Acoustical Treatments Master Thread - Page 295 - AVS Forum
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post #8821 of 10377 Old 04-11-2012, 05:27 PM
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Yeah, thats why I asked Dennis before even considering a material to put up there. Thinking just fabric may be my best bet.
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post #8822 of 10377 Old 04-12-2012, 08:06 AM
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Quote:
Originally Posted by GRBoomer View Post

The idea with constant directivity waveguides (CD) such as Procella, Pi Speakers and the SEOS thread (in the DIY speaker forum) is that there is much less acoustical energy in the vertical so you do not have a typical high energy short delay reflection bouncing off the ceiling towards you. Yet, you get good, well controlled horizontal dispersion, to create a wide listening sweet spot. With waveguides, you do not have to correct, what's not there. Prevention versus cure.

In fact well defined horizontal control from waveguides also lessens the absolute, blind need for absorption at the first reflection point and starts to muddy the equation to diffusion being more beneficial to preserve the energy content in the room instead of trying to bury it all with fiberglass.

I really would invite you to read the following about early reflections before thinking diffusion is the way to go. The point is to hear that is coming out of the speakers not the speakers plus the ceiling reflection.
http://www.gikacoustics.com/news_020209.html

Glenn Kuras
GIK Acoustics

http://www.gikacoustics.com

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post #8823 of 10377 Old 04-12-2012, 11:40 AM
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First off, My room is 12x20x8.
The side walls are divided into 7x4 sections each covered with a 1" thick fabric frame. The back wall is divided into 4x4 sections.

Initially I had the 8 frames next to each corner filled with 1" OC 703. and the frames other than that had a checker pattern.

Given that configuration my speakers were toed in so that they intersect about 4 feet behind the MLP. If I make them intersect at the MLP they won't sound very good and they tend to hurt my ears at higher volume.

So I had some extra 703 laying around so I went ahead and covered the rest of the back wall with it as well as most of the side walls. The result was horrible. The room sounds very dead and I had to make the speakers point directly at the MLP to get it to sound anything decent. My guess is that before I was just hearing reflection of the two front speakers from the back wall. Now I think I am absorbing too much of the upper mid - high frequencies.

I do have 4 speaker stands each about 30" high for my surrounds that I filled with 5" oc 703. to act as bass traps. They are about 1 foot long and each 2 make a rectangle with the corner. ( I made that configuration up)

2" thickness is out of the question. So before I tear everything up to the way it was, I wonder if someone could give me any ideas.

Here is a link to pictures of my system to make it easier to visualize what I am saying.

http://www.blu-ray.com/community/gal...mber=ahmedreda

About my system:
Fronts Polk RTI A9, Surrounds RTI A5, Center CSI A6
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post #8824 of 10377 Old 04-12-2012, 01:33 PM
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I wasn't sure where to pose this question, but since professionals like Dennis E. visit this thread....

I have tried to create a retractable "black box" effect in my home theater room, using black acoustically transparent curtains that can be pulled along the side and back wall.

My projector is on a lift behind the viewing sofa, nestled in the nook of some bay windows, so in other words there is a bit of room space behind the viewing sofa. You can see photos in this post:

http://www.avsforum.com/avs-vb/showt...8#post18848458

So now I am going to be pulling an acoustically transparent curtain set behind the viewing sofa, to cut back wall reflections. There will be a cut out in the curtain for the projector to project through.

Sound issues aside: Will this create any difference in terms of heating or cooling in the room? In other words will heat tend to build up more around the projector due to it being curtained off in it's space behind the sofa? Or can I presume air, heat, etc, will transfer through the acoustic material roughly as sound will, and that there will be essentially the same thermal characteristics to the room as before?

Since we are always cautioned about how easily heat is lost through various materials, including windows, I just went into this figuring that heat would transfer pretty easily through pretty thin acoustic material.

(I'm wondering if adding this drape behind the viewing sofa will cause either the projector or people sitting on the sofa to become warmer, faster, compared to when we didn't have the drape behind us).

Thanks,
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post #8825 of 10377 Old 04-12-2012, 03:23 PM
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Sorry dragonfyr, I guess my post wasn't as clear as I thought.

The "creating a black box to kill back wall reflections" is for light reflections, not sound reflections. Mine is a projection-based home theater but I have light walls and I'm using the black curtains to kill light reflecting from the walls back to the screen (can't do darker walls for various reasons). Behind the viewing sofa is light wall, which is why I'm running a curtain across it. I chose acoustically transparent black material because that curtain is being pulled across my rear FX speakers (I have a 7.0 surround system), and of course I want to still hear my rear speakers.

