Gear & technology
Bass reflex
Also called ported speaker, vented enclosure, ported enclosure
A bass reflex speaker has a port, a tube or slot in the cabinet, tