Calculate your opening aperture of the cavity for the desired bass response required Brother...an Let that air out OM...
Ah, yes! A device for sealing an aperture in the wall of a cavity including a tubular elastic membrane which extends from inside the cavity through the aperture to the exterior. A deformable cap closes the inner end of the tubular membrane. The membrane is radially tensioned, e.g., by an annular ring formed in the outer end of the tube to seal the membrane against the edges of the aperture.
Right?
(United States Patent 4809871)