However, I hadn't put too much thought into the heat issues, if there will be any.

Acoustically it's obviously not ideal - it does deaden the room a bit more. I'm hoping that doing running my AV receiver's Audyssey program with the new curtains in place will get some life back in the sound. I know it's limited and can't fix the changes in sound dispersion brought in the curtains, but I'm hoping it can help somewhat.

(Gawd I hate the spelling of "Audyssey." Trips me up every time...)
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post #8826 of 10377 Old 04-12-2012, 04:37 PM
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Thanks for your response. That was pretty helpful. I am planning to try the software you mentioned. In the mean while, I will take the treatment back to the way it was which I liked to a good extent.

I have one more question, Would filling those speaker stand with the 5-6" of 703 do anything for the bass (good or bad)?? They are not in the corner but they kind of form a rectangle with the corner. It is easier to understand by looking at the pictures. I kind of noticed a little better bass but it could be because I am missing all the high end reflections the bass seems more obvious.

Thanks a lot.

Quote:
Originally Posted by dragonfyr View Post

Lots of problems.

First, treatment for specular reflections (behavior above ~250 Hz) should be broadband.

Otherwise you only EQ the reflections and change the timber of the perceived sound - all while doing nothing to resolve the anomalies created by superposition of high gain reflections.

And 1" of porous absorption is good for little other than flutter echo.

Secondly, what should one imagine if the treat the rear sides and back of the room with absorption other than to create a deader space - to the degree that it EQs the reflections and fails to stop the destructive superposition?

Yes, you can guesstimate as to the polar dispersion of the speakers and you can guesstimate as to the optimal location for reflection control without knowing where the actual early arriving high gain reflections are incident - and simply deaden the room more than necessary in the quest and very possibly miss the actual high gain indirect paths.

And you can also figure out what acoustic response model you desire - but if you are placing absorption all over the rear and sides its hard to imagine you are interested in a later arriving diffuse soundfield that provides a sense of envelopment or spaciousness!

But after you figure out what kind of response you like, you can use (free) RoomEQWizard, (along with a calibrated Dayton EMM6 mic from Cross Spectrum and an ART Dual USB Pre mic preamp from B&H Photo for ~$69 delivered along with a mic cable , adapter and an RCA cable), to measure the room modes and adjust the seats forward or back to avoid the nulls, and you can make ETC measurements to identify the actual paths of the actual high gain early arriving reflections and place adequate broadband absorption at those points of boundary incidence and verify their effectiveness.

You can also determine if you want to control the later arriving reflections with absorption resulting in a 'dead room', or with diffusion, helping to preserve a sense of envelopment and space.

Depending upon the desired response, the ETC will provide a means to precisely place such absorption or diffusion treatment and will allow you to ascertain the spatial/temporal quality pf the resulting soundfield.

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post #8827 of 10377 Old 04-12-2012, 06:38 PM
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Quote:
Originally Posted by myfipie View Post

I really would invite you to read the following about early reflections before thinking diffusion is the way to go. The point is to hear that is coming out of the speakers not the speakers plus the ceiling reflection.
http://www.gikacoustics.com/news_020209.html

I did not say diffusion was the way to go. It is just with better controlled speakers, you may have other options than just trying to kill all the sound with absorption. And you lessen the influence of the ceiling reflection by not throwing energy at it in the first place.

I agree, measure and determine a strategy.
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post #8828 of 10377 Old 04-13-2012, 11:11 AM
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Quote:
Originally Posted by dragonfyr View Post

Oh, so the problem is that the reflections are not 'massive' enough???? LOL!
In my haste you definitely caught me!



Hmm...so we either need to figure out how to dim them, or to enable them to gain some weight... Let me get back to you regarding the latest best practices...

Your post is a veritable tar baby of double entendre!!!


Try as I may, I can not make heads or tails of this reply. (Or I'm not taking the right drugs?).

Anyone else have a reply to my question? Thanks.
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post #8829 of 10377 Old 04-13-2012, 11:45 AM
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Quote:
Originally Posted by GRBoomer View Post

I did not say diffusion was the way to go. It is just with better controlled speakers, you may have other options than just trying to kill all the sound with absorption. And you lessen the influence of the ceiling reflection by not throwing energy at it in the first place.

I agree, measure and determine a strategy.

