Abstract: A bass reflex speaker system with a ducted port which can be made without coloration in the mid frequency band of the speaker caused by standing wave resonances in the duct. The system includes one or more openings in the wall of the duct between the ends of the duct, and covering the openings with a deflectable membrane, such as a film of latex-like material, or a rigid membrane with a flexible surround. The additional openings prevent pressure build-up at a quarter wavelength location of undesirable standing waves, and thereby cancels the standing waves, but they do not affect the operation of the duct at the Helmholtz frequency of the bass reflex system.