How many acoustic panels for my room?

CJ Paul · « **on:** 3 May 2006, 02:33 pm »

I'm wanting to basically hit a middle ground between good HT and good stereo acoustics and don't want to completely optomize one at the expense of the other. That said, given my room (22-24' x 38' x 8') (PICS) how many panels should I be looking for? I can do my own calculations of the fact that I may want to double or triple up thickness for corner bass traps. I'm kind of using this diagram of Ethan Winer's as a guide

I'm mostly wanting to get a feel for if you guys think I need 5 traps or 10 or 50. I'd rather buy more now and not use them but if 20 is more than I will EVER need in a million years then obviously buying 50 is a total waste.

My source for materials is 2" thick 3# density 2'x4' panels.

Thanks in advance!

nathanm · « **Reply #1 on:** 3 May 2006, 05:39 pm »

That's no room, it's a space station! My goodness, you could actually fit a genuine 5.1 circle in that cavern!

I say go for the 50 and donate any excess traps to needy audiophiles with tiny, square rooms!

It makes me wonder though - are the room modes with such an expansive space much less objectionable than the inevitably longer reverb times? The reverb would be much cheaper to treat than bass problems. Absorbing bass costs big money. I guess my question is, how does it sound now? I would assume you're not hearing lumpy bass in there with those dimensions. I'd guess upper mid echoes are more noticeable.

CJ Paul · « **Reply #2 on:** 3 May 2006, 09:13 pm »

Bass FR is not bad because I use a BFD. As far as reflections? Who knows, i mean, there there, my room is large but it doesn't defy the laws of physics so absorbing them has to benefit me some, right?

klh · « **Reply #3 on:** 3 May 2006, 09:31 pm »

The general rule is to try to cover 30% of the exposed surfaces with absorpbant material. If the floor is carpeted that helps a lot. What is the ceiling like? If it is exposed beams (like in an unfinished basement), you could hang fiberglass between the beams and cover it all with breathable cloth. That would be an easy way to get a lot of broadband absorption that would also look nice.

CJ Paul · « **Reply #4 on:** 3 May 2006, 09:44 pm »

Ceiling is completely finished sheet rock. I'm more wondering how I handle the back of the room since its not really in play. There is a good TWENTY feet behind my listening position but the eventual back wall is largely covered by drapes due to a window and patio door and there are the desks back there which kind of diffuse the sound a bit I suppose.

klh · « **Reply #5 on:** 3 May 2006, 10:08 pm »

Diffusion works well from a distance. It appears like you already have your answer

.

bpape · « **Reply #6 on:** 4 May 2006, 01:57 pm »

With the drapes and the carpet, you already have a great deal of HF only absorbtion. You'll want to get some more broadband and potentially some FSK faced material in there to balance things out a bit.

Start with the front wall and kill it totally. That won't hurt 2 channel much if they're out from the wall a bit and will really help HT. As you said, do some broadband bass absorbtion in the corners. Depending on how many seats and rows, you'll likely need at least 3 2x4 panels on each side wall for reflection control.

To keep the room somewhat live but still control the decay times, consider building some framed (1x3) 6"x48" absorbers. Mount them in an array on the side walls behind the listening position. Space them about 15" center to center. This gives a decent amount of control while also providing some pseudo-diffusion from the frames and the spacing.

Bryan

CJ Paul · « **Reply #7 on:** 4 May 2006, 02:10 pm »

Sounds good. Would it make sense to make them different depths too. Like have four 6" or 12" wide panels and have one frame be 2" deep and then 3", 4" and 5" deep or something?

Onlythat · « **Reply #8 on:** 4 May 2006, 02:47 pm »

A 'basic' set-up from Eighth Nerve acoustics or Echobusters or what have you.

Why not get the basic package covering corners and wall seams? Then you can always add panels for first reflection points etc. later.

Put up a basic package and see how she sounds first.

bpape · « **Reply #9 on:** 4 May 2006, 07:10 pm »

IMO, you'd not get much additional benefit from varying the depth of the 6" panels. Keep them at 6" wide by whatever depth. If you want the diffusion to be a bit more broad, use 1x4 instead of 1x3. That's a good compromise and not something that sticks out into the room TOO far.

For the corner broadband absorbers, you need some surface area and thickness. To be effective down below 80Hz, you're going to want at least 4" of thickness and at least a 2' wide face straddling the corner to get good spacing from the wall.

Bryan

Glenn K · « **Reply #10 on:** 5 May 2006, 01:14 am »

wow now that is a room.. The good news is you will not need so many panels per squ foot, but bad news is it still will take a lot of acoustics.. As Bryan said I would start with the front of the room and (well maybe not kill it but) treat it in the corners and maybe 50% of it. The work on the first reflections in the room. In most small rooms deffusion is not a recommend, but in this case I would put it on the back wall.

Wow what a room, oh I said that.. ha h ha.. You must post pictures.

Glenn

JLM · « **Reply #11 on:** 6 May 2006, 01:05 pm »

Larger rooms have less influence on the sound as the size of the space approaches infinity. Room modes will be at lower frequencies (larger sound waves). So my guess would be that you'll need to concentrate on low bass. But measure the room with your setup and equipment (make sure that speakers produce deep bass) first.

Too bad the ceiling isn't higher. Your room is three times the floor area/volume mine is, but I followed the Cardias room ratio formulas as my priority is audio over HT. You could do the same and just use the end 13 foot width of the room to produce an 8 ft x 13 ft x 21 ft audio room for yourself and then use the rest for family/HT. That's basically what I did and it helped eliminate the clastrophic low ceiling feeling.

bpape · « **Reply #12 on:** 6 May 2006, 03:51 pm »

While I agree that a larger room tends to make it a bit easier on you, the opposite problem that doing say 30% of the surface needs a LOT more treatment.

Also, as pointed out, since the primary modes are lower, they tend to be more difficult to deal with.

Also, remember that in a large space - air becomes a larger part of the equation. Air is a great HF absorber but that's about it. You'll still need to deal with the overall decay time across the frequency spectrum.

I would tend to agree with Glenn about the rear wall - but I'd try a series of different sized poly-cylindrical diffusors. They can be made large enough to be effective MUCH deeper than a QRD. This can also help with the modal issues. While it won't absorb them, if you can skew and disperse their return waves, it's harder for them to consistently cancel the oncoming waves at specific points.