"diffusion" is a very vague term as we use it in these contexts...

does the diffuser offer scattering only or true (flat power response) diffusion? spatial dispersion only? spatial + temporal dispersion? bandwidth of diffuser? minimum seating distance to diffuser (based on design frequency)? angle of incidence when it is mounted on a boundary (as it can alter bandwidth cut-off)? etc...

and in your first statement: "blind need for absorption at the first reflection point" --- bear in mind that large (with respect to wavelength) flat reflectors are more ideal than broadband absorption to redirect the high-gain indirect sparse early arriving reflection away from the listening position and towards the rear wall where it can be diffused and returned to the listening position as a laterally arriving, exponentially decaying diffused sound-field. eg, splayed walls (geometry) can be used for this in an example of a 2ch listening room. if you have rows of seats then it is likely not feasable - but the same goes for diffusion. lots of variables within the requirements... but absorption is most certainly NOT the ideal way to attenuate early arriving high-gain indirect specular reflections -

and there is no "blind placement at first reflection point" either, as one should ideally be measuring with the ETC to identify which boundaries are incident of the high-gain early arriving reflections, and attenuate/treat accordingly - but if one blindly applies broadband absorption at "all first reflection points", without knowing whether any issue exists there in the first place ... then that is a quick way to lead to a highly damped room!! if utilizing broadband absorption, it should be surgically placed only at boundaries incident of such energies as verified with the ETC to limit the amount of broadband absorption within the room. (and now you know why redirection is preferred to absorption) --- that is, unless the design goal is to create a highly damped room!
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post #8830 of 10377 Old 04-13-2012, 01:08 PM
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Quote:
Originally Posted by R Harkness View Post

Sound issues aside: Will this create any difference in terms of heating or cooling in the room? In other words will heat tend to build up more around the projector due to it being curtained off in it's space behind the sofa? Or can I presume air, heat, etc, will transfer through the acoustic material roughly as sound will, and that there will be essentially the same thermal characteristics to the room as before?

The thermal insulation properties of a single layer of acoustically transparent cloth are likely negligible, so I doubt you'll notice any temperature changes even with the material draped across three walls (left, right, back).

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post #8831 of 10377 Old 04-13-2012, 01:47 PM
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But the back "curtain" isn't on the wall, its in front of it, based on the picture, but about a couple feet. The curtain will impede air circulation (heat), so I would expect that area to warm up from the projector, but its still a good sized area, so probably wouldn't be a problem. What side does the projector pull and exhaust air from? Then again, I guess the curtain in the back needn't go all the way to the floor or even ceiling, if you wanted to leave a gap to let air flow.
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post #8832 of 10377 Old 04-13-2012, 02:16 PM
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Quote:
Originally Posted by dragonfyr View Post

If its not acoustical terms its basic English....
Look up the meaning of a "double entendre".

I know exactly what "double entendre" means. What I don't see is how you find my statements like:

"The "creating a black box to kill back wall reflections" is for light reflections, not sound reflections. Mine is a projection-based home theater but I have light walls

Mine is a projection-based home theater but I have light walls"


...To be rich sources of double entendre. What alternate meaning do they imply?

Quote:
Originally Posted by dragonfyr View Post

...And if you have to explain the joke...

...it's probably not a good joke. Or one should not be in the humor business?
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post #8833 of 10377 Old 04-13-2012, 02:18 PM
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Quote:
Originally Posted by sdurani View Post

The thermal insulation properties of a single layer of acoustically transparent cloth are likely negligible, so I doubt you'll notice any temperature changes even with the material draped across three walls (left, right, back).

Thank you!

If that's the case then my only real worries are alterations in the room acoustic. I do notice them (sounds more dead), but I'll have to see if room EQ can help enough for me to find it acceptable. (This is not a concern with listening to music in the room, since I do not have those curtains in use when simply listening to music, only when watching movies).
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post #8834 of 10377 Old 04-13-2012, 09:40 PM
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Quote:
Originally Posted by dragonfyr View Post

I have already made reference to some of them. If you can't see them even after several having been pointed out, well, then you are unable to identify double entendre.

I am glad you understand the definition, if not the actual 'thing'. Sorry if the references sailed past you...

But take a light hearted comment oh so seriously and in so doing call into question the understanding of the term itself as well.

No not serious at all, just wondering what joke I was missing. If it was all a play on "light," well, I guess we have different views on "funny," but no harm.

