric panels the rest of the room...

first reflection on ceiling will be a future upgrade if needed.

Also Chunky bass traps in front corners behind screen
This has been the generel advice for the last 8 years at least in this thread, although the commercial experts tend to recommend what they sell, whether this is that every room is unique and requires a unique solution (those that sell such a service), or every room needs corner bass traps, side wall first reflection absorption panels, and front wall absorption treatment if using an AT screen (those that sell such standardized products).
There is a certain degree of egg and hen situation, as acoustic companies started by acoustic experts with a past as HT designers and builders will come up with products they have experience in works in customerized installations.

However, I also see a tendency in lots of experience coming from music studio acoustics, and I am not so sure any more that all that experience is transferable 1:1 to home theater.

For instance, the corner broadband bass trap (studiotips super chunks) 'standard' recommendation might and might not be needed/preferable in a HT. An alternative is the use of four corner loaded subwoofers, combined with quality eq. Or even two front corner loaded, or one center front wall and one center rear wall.
Four corner loaded subs will minimize a lot of the room modes, but you will not lose all that general mid bass to broadband absorption.
Of course, SSC bass traps are a lot cheaper than dual or quatro subs, but definately not without its price.

Another arguement is that requirements for music mixing acoustics might be different from what is a pleasant and natural sound when listening to music and moviesoundtrack in a HT room.
The mixer needs a flat frequency response, but not necesarily "a natural" / live music sound.

There is an acoustic school in HT that argues you should aim for what the mixer heard in the studio.

And there is a school that argues for less/no porouse absorption treatment and more diffusion (which often will have a degree of absorption due to turbulence and wave cancellation - or something like that :-) )

The latter school appreciates more lively rooms, as it resembles live music more. It also argues that we as humans are used to lively acoustics, despite its potential negative influence on dialogue clarity, etc., and that our brain therefor is used to compensating. Therefore, the argument goes, a flat frequency responsive but acoustically semi dead room will sound unnatural and actually stress our brain, making a longer stay in the room feel unpleasant - despite the perfect frequency response.

It is my argument that many of the rooms designed after the "code" in the beginning of this thread, i.e. 12 years ago, with one inch linacoustic or OC703 treatment on entire front wall and on side walls from front wall and 2/3 back, plus carpet, plus SSC corner traps, fall into this later description.

The first school would respond that it is the surround speakers that should create the ambience in a HT room, not 1st, 2nd, and tertiary reflections from the front speakers.

The second school would argue back that if the room is also used for 2 CH music, as a lot of smaller HT rooms appear to be, then there are no surround speakers (turned on) and a compromise is required.
A related arguement would be that even though surround speakers can create the lost (to absorption) rear hemisphere ambience, they cannot create the lost width of the front soundstage. You dont get the illussion of a wider-than-your-speakers concert stage or movie scene that high quality speakers can provide in a good 2 CH setup. 'Front wide speakers' actually try to recreate this lost ambience, but such speakers are not standard in most HT and have actually disappeared in DSU atmos upsampling.
The depth of the front soundstage that might be hurt by placing absorption behind the front speakers cannot be recreated in any way.

Another arguement from the second school might be that by optimizing clarity for multiple row multiple seats HT (by treating so much of the side walls), you pay a high price for the sound experience at the 2 primary seats in many small HT, that might or might not be the only seats occupied in 80 % of the time. Instead, only place FR panels for the MLP, or place narrow strips of absorption and diffussion on the side walls. Bryan Pape was making such an arguement in the beginning of this thread - dualing with Dennis Erskine of school 1.

In sum, I definately believe this thread needs a status post, with a FAQ.
As it is, I actually find it less than useful, and potentially harmful for users that 1) listen to 2 CH music as well as movies, 2) typically are less than four people in the HT (or less than four that worry about the finer details of acoustics), 3) design and build the HT based on 'common practice' from this thread without first hearing multiple rooms build with different acustical schools or paradigms in mind and 4) without having a room design so flexible that adding or removing acustical treatment based on the outcome of listening/testing/measuring sessions will not break or alter the visual design of the room in any negative way.

Cheers,
Jacob
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Last edited by Jacob B; 03-23-2015 at 04:12 PM. Reason: clarity - FRP panel added to the acoustic tone of the post :-D
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post #10775 of 10789 Old 03-23-2015, 06:42 PM
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Originally Posted by Brian Fineberg View Post
ive asked this a couple times in my thread but no answer...

behind my AT screenwall I have Linacoustic "sandwich" should I extend that on to the ceiling and side walls behind the screen?
Yes, Erskine specified covering the side and ceiling, as well as the front wall behind the screen. So I did that.
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post #10776 of 10789 Old 03-23-2015, 08:20 PM
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Originally Posted by adrian74 View Post
I found this article today which at least for me provides an understandable starting point. http://carltonbale.com/home-theater-...c-design-tips/

Framing out panels with Corning 703 in them is what I was already thinking about which I think would be easier to cover with black fabric vs trying to secure it cleanly directly on the wall. I just wasn't sure what I should use inside the panels.

