US Patent 8180075 Arrangement for variable bass reflex cavities

A modified housing in a portable product (400, 500, 700, or 800) includes a housing detail (405, 506, 706 or 710 or 806) forming at least a portion of a loud speaker back cavity having a pipe inner diameter for a resonant pipe (408, 508, 708, or 808), and a modification to the housing detail altering a cross section area of the pipe inner diameter to compensate for changes to a loud speaker back cavity volume. The housing detail can include a battery door (404, 504, 704) for the portable product that forms at least one side of the resonant pipe. The battery door can define the loud speaker back cavity volume and further fills at least part of the resonant pipe in a manner that maintains the loud speaker back cavity volume and the cross sectional area of the pipe inner diameter at a predetermined ratio.