# Input on perforated panel absorber.



## clausdk (Jun 28, 2007)

Hello everyone.

I've been trying to obtain bass nirvana :rubeyes: and I've come to the conclusion that I need some hefty bass trapping if I'm to ever get there!

I've downloaded a program to design *perforated panel absorbers*.

My room is 18,3x16,1 giving me room modes at around 31hz(length) and 35hz(width). The height in the room is 8 feet near the walls but in the middle it's 10 feet. Averaging that to 9 feet gives a room mode in the height around 63hz.

These room modes are confirmed by numorous REW measurements and I've dailed in my behringer 1124 DSP to the best of my abilities to control the modes.

As confirmed by REW waterfalls and spectrograms I have serious ringing in the whole 30-40hz area which more or less combines to one big troublearea!

Also there are noticable ringing in 60 and 70hz, however it appears that the 30-40hz region is causing more trouble.

My plan is to build 3 large perforated panal absorbers measurering 60x120cm/2'x4' and 30cm/1' deep!

I will install them behind our couch and put a board on top as a shelve and line them with some fabric.

Here's my design so far:

*16mm MDF front
*0.39% perforated with 10mm diameter holes, around 24 holes (Excel program says radius 10mm, but I'm uncertain it should've said diameter?)
* Depth 30cm
* 20cm mineral wool against back on cavity, leaving 100mm air gap to perforated front panel.
* Resonate frequency 35.5hz. Peak 0.9 absorbtion.

Alternating the numbers just slightly tunes it to 31hz.

Plan is then two panels tuned to 31hz, one at 35hz and to adress the 70hz+ problem I would use 100mm broadband absorbers around the room.

*Suggestions and input please!*

- Calculations correct?
- Any experience with perforated panal absorbers?
- Will 3 large 2 by 4 feet, thats a total of 2 by 12 feet absorber have any noticable effect on this low frequency problem?
- Other suggestions to solving the problem?

Before I get started on these massive cabinets! any input is appreciated.

Regards

/claus


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## bpape (Sep 14, 2006)

Just remember that perforated Helmholz type absorbers are very very narrow in nature. They're usually added after doing proper broadband treatment which will cover the more broad spectrum rather than just 1/2 octave or less.

Also, using perforated absorbers down around 30Hz is kind of problematic. They can very easily introduce their own problems into the space. IMO, for those things, I would recommend more of a rigid membrane type of absorber which is slightly wider in function (about 2 octaves) and doesn't have the problems of it's own resonances when tuned that low.

Bryan


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