Acoustic Foam behind inwalls?

Bluedog

I have Polk inwall speakers installed for my surround system, and I'm considering placing acoustic foam behind each one. Although they don't sound bad as is, I feel like I may be losing some sound behind the speakers. My surrounds are ceiling mounted in a vaulted ceiling, and the rear speakers are placed about 8 feet up on the rear wall.

Has anyone else tried this? Did it make a dramatic difference?

Wood Technologies makes an acoustic foam sound chamber that is designed for inwalls:
http://www.crutchfield.com/cgi-bin/S-n7y5pIwIRR8/prodview.asp?I=188SC1

Or alternately, I could just buy a sheet of "eggcrate " type acoustic foam and make my own enclosure. This seems to be the least expensive route.

Any advice would be much appreciated!

___________________________________
Receiver: Pioneer Elite VSX-45TX
Sub: PSW303
Center: CSi30
Front: RTi38
Surround: RC80i
Rear: RC55i

F1nut

Although I have no experience with inwalls, I think the sound chamber is an excellent idea. Polk has designed a inwall chamber to go with their new inwalls and you know Polk does it right.

dorokusai

Yes it is definetly recommended with installs such as yours. The Crutchfield type is only one that is commercially available. Mantis may chime in and direct you to some others. If he does not, the Wood Tech one is very nice and modestly priced.

Bluedog

Thanks for the feedback, F1nut & dorokusai!

I've ordered 2 pairs of the wood tech enclosures, and I'll post the results after I put 'em in.

wallstreet

I just filled the wall with pink insulation. Should accomplish the same result. In fact I would test both out since a roll of pink fiberglass insulation is way cheaper than an enclosure.

dorokusai

That is certainly a worthy route also Wallstreet, any kind of material behind the speaker is beneficial. Well, not any kind but you know what I mean. Good point.

There is actual "Acoustic Insulation" which would be good to use also.

Bluedog

I think that, in theory anyway, I'm going the right direction. I agree that pink fiber or acoustic insulation would improve the sound (better than empty space). But, my goal is to get the best possible sound from my speaker investment, so I'm willing to spend a few extra bucks to accomplish that.

I've done a little research on sound absorption properties. Here's the difference between eggcrate acoustical foam, and the Wood Tech enclosures (at least this is what they claim):

Eggcrate Acoustic Foam:
Sound Absorption Coefficients:
Hertz: 125 / 250 / 500 / 1000 / 2000 / 4000 / NRC
.35 / .51 / .82 / .98 / .97 / .95 / .82

Wood Technology SC-1:
Sound Absorption values:
Frequency (Hz) 125 / 250 / 500 / 1000 / 2000 / 4000 / NRC/AVG
1" thick .13 /.37 / .96 / 1.08 / 1.07 / 1.07 / .85

From this information, it appears that the Wood Tech enclosures actually let the lower frequencies through better than eggcrate, and absorb the higher frequencies more efficiently. It seems that this would be the best case scenario, since lower frequencies are not nearly as directional as higher.

So, it would seem that the imaging qualities of the inwalls would be improved - higher frequencies would not be dispersed into the walls (or the attic for the ceiling speakers), thus the sound would appear to be more directional from the speakers themselves.

But, as they say, an ounce of observation is worth a pound of theory. I'll know when I install the enclosures if it was money well spent!

mrgoodcheese

I'll be installing some RC60i in-wall speakers in my brother's new house soon. Thanks for the info so far.

Question though, how far from the back of the speaker (magnet?) should any sound absorption material be?

I'm concerned about having enough room, with the RC60i being 2 3/8 " deep and the wall being about 4-5 " deep after the drywall is on.

dorokusai

I don't think you can really get scientific in that space. If you mount, install or polyfill the area, it will be better than being empty.

I can't say wether closer or farther from the magnet would be better.

Bluedog

OK, so I received my Wood Tech enclosures the other day. I ended up ordering them from Efunctional.com, since they were way cheaper than Crutchfield.

I'm running a 7.1 surround system, so I started with the rear speakers (as they are the hardest ones to deal with). I had a little trouble removing the speakers, since I was paranoid about backing the screws out too far and dropping a wall clamp down into the wall. I finally got them out without losing anything by pushing the wall clamps out of the way with a coathanger.

The Wood Tech enclosures were a breeze to install. They come in four pieces, so each piece can easily fit in the hole in the wall. You just assemble them in the wall, and glue the pieces together with 3m Super77 spray-on adhesive. A couple of the pieces did not want to stay against the inside of the wall, so I just used a staple gun to attach them to the stud.

After re-mounting my speakers, I cranked up the Pioneer receiver on a local radio station and put it in 7-channel stereo mode. I was pleased with the results! It wasn't a night-and-day difference, but I could clearly hear a richer sound than before. The most notable difference seems to be in the bass and midrange. This was my first impression anyway.

Well, I ran out of time to install the enclosures for the ceiling speakers, so that will have to wait until next weekend. I'll post my results after I get those in.

dorokusai

Glad to hear the expected results Bluedog. The midrange and bass should be enforced with the backfill, its what those freq's need most in that application. Cool, let us know further results.

You should plan on posting a individual thread, as a review, if you are unhappy/happy w/ the results. That way a search will find it quick for the forum members and future. Just an idea.

simontan

Hi,

I got a pair of RC80i's for my rear surrounds and would like to know how the Wood Tech enclosures are working for you. I know you said it wasn't a 'night and day' difference on the wall mounts, but I would like to know if you a got a more noticeable difference on the ceiling mounts, since I'm a little disappointed with the sound on mine.