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Re: question about how to put gypsyum boards

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Ethan Winer

(M)

In Reply to: question about how to put gypsyum boards posted by ponz45 on February 15, 2006 at 18:01:53:

Ponz,
> is there any way a i could distribute them , in a way that some of them could actually act as broadband bass traps? <
I don't think you'll be able to get much "broadband" trapping that way. Further, a wall material that's thin enoguh to absorb at a usefully high center frequency will not have enough mass to also block sound. More to the point, with a tuned construction like that, there will be reduced isolation at the center frequency. This is the nature of membrane absorbers.
--Ethan

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On the subject of membrane absorbers... - GCNewsom 22:01:11 02/17/06 (1)
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.
- Re: On the subject of membrane absorbers... - Ethan Winer 08:51:59 02/18/06 (0)
  GC,
  You ask a lot of theoretical questions that I can't answer very well because I haven't tested all those combinations. If you have a specific problem at 54 Hz and want to build a panel trap, I'd use plywood 3/8 inch thick and calculate the cavity depth as needed.
  --Ethan
Re: question about how to put gypsyum boards - ponz45 16:41:31 02/16/06 (3)
thanks a lot for your reply,
what would you do in this situation? let' s suppose you have only gipsyum boards, mineral wood, and some piramidal pannels to correct your room: how woud you do? You simply would let the gypsium board parallel to the original concreet wall or is there any trick that could help, in getting the best possible resoult? have you got any suggestion?
i really would apriciate a lot if you could help me...i have been searching the net and reading books, but i really couldn' t find any usefull solution for my problem...i know...small budget is the real problem....but for the moment i can' t do nothing about it!
Anyone?
Thanks again,
ponz45
- Re: question about how to put gypsyum boards - Ethan Winer 15:00:13 02/17/06 (2)
  Ponz,
  > let' s suppose you have only gipsyum boards, mineral wood, and some piramidal pannels to correct your room: how woud you do? <
  That's like asking, "I have only a bicycle and I need to visit my aunt 50 miles away and be there in an hour. How would you do it?"
  Sorry, but the materials you described are just not up to the task.
  --Ethan
  - Re: question about how to put gypsyum boards - ponz45 16:41:57 02/17/06 (1)
    thanks again Ethan,
    I think I ' ve got the point...
    sorry to bother you again,
    you say the materials I described are not up to the task: what would you use instead?
    ponz45
    - Re: question about how to put gypsyum boards - Ethan Winer 08:53:37 02/18/06 (0)
      Ponz,
      > what would you use instead? <
      High density rigid fiberglass four inches thick straddling as many corners as possible, including the wall-ceiling corners.
      --Ethan

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