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Re: Addendum on sealing and fibreglass density

Posted by David Aiken (A) on February 5, 2004 at 22:32:46

In Reply to: Re: Addendum on sealing and fibreglass density posted by Ethan Winer on February 5, 2004 at 08:54:30:

Jon's instructions call for the fibreglass batts to be compressed to a density of 2 lbs/cu ft. I don't know where that stands in relation to 703 and 705.

I use a version of Jon's quick and dirty traps built from polyester and polyester/wool blend insulation batts because I didn't want to use fibreglass (i used to work in the occupational health and safety field and have some reservations about the stuff). I originally tried them in the bags they came in, which was a little less than 2 lbs/cu ft density, and that worked ok though I felt things got better when I built wire mesh cages and compressed them to Jon's recommended density.

A few months ago, I rebuilt them making them a little smaller and using the saved batts along with another bag to make another 2 traps so I could stack them floor to ceiling in the corners behind the speakers. As a matter of interest, I tried listening with the batts just stacked loosely in the corner - no compression other than that provided by their own weight. They had no effect on bass frequencies at all - they may as well not have been in the room. I haven't experimented with compression to greater densities. All I can say is that I find them effective ata 2 lb/cu ft density and I think it's reasonable to assume that density will also be effective with ASC style traps constructed from insulation batting.

I don't know if anyone has done any experimenting to find out what the optimum density and thickness of the wall layer in an ASC style trap should be. One would expect that ASC would have done something along those lines. I also wonder whether the optimum thickness and density varies depending on the trap's diameter/internal volume. I think it is possible that it may vary slightly.

My understanding is that Jon works designing speakers for Peavey, not in an acoustics lab. I seem to remember him saying he had run measurements on his traps in a test chamber of some sort, but I don't know that he has regular or easy access to one on an ongoing basis.

David Aiken

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