The question that this leads me to is what fabric material to use? Originally I was considering black duvetyn for it's low light reflectivity and cost vs velvet, but how well will that work if you are trying to utilize the acoustic fiberglass inside the panels? Other threads I've read about making acoustic panels talk about using a fabric that is acoustically transparent (ex. Guilford of Maine). So essentially I'm dealing somewhat with a contradiction. Go black/low LR front, ceiling,floor, at least close to the projector and yet deal with decreasing/removing sound reflections in the front, sides near speakers.

btw, my front wall is Drywall on the inside. Behind it is a storage room with the backside still open. So if there is anything I would want to put in the wall cavity before I close it up I'd like input on that as well.
The fabric material has to be breatheable, i.e. if you put it close to your mouth and put your hand behind it you should be able to feel the air passing through it as you blow gently onto it. Guilford of Maine is a popular choice because it provides a clean look and finish, but it is relatively expensive. Personally, I, went for a black 100 percent polyester decorative fabric, but it is very thin so you can see the porous absorbing material (Knauf Insulation with ECOSE Technology) behind it. However, I fixed that problem by putting black 100 percent polyester wool batting (fleece plaid) between the decorative fabric and the Knauf. Polyester wool batting does an excellent job at preventing loose fibers from escaping, and it has sound absorption characteristics that are very similar to the layer of porous insulation material behind it. The layer of decorative fabric was not at all needed (nor harmful) in any way from an acoustics standpoint, but it sure did help to make the panels and bass traps look posh.


Oh and, BTW, here are a few interesting links to help people understand the basics about room acoustics:
http://arqen.com/acoustics-101/room-...aker-placement
http://arqen.com/acoustics-101/speak...y-interference
http://arqen.com/acoustics-101/surro...aker-placement
http://arqen.com/acoustics-101/room-...stic-treatment
http://arqen.com/bass-traps-101/placement-guide
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post #10777 of 10789 Old 03-23-2015, 10:45 PM
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Guilford of Maine is a popular choice because it provides a clean look and finish, but it is relatively expensive.
Guilford of Maine is also fire resistant.
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post #10778 of 10789 Old 03-24-2015, 02:41 AM
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Guilford of Maine is also fire resistant.
Yes, but then so is polyester. As a matter of fact, Guilford of Maine is 100 percent polyester.


P.S. - Below is a close-up picture of the fabric that I use. The packet shown in that picture measures about 4" wide.
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post #10779 of 10789 Old 03-24-2015, 03:01 AM
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In the book by Rod Gervais titled "Home Recording Studio: Build it Like the Pros", on page 207 you will find info on cloth covering for acoustic panels. (BTW, I googled for "guilford of maine fabric fire retardant", and page 207 of this book actually came up as the 3rd search result, it's on google books).
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post #10780 of 10789 Old 03-24-2015, 06:11 AM
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I found this article today which at least for me provides an understandable starting point. http://carltonbale.com/home-theater-...c-design-tips/
Some good tips in there but reading over it quickly there are a few things that are not correct.

Quote:
Fiberglass wall insulation is not dense enough. It’s designed to trap thermal air, not sound. It offers very little acoustic benefit because mid and lower frequencies pass right through it.
Actually if the panel or bass trap is over 6" thick less dense fiberglass will work better.

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A home theater room needs to have about 60-70% of the surfaces covered in acoustic absorption material. To get the best acoustic performance, you’ll want about 60-70% of your walls and ceiling covered. However, you don’t want the room completely dead.
In a way I can agree with this but it is not just about the amount the proper treatment in the right spots.
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post #10781 of 10789 Old 03-24-2015, 10:53 PM
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Folks,
Wanted some tips on what I could do to improve the low frequency performance of the speaker on the right. I am assuming the speaker on the left has better low freq performance because of the adjoining sliding door and back wall

Any diffusers or absorbers I can use for this setup that will allow for a more balanced output from both speakers
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post #10782 of 10789 Old 03-25-2015, 05:09 AM
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As a diagnostic move, shift everything left about two feet and listen again.

