Room Acoustics overkill or worse?

Would acoustically treating the ENTIRE back wall behind the speakers be overkill? This is mainly for aesthetic reasons. What I would like to do is to break up the back wall into 9 4’x3’x3” (WxHxD) modules and treat with Jon Risch’s design but flush with the wall. I have some questions regarding materials:

1. Can one substitute the fiberglass with poly bat entirely
2. Can anyone tell me if it’s a bad idea to use 1”, 40 grade foam sheet or a 1” coir sheet rather than the rockwool panel for the back.
3. Instead of burlap can I use raw silk. (wife’s suggestion)

For now I just have foam in different densities stacked behind the speaker (total thickness about 3”) and it made a huge difference. I also ‘stole’ 4 of my wife’s cushions and stuffed them with poly fill and have those in the corner which improved things even further. I would be happy if I got the same effect from the above design.

Thanks in advance for any comments/suggestions.
Unless you have dipoles or panels I would suggest you do the wall behind your listening position more than the wall behind the speakers. Doing all corners with superchunks will probably have the biggest impact....3" thickness is barely enough to do anything in the bass.
Absorption is what you are doing. Sonics will degrade if you cover with silk. So, a better bet would be to cover with speaker grille cloth. Check Parts Express for their black, 70 inch wide stuff. Inexpensive and very effective. Also, have you considered moulded form rollers that you could also cover the wall. The roundness creates better absorption. Here is a link.
Tweak, tweak and more tweak.

I wouldn't recommend over damping the room. It all depends on the room. Today most acoustical engineers and audio setup people prefer combinations of diffusors and absorbers.

An over damped room robs a system of vital presence and energy, so go slowly.
Maybe, maybe not. I looked for your Virtual System and you have nothing posted; therefore, we have no idea if you're using dipoles, rear ported, front ported, omnis or whatever. Also, we have no idea of the room size and reflectiveness of the remaining walls.

Generally, assuming the room is otherwise relatively lively, this will not be a problem. I take it your wife wants to cover the wall with silk fabric. Normally that's done over a light batting and would not be a problem. If you start adding thick absorbing material behind the silk, then you'll really deaden the room a lot.

Of course, you should look into LEDE technology. That's live-end-dead-end. This is used in some studios and demonstration room. The speakers are at the dead end of the room. It takes a powerful bass speaker to overcome the lost bass reinforcement. If you've got low ceilings and a narrow long room and need to place the speakers on a short wall, then this can be a good solution.

Anyway, generally, so long as you don't get carried away with absorbing material behind the silk, you'll be ok and that'll be a very nice listening room. Yes, you may need to move your speakers back a little closer to the wall, but that's no big deal. Any significant room changes will demand re-setting of the speakers.

I made 10 4" thick 2'x4' absorbers for the wall behind my speakers some time ago. They were constructed using open wood frame covered in a black fabric to keep a solid shape. I had also hung some Large PVC pipes from the ceiling in front of them to act as a pseudo room-lens diffuser. I thought it worked great at the time too. I certainly took a lot of effort (sounds butt ugly I know, but it was all hidden - see my virtual system).

Then last year I hired TM Labs to acoustically analyze my room before going even further with more treatments elsewhere (Best money I ever spent in audio BTW). It turns out I was already over-damped for 2-channel. On the HT side of things I wasn't too bad though. Since 2-channel is my priority, I removed five of the 4" absorbers and replaced four of them with diffusers. I also had to add diffusers to the wall behind me as per the TML recommendation in order to retest and pass certification.

This is a long way of offering to you that it really depends on your room and your set-up. To over-simplify, if you need 10 square feet of absorption, having that 10 square feet all in one place isn't going to work as well. WAF is a hard one to overcome. Mine said flat-out NO when I brought up 1" acoustic panels for around the room (doubles as a family recreation room). Then I made a small sample panel and she let me go-ahead. They turned out very nice looking with matching fabric. I think she was impressed...I know I was.

Regarding the fabric covering – anything you can easily breathe through should work OK. For my 1” panels I used some nice fabric I picked up at a local fabric store that matched the wall color. The fabric was the most expensive part of the panels BTW. For my rear diffusers I ended up just going straight to Guilford of Maine material.

If you wish, email me and perhaps I still have my construction pics around somewhere. It was a couple dead computers ago, so no guarantee.

Good luck,

thanks for all the replies suggestions. I should have described my setup better. Sorry I have to get down to posting my system soon............

The room is 15'x12' with a sloped ceiling along the shorter wall. I have large french windows along one of the 15' walls and an 8' opening on the opposite side into a double ht. living room. The walls are 9" brick with cement plaster. The ceiling is concrete, but covered from below with pine wood slats. The floor is a hard cement mosaic floor. Typical construction in India.

The speakers consist of a pair DIY 15" subs, which are ported at the back and a pair of sealed MTM's along the shoter wall. I have have no resonance from any of the cabinets. Solid 1 1/2" MDF. I usually put a carpet on the floor. I also have a 25" TV between the speakers.

So far the foam treatment has really cleaned up and tightned the sound. The most pleasing change has been the increase in scale and body of the instruments. I wanted to put panels behind the speakers and in the corner but better half frowns at that idea.................
Great, your description is a BIG help. Yes, your room, particularly with 15" subs, can probably use a ton of damping. Have at it. You could make the speaker end almost totally dead and it wouldn't be a problem. As it is, I can't imagine that the speakers are not overpowering the room. Thankfully the walls, floor and ceiling are sturdy, so you can probably get a quite nice result deadening one end.

Here's very important advice from someone married almost 40-years, et the wife get the silk. ;-)

That sounds like a very lively room! As to the specific question, I can attest that too much treatment can degrade the sound. I moved my system into an untreated room with absolutely nothing on any wall or window. It was like an echo chamber in there. I purchased a room treatment kit from Auralex and went to work. The kit included more treatment pieces than my room required, as I had some DIY panels, but that didn't stop me from using them.
I would listen as I went along and it did get to a point where I was noticing a degradation in the sound from too much absorption. I removed some treatment until I got it correct, or what I thought sounded best. Some of what I removed was behind the speakers. A totally dead wall does sound like overkill to me but your ears will judge. Good luck and do post your system. I'd be interested to see the outcome.
thanks for the advice. The reason for making it in modular form was to have the option of removing a panel or two if required.

Any suggestions on using the coir vs rockwool?
one last question on this topic before I start on the wall. What frequencies does the rockwool panel control and what frequencies does the fiberglass insulation absorb?