A bass reflex duct is a component in loudspeaker systems that serves to amplify the bass range and increase the efficiency of the loudspeaker. The duct is usually a tubular opening in the loudspeaker cabinet, usually located at the rear or front of the cabinet.

The way the bass reflex duct works is based on the principle of resonance. The tube creates a resonant frequency that helps increase the sound pressure in the bass range and relieves the speaker. The result is a fuller, deeper bass that can be reproduced with less distortion.

The bass reflex duct works by moving air in and out of the speaker system enclosure. The air is moved through the opening in the duct, reducing the pressure in the cabinet. This allows the speaker to move more air and thus produce more bass.

The size, length and shape of the bass reflex duct can affect the performance of the speaker system. Careful matching of the duct to the characteristics of the speaker and enclosure is important to achieve the best possible performance.