Regarding panel absorbers

[Osse]

Hello ppl, I've been searching the forum for panel absorbers but I didn't find any good info on them so I thought I'll start a new thread with some questions regarding them.

I've been reading Rod's book for a while and its great! However, when carefully placing speakers i'm satisfied with everything except in the room I experience a big peak in the 50 hz region, which I will need to handle for accurate hearing.

it peaks about 15-20 dB, here is a pic of the freq curve if you are interested.

http://img269.imageshack.us/img269/4803 ... aphic2.jpg

I'm thinking about building a panel trap centered around the 50 hz frequency to get some control over it.

The room is treated with a lot of broadband 4" 65 kg/m3 density rockwool which gives it a good character regarding reverbtime so instead of treating with more rockwool absorbers and kill the room I think panel absorbers will do the trick. The only concern for me is the 50 hz peak so to speak.

In the book, Rod say in the example that the current traps center frequency would in theory be 88.64 hz with a 1/8" plywood surface, and if you increase the thickness to 1/4" the center frequency would INCREASE to 126,18 hz. When I'm doing calculations with the formula in the book i'll get the opposite that thicker front panel would lower the center frequency, what's the deal here?

Also, he state that pressure devices(such as this one if i'm not mistaken) can be an "extremely efficient narrowband absorber", but the panel absorber has different paramenters affecting at least the centerfrequency, but what about the amount of attenuation in amplitude?

Is there any difference between the efficiency around the center frequency with lets say, deeper cavity/lower density panel compared to shallow cavity/higher density panel?

And what about the surface? What would give the best result, higher density with thinner matherial or lower density with thicker material, as long as it's the same weight?

Also, he states that if I avoid putting fibreglass in the cavity, the actual attenuation will increase but the Q of the panel will be more narrow. Now I wonder, does this mean the cavity BETWEEN the fibreglass(installed really close to the front panel) and the backing wall, or not using any fibreglass behind the panel at all? I mean, is the fibreglass installed close to panel supposed to be there, no matter what?

Hope i'm clear enought, and not asking stupid questions...

Thank you!
Ossian

[Osse]

Nobody?

[Soundman2020]

I've been searching the forum for panel absorbers but I didn't find any good info on

Maybe you tried before the update of the search engine last week. Right now, a search for "panel absorber" come sup with 491 hits, "panel trap" gives you 736 hits, and "panel resonator" produces 240.

I'm sure there must be some very useful information in that lot somewhere!

- Stuart -