Paul,
I looked into this when I was considering an open baffle woofer for my Bassillas. Normally you look for a woofer with a Qt from 0.5 to 1.0. I think the Goldwood 18" woofers Roscoe used on his baffles a while back were at the upper end of this range. These have a response rise at the resonance frequency that helps compensate for the 6dB/octave baffle rolloff and extend the bass response. However with an active system, or passively if you are using a very efficient 15in driver (or two) you can do this with a bass lift filter network and a more highly damped driver. It will require more amplifier power though.
This is just a broad brush. You can find some good information from designs by Olsher, Pass, Linkwitz, and others on open baffles (or H-bins, slot loaded, all variants that extend the baffle size by folding).
|