Thanks,
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post #8835 of 10377 Old 04-14-2012, 10:25 AM
 
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And it just keeps on going...

But hey, when in Rome...

...As if what I found bit bit ironic is dependent upon others 'getting it'.

And we wouldn't even begin to beg the issue as to why a question regarding light reflections and having absolutely nothing to do with acoustics is doing in a thread entailed "ACOUSTICAL TREATMENT MASTER thread"

The fact is there is plenty to smile about, if only in the all too common 'roll the eyes' 'oh brother' online forum manner.

...Next topic.....
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post #8836 of 10377 Old 04-16-2012, 07:00 PM
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Here are my bass traps installed.
Again I used tablecloths to cover the OC 703 and also dused two panels for this application
Attachment 243762

Attachment 243763

Attachment 243764

Also have the broadband panels 2 inches off the wall.

Now I am waiting for my 6 channell amp and new home made front chnnel enclosures.
LL
LL
LL
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post #8837 of 10377 Old 04-17-2012, 04:30 AM
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Hi all,

I'm looking at some DIY absorber panels. The commercial one I have at home has a membrane under the fabric that is described as "impact resistant L32 membrane". Does anyone know what this might be? or what I could use for it?

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post #8838 of 10377 Old 04-17-2012, 06:50 AM
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The L32 is for exactly what it states, to resist impacts. Those are used many times in high traffic areas (many times commercial/public locations) where the L32 prevents dents or impacts from damaging the panel.

In a home theater, I can't imagine ever needing that. Plus I am sure it would drive the cost up too.

For DIY, there are a number of build options. Some use rigid insulation like Owens Corning OC703, put a frame around it out of wood, metal, whatever, cover it with an acoustical fabric like Guilford of Maine (GOM) RF701, and hang it on their wall/ceiling.

There are other factors, like 2" vs 4" thick for the panel, and yes you will get increased performance out of it if you can leave a gap behind the panel between it and the wall/ceiling. So a 2" thick panel, sticking 2" off of a wall/ceiling surface would do very well.

Of course, there are other absorption that could be done in a room (bass traps, the entire front wall behind our speakers, etc) but you asked about panels.

Hope that helps. Others will probably have additional tips.
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post #8839 of 10377 Old 04-17-2012, 09:13 AM
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Some bass traps also use a sheet of kraft paper or 3-mil plastic film over the front. This reflects higher frequencies, and keeps the bass trap from absorbing them.
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post #8840 of 10377 Old 04-17-2012, 09:58 AM
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Quote:
Originally Posted by LeBon View Post

Some bass traps also use a sheet of kraft paper or 3-mil plastic film over the front. This reflects higher frequencies, and keeps the bass trap from absorbing them.

6mil plastic will begin to reflect specular energies ~500hz and up:
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post #8841 of 10377 Old 04-17-2012, 01:21 PM
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This is for a flutter echo problem in a living room, so I dont want to use the plastic on the front of it. I thought perhaps the membrane was something special that was firm(ish) and relatively AT (but 500hz and up reflection isn't helpful).

I was thinking I might put a thin layer of felt over the face of the panel before the fabric goes over, just so it is perfectly flat and uniform

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post #8842 of 10377 Old 04-17-2012, 01:38 PM
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If you're using Owens Corning 703 or another hard fiberglas, I have found that a little spray adhesive (like Scotch 77) directly onto the OC works well to hold the fabric (such as GOM FR701). Shouldn't need any intermediate fabric to get a nice-looking finish.
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post #8843 of 10377 Old 04-17-2012, 07:18 PM
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3M 777 is messy but absolutely works when applying fabric directly to the panel core.
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post #8844 of 10377 Old 04-17-2012, 07:30 PM
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hopefully not covering the entire porous outer face and possibly clogging the porous holes with the 3M adhesive...could have unexpected results and become reflective to HF content...
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post #8845 of 10377 Old 04-18-2012, 02:24 PM
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Quote:


This is for a flutter echo problem in a living room, so I dont want to use the plastic on the front of it. I thought perhaps the membrane was something special that was firm(ish) and relatively AT (but 500hz and up reflection isn't helpful).

In your case, likely true; however, while the membrane meets a couple of purposes with respect to LF performance, it is also used where additional LF absorption is desired but additional HF absorption would not be beneficial.

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post #8846 of 10377 Old 04-18-2012, 02:28 PM
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Quote:
Originally Posted by Dennis Erskine View Post

In your case, likely true; however, while the membrane meets a couple of purposes with respect to LF performance, it is also used where additional LF absorption is desired but additional HF absorption would not be beneficial.

