Here's some interesting reading :

http://www.ethanwiner.com/acoustics.html

Owens-Corning 703 rigid fiberglass seems to be pretty absorbent at 250 Hz; might be the best option. Comes in 2'x4' panels, 1" thick...

Last edited by bridgman; 01/26/06 05:15 AM.
M60ti, VP180, QS8, M2ti, EP500, PC-Plus 20-39
M5HP, M40ti, Sierra-1
LFR1100 active, ADA1500-4 and -8