Probably the reflection off the short wall near the R loudspeaker is destructively interfering at your listening position. If that's the case, either a permanent relocation or significant absorption will help. The absorption would need to mostly fill the space between the short wall and the speaker.
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post #10783 of 10789 Old 03-25-2015, 08:49 AM
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Originally Posted by Dennis Erskine View Post
Compromise between the two playback scenarios is not a good option. Effectively you're saying you're (a) willing to spend a bunch of money and (b) happy to make the room sound poorly in either case.

If you have a good surround processor and a well set up multi-channel room, play your 2 channel recordings in multi-channel mode...a better result. I can assure you a good surround processor will do a whole bunch better job of creating the spaciousness than your room can accomplish.
Would you consider the Denon 4520 CI as one of the better surround processors? The reason I ask is because of the room and limitations on placement of equipment my system sounds terrible compared to other similar set up except they have dedicated HT Room for the most part. Thanks.
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post #10784 of 10789 Old 03-25-2015, 09:25 AM
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Probably the reflection off the short wall near the R loudspeaker is destructively interfering at your listening position. If that's the case, either a permanent relocation or significant absorption will help. The absorption would need to mostly fill the space between the short wall and the speaker.
I am also thinking that the short wall is messing up the low frequencies.
I could try relocating things to the left. Though using this as a permanent solution isn't an option. Need to keep things centered with the projector screen.
Not sure if this matters but these are back ported speakers.

How would absorption behind this R speaker help though? I would have thought we would want to use some kind of reflector behind this speaker (or to its side) to better disperse the sound that may be escaping because of the short wall?
Or an absorber behind the left speaker to dampen the low frequencies?
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post #10785 of 10789 Old 03-25-2015, 10:20 AM
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The fact that they are rear ported shouldn't make a difference unless you get really wild with the absorption and restrict airflow around the port.

The issue I'm speculating may be the problem is known as SBIR (Speaker Boundary Interference Response). The omnidirectional bass sound reflects from nearby boundaries and arrives at the listening position out of phase with the direct sound. The result is cancellation. The frequency of the cancellation is related to the distance between the speaker and the nearby surface. If the surface is farther than 3 feet or so, the frequency of the cancellation is low enough that the subwoofer has taken over and other room-related factors are dominating the response.

GIK acoustics has a very readable article about it here: http://www.gikacoustics.com/speaker-...response-sbir/

If this is, in fact, the reason for your problem, then adjusting position will be diagnostically significant even if you can keep it that way. The absorption could be effective by eliminating the reflected sound at the wall where it reflects - it can't be out of phase at the listening position if it never reflects.
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post #10786 of 10789 Old 03-25-2015, 01:24 PM
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Thanks HopefulFred. Let me play around with the placement of the speakers
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post #10787 of 10789 Old 03-26-2015, 12:37 PM
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Hopefulfred is pretty dead on. You have build up and or SBIR problems off that short wall. You could try some bass trapping in that corner and see if it clears things up. It would be better to move but if you can, then that is that.

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What's the best practice for treating 1st reflection points on the ceiling? Most of the recommendations I see are for broadband treatment using 4" OC703 or similar with a 2-4" air gap. I did some testing by holding up a 2'x4'x4" OC703 panel wrapped in FR701 and measuring with REW using a CSL calibrated mic. The results were not what I expected. The full band (20-20khz) measurements showed the gain of the ceiling reflection was reduced by over 8db. The 20-500hz measurement showed no reduction in gain of the reflection. This would seem to indicate the frequencies being reflected are >500hz.

Comparing the specs for 2" vs 4" OC703 shows the absorption coefficients at 500hz is only slightly better for 4". Above 500hz they are nearly identical. It would seem like 2" would be all that's needed in this case. Am I missing something here?

From Bob Golds
OC703 2" 500hz 1.14
OC703 4" 500hz 1.24
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post #10789 of 10789 Unread Today, 07:58 AM
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What's the best practice for treating 1st reflection points on the ceiling? Most of the recommendations I see are for broadband treatment using 4" OC703 or similar with a 2-4" air gap. I did some testing by holding up a 2'x4'x4" OC703 panel wrapped in FR701 and measuring with REW using a CSL calibrated mic. The results were not what I expected. The full band (20-20khz) measurements showed the gain of the ceiling reflection was reduced by over 8db. The 20-500hz measurement showed no reduction in gain of the reflection. This would seem to indicate the frequencies being reflected are >500hz.

Comparing the specs for 2" vs 4" OC703 shows the absorption coefficients at 500hz is only slightly better for 4". Above 500hz they are nearly identical. It would seem like 2" would be all that's needed in this case. Am I missing something here?

From Bob Golds
OC703 2" 500hz 1.14
OC703 4" 500hz 1.24
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