Bass reflex loudspeaker has acoustic leakage in walls of port duct

摘要

The bass reflex loudspeaker has a port tube 100 with an acoustic leakage path through a motile or moveable part thereof which is frequency-dependent. The tube walls may expand and contract (fig 3). The motile part may comprise a felt wall 110 or a corrugated wall (fig 5) or a diaphragm over a hole in the tube wall. At relatively low frequencies (corresponding to Helmholtz resonance), the leakage path has a relatively high acoustic impedance; at relatively high frequencies (corresponding to longitudinal resonances), the leakage path has a relatively low acoustic impedance. In this way longitudinal tube resonances are damped as their energy at higher frequencies is radiated transversely through the port tube walls rather than contributing to the output of the loudspeaker itself.