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R/E/P => R/E/P Archives => Acoustics in Motion => Topic started by: Bill_Urick on December 09, 2007, 06:06:53 AM

Title: Bass Trap "membrane"
Post by: Bill_Urick on December 09, 2007, 06:06:53 AM

Last night I was checking out some bass traps in the drum room of a small local studio here in the ATL. They had 1/4" peg board behind the fibreglass. Good idea? How would that affect the response of the trap?

Title: Re: Bass Trap "membrane"
Post by: Ethan Winer on December 09, 2007, 12:52:36 PM

Nobody can say for sure without measuring those specific panels with and without the pegboard in a lab. In my experience, things like wood and Masonite reduce the effectiveness of absorbers at low frequencies. One exception might be if the peg board were in front of the fiberglass, to create a sort of Helmholtz trap. But it doesn't sound like this is what they're doing. I suggest you ask them if this is a home-made idea or if it was based on actual research.

--Ethan

Title: Re: Bass Trap "membrane"
Post by: rankus on December 09, 2007, 02:13:20 PM

What would you suggest as a good alternative membrane Ethan?  I am planning on trying to make some membrane traps to augment my broadband absorbers (and on a tight budget as always)

TIA

Title: Re: Bass Trap "membrane"
Post by: Bill_Urick on December 09, 2007, 09:40:19 PM

Ethan Winer wrote on Sun, 09 December 2007 12:52

Nobody can say for sure without measuring those specific panels with and without the pegboard in a lab. In my experience, things like wood and Masonite reduce the effectiveness of absorbers at low frequencies. One exception might be if the peg board were in front of the fiberglass, to create a sort of Helmholtz trap. But it doesn't sound like this is what they're doing. I suggest you ask them if this is a home-made idea or if it was based on actual research. --Ethan

Ethan, in this instance how do you define "low frequencies"?

Title: Re: Bass Trap "membrane"
Post by: jfrigo on December 10, 2007, 12:49:35 PM

If it has holes, it's not acting as a membrane, rather a resonant absorber (assuming a sealed cavity behind). The hole density in off-the-shelf peg board is typically too great to be very effective at low frequencies. I'd have to measure and run the numbers for the specific case, but I'm thinking mid to upper hundreds which takes it above what you'd typically call bass trapping.

Title: Re: Bass Trap "membrane"
Post by: Ethan Winer on December 10, 2007, 04:48:05 PM

Bill Urick wrote on Sun, 09 December 2007 21:40

Ethan, in this instance how do you define "low frequencies"?

I dunno, maybe below 100 to 200 Hz or so.

--Ethan

Title: Re: Bass Trap "membrane"
Post by: Ethan Winer on December 10, 2007, 04:49:12 PM

rankus wrote on Sun, 09 December 2007 14:13

What would you suggest as a good alternative membrane Ethan?

This will sound like a supermarket joke, but paper or plastic.

--Ethan

Title: Re: Bass Trap "membrane"
Post by: tom eaton on December 16, 2007, 06:22:55 PM

I have some RPG traps that have steel membranes.  Seriously.

http://www.rpginc.com/products/modexplate/modexp_img/Type-2- sm.gif

-t