dual purpose hanging absorbers

Hi guys. Just wanted to run this idea I had past you all to see what you think. Imagine a broadband absorber (timber frame filled with 100mm rockwool etc), but have the fabric over both sides, then have a thin wooden baffle with openings covering one side. (see included pics). The idea is that you could tailor the reflections in the room by either using the fabric side or the wooden side, but on the wooden side the traps are still absorbing lower frequencies whilst reflecting higher frequencies (like a non specific slat resonator). Do you guys think this would be a good idea? Thanks in advance, Oz

Ok, have develped the idea. To reduce weight, the timber sides could be removed, so that the absorber was basically a bag made to fit the rockwool slab attached to the front baffle. Agagin, any opinions welcome. Thinking of making these for my booth, and using the rail system I have seen on this forum to mount these to the wall. Thanks, Oz

I know you guys are all busy, but if anyone can advise me if this is a sensible idea or not, that would be fantastic! Thanks Oz

Hai Oz, Dunno, it seems like a fun thing to play with. Can't say anything else but; "nice going, sofar" :)

Hey Ro. Thats what I wanted to hear! Found a cheap supplier of Rockwool and Burlap, so will keep everyone updated on how they turn out! Thanks, Oz

Without sealed back/sides this is not a Helmholtz resonator. Bass trappping performance may suffer as a result. cheers Kris

Hey Kris. Yeah I figured it wouldnt work as a helmholz resonator as its not a sealed cavity. The idea was more about having the option of adding some liveliness to the high end response in my room, whist controlling some of the lower-mid areas. As well as these, there will be a large helhmolz resonator and a couple of super chunk bass traps, but i wanted some variable acoustic treatment. Could you explain why bass trapping would suffer as a result? Many thanks. Oz

what I meant is that by not sealing the sides, you end up with a pretty wide Q trap that doesn't reach very low in frequency (the helmholtz trap can get pretty low freq even for small depths when compared to pure absorbtion alone). Your idea will work in the sense that it will be somewhat reflective at the high end, and offer some bass trapping at the low frequencies, but I wouldn't expect it's low frequnecy absorbtion coefficient to peak as high as a true Helmholtz trap. Cheers Kris

i agree with the dr. plus the large openings will actually do more to absorb high frequencies than low ones. if you create a 3/4" plywood or 1" mdf place with routed slots from 1/16" through 3/8" and slats between 3.5" and 5.5" you'll probably hit the lower end and mids. if you leave an air gap between 2 thinner sections plus a gap off the wall you'll probably be a bit more efficient on the lower end as well. you can add the spacer and hanger on the plate as well to make it reversible. I'd put a layer of plastic under the cloth on the "absorber" side so its not completely sucking in all the highs...