Home Room Acoustics Forum by Rives Audio

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On the subject of membrane absorbers...

Mass aside, does using a stiffer material like gypsum for the membrane result in more reflection and less absorbtion? Conversely, does using a more flexible material for the membrane (other factors being equal) result in more absorbtion? For example, low density fiberboard ceiling panels, compared to .5 inch plywood? This is not just a theoretical question. I'm planning to put a trap at the top of my stairs, because there is a boom in there that is pretty annoying to anyone upstairs when the music is turned up. The boom seems to be primarily 54 Hz, the 2nd mode in the 21 foot long space. I've been thinking about how to optimize a trap for such low frequencies without intruding severely on the landing at the top of the stairs. Your low bass panel trap does reach into this range, but might be tweaked to be more effective. A heavier panel would lower the peak frequency, but intuitively it seems to me that a thicker piece of plywood will be stiffer, and reflect more / absorb less sound. Deepening the air space is another option, but a 6 inch or so deep trap is going to cramp the landing a lot. However I could put a 6 inch deep trap on the ceiling over the landing. I have spare ceiling panels and they turned out to weigh .79 lbs per sqaure foot, just a bit more than .5 inch plywood. I thought, as these panels are not as stiff as plywood, they might reflect less and absorb more sound over their whole range. I could even stick a linoleum tile (another thing I have lots of spare) on the inside to weigh the panel it down a bit, without adding significant stiffness.
Or am I misunderstanding the whole membrane trap mechanism? Would a less dense panel material just let the low frequencies pass through? Assuming I build the trap correctly, not just hang a tile there.
I realize that to get a really major improvement, I'll probably need to treat both the wall and the ceiling.


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