sentences:  Bass traps typically combine structural mechanisms that can work at both positions of high particle velocity/low pressure (thick fiberglass) and high pressure/low particle velocity (membranes).Porous bass trap absorbers need to be very thick to be effective at lower frequencies so they tend to be allocated either as diagonal wedges in the corners or as thick rectangular bulk behind false walls where they are out of the way and less likely to disrupt higher frequencies or room function.Air gap behind a porous panel absorber e.g.