Bassreflex

Bassreflex, or bass-reflex enclosure, is a type of loudspeaker enclosure that uses a port or vent to improve low-frequency performance. The term typically describes vented (port) designs in which part of the speaker’s output is radiated through the port as well as through the driver.

Principle: The woofer works against a springy air mass inside the cabinet, and the port provides an acoustic resonance that reinforces bass output at a chosen tuning frequency. The port’s air mass and the enclosure’s air spring interact so energy is transferred from the driver to the port, increasing efficiency and extending bass relative to a similarly sized sealed box. The tuning is set by the cabinet volume, port cross-section, and port length; larger volume and different port dimensions change the tuning.

Design, variants, and sizing: Common configurations include one or more ports, rectangular or cylindrical boxes, and ports that can be round or slot-shaped. End corrections are applied to account for the port terminations. Flared ends or damped ports are sometimes used to reduce turbulence and noise. If a port is impractical, a passive radiator can be used to achieve a similar effect without an air vent.

Advantages and drawbacks: Bass-reflex enclosures typically provide higher low-frequency efficiency and deeper bass for a given box size than sealed designs. They can be more sensitive to precise tuning and enclosure tolerances, and may exhibit port noise, increased group delay, or uneven bass response if not well designed.

In practice, bass-reflex designs are common in consumer loudspeakers and subwoofers, chosen to maximize bass output within compact enclosures. See also: sealed box, passive radiator, Thiele-Small parameters.