Is there any resource you can point to Dennis that would help me wrap my head around why adding the membrane onto the face of a bass trap helps improve LF absorption?
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post #8847 of 10377 Old 04-18-2012, 03:36 PM
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Quote:
Originally Posted by Dennis Erskine View Post

In your case, likely true; however, while the membrane meets a couple of purposes with respect to LF performance, it is also used where additional LF absorption is desired but additional HF absorption would not be beneficial.

Thanks Dennis. Yep, LF performance isn't an issue in this instance - no membrane it is.

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post #8848 of 10377 Old 04-18-2012, 03:47 PM
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Quote:
Originally Posted by Brad Horstkotte View Post

Is there any resource you can point to Dennis that would help me wrap my head around why adding the membrane onto the face of a bass trap helps improve LF absorption?

Refer Toole, and Acoustic Absorbers and Diffusers from Cox and D'Antonio

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post #8849 of 10377 Old 04-24-2012, 01:54 PM
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OK. I've been searching, and obviously based off of previous posts, been following this thread.

I am planning on building front corner bass traps this weekend. I am stuck on the design/material question that people go 'round and 'round on.

I was originally planning OC703 or equivalent super chunks, then I was reading that the gas flow is more important, and something like R30 pink fluffy with a 34" face (what is that, about 24" for the other 2 sides) would work better for lower bass. If I decide that I can't give up 24" from the corner, maybe that Ultratouch R13 or R19 would be better.

Then elsewhere, I am reading that you need an air gap behind the trap. How does that work with a superchunk? I thought that the point was that they went into the corner?

So here are my goals with the bass traps (in conjunction to other acoustical treatments)
#1) Improve bass response and overall sound in the room.
#2) Provide a low cost, easy to construct bass trap.
#3) Looks are not important as they will be hidden behind a false screen wall.

I have pretty decent construction skills, but since they don't need to look like much, I am going for cost and functionality without being some ridiculous sized beast.

Please help.

(Notes: For now I am going to treat the whole front wall as well per instructions already received in this tread to make it a "dead" end. I will add the bass traps and see if the sound works for me. If not, I will look into FPR panels and/or making the read wall "dead" too. I want to get the big hitters out of the way that don't monkey with the WAF, and hiding this stuff behind the false wall scores big points with the wife just like hiding my SVS subwoofer will. )
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post #8850 of 10377 Old 04-29-2012, 10:27 AM
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Please help, I'm looking to add acoustical treatment to my HT.
I've attached a google sketch up (and .jpg) of my HT Room to scale.

I hate to leech (see below I've done some research and am stuck) but I've already put so much time into the creation of the room (i.e. away from wife/work/family/etc) that if I start a new "project" to get to really know sound acoustics, I'll "get in trouble" - so if someone can please look at my measurements and make clear/detailed recommendations for panels to add (where and what) and Bass traps

(orange box in middle is a couch (not actually orange))
Total Budget for this = ~$500 ($750 if really worth it)

============================================================ =====================================

Currently I have the following DIY info which I might fall back on
http://www.avsforum.com/avs-vb/showt...8#post21530858

Details :
room dimensions are: W= 10'3" L= 20'1" H=6'7" (note the front (part with black side wall) width of the room is 10'3, and the back (part with maroon side wall) is 9'8" wide
Floor is laminate w/ 7'8' area rug in front
Ceiling is DW+GG sandwich
Front wall and opposite side all (i.e. the wall you see in the pic) are 4layers of DW w/ Green Glue
Note -Other than about 2' from the floor and a few inches from the ceiling - the front wall is entirely the screen. Is so, does it need panels behind it?
Rear wall is cement with 2 shelves going lengthwise and the 2 rear speakers sit there.
side wall closest to you in pic (i.e. not shown) is cement w/a single piece of DW (hanging on a 2x3) in front of it

Speakers:cylinder sub woofer (SVS CS-29+) in middle/side of room.
equip = Klipsch RF-82II fronts, RF-64II center, RF 62 surrounds (only one is shown), 2 Mirage OMD-5 rear surround (not shown)

My research to date:
I've gone through the 1st 5 pages of this thread,
and have read through 1a-d) and 2a-b) of
http://www.gearslutz.com/board/studi...look-here.html and realize that I'm not going to be able to give the time to have a "pro" job done,
LL

 

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