A Bass-Reflex (or Bass Reflex) is a type of speaker cabinet design that uses a duct or opening (called a port or port) to reinforce low frequencies.

In a speaker cabinet, the loudspeaker moves back and forth. In a sealed cabinet, the sound energy produced by the backward movement of the cone is lost inside the cabinet.

In the bass-reflex design, the port is tuned so that the rear sound energy, at low frequencies, exits through it in phase with the energy from the front of the loudspeaker.

This combination of the two waves results in a reinforcement of the bass, increasing the efficiency and extension of the low frequencies of the speaker.

It is a very popular design because it allows smaller speakers to produce more powerful bass. The disadvantage is that, below the port's tuning frequency, the bass response decays much more abruptly than in a sealed box, which some consider a less "natural" sound.