Originally Posted by Roger Dressler
I've seen tons of posts about superchunks and the like. Is there a similarly simple design for DIY pressure type bass traps in soffits or corners?
Dennis is technically right. However if the bass trap is deep enough, as in straddling a corner, it can catch enough of the velocity wave at low frequencies (1/10 of a wavelength, for example) to be effective.
There is also the technique of converting a velocity absorber to a pressure absorber. A membrane or thin panel attached to the front of a porous absorber does exactly this. Sound pushes against the membrane, the membrane moves, and now there is air motion for the velocity-type absorber to directly work on.
Membranes absorbers can be tricky, though. If the membrane has too much mass, it creates a tuned mass-air resonance which only works over a limited range of frequencies. The bass trap has a "Q" which can be high and therefore very effective, but which may not be tuned to the frequencies you need.
Fortunately, the process of moving from pure velocity absorber to a tuned pressure absorber is a continuous one. Using a small amount of mass, say, from the paper facing which comes attached to ASJ or FRK type fiberglass, results in an absorber with a very broad and bass-extended frequency range. 1/8 inch of mass-loaded vinyl, however, would create an absorber tuned to a pretty specific and limited range of frequencies. The latter is what is found in a product such as the RPG Modex Corner Bass Trap.