Panel absorbers - insulation placement question

Greetings to all I'm going to make some sealed box panel absorbers but have a question regarding the insulation. As I understand it the insulation makes the Q wider, therefore absorbing over a wider range. If my panel is 90mm deep, insulation is 50mm - Is it OK to mount the insulation material against the wall - leaving a 40mm gap between the membrane of the panel and the insulation? Would there be any benefit is having the insulation mounted away from the wall? I'm guessing not but any advice is appreciated. Mudrock

There have been some heated discussions about that. You might wanna read this forum part a bit more... pages of mighty info awaits to be revealed to ya! It has been said that having a greater air space behind the box (and thus between wool and wall) will result in a lowering of frequency to get absorpted. Altho the panel still resonates on it's own frequency. I'm not an expert tho. again, read the board. There's some great debates on this between Eric and Ethan. (fun to read too, gheh. )

my understanding is that you want the insulation to be as close as possible to the membrane, without actually touching it. I don't think distance away from the membrane will affect Q or resonance frequency, as much as the amount of absorption given. The point of the insulation in a sealed-panel design is to dampen the resonance of the membrane, and if the insulation is too far away it will be less effective at this.

Thanks to both Ro and JWL I did have a trawl through the archive but there is no specific mention of the position of the insulation between the back wall and the membrane. Plenty of discussion about the merits of sealing the units airtight, though... I'm planning on keeping the insulation about 10-15mm away from the membrane - with a panel width of 60cm I don't think the semirigid insulation would touch the membrane. Cheers Mudrock

For the record, I know Ethan Winer, in his "build a better bass trap" article says that the insulation should be as close to the vibrating membrane as possible without actually touching it. Of course, anything Ethan says is subject to serious flamewars these days.... which from my point of view is unfortunate. I think he asks good questions, writes good articles, and has done a lot of good things for the acoustics community.... It seems to me that 10-15mm is too far, but then I don't have much experience with this type of absorber, so I'll let the experts chime in.

As long as the front panel don't touch the wool you're safe. The wool is to absorb air movement (waves) so indeed having them close to the panel looks like a good plan. As JWL said, Ethan's site is packed with information. There's not too much info on that topic out there so going with Ethan's advise is one of the few options available. Despite the flamewars, I think Ethan's the man when it comes to acoustic panels.

Ro wrote:

As long as the front panel don't touch the wool you're safe.

Exactly. > Despite the flamewars, I think Ethan's the man when it comes to acoustic panels. < Thanks. That war is over now anyway because I won. :) --Ethan

Ethan, you DO know there's no real winners in any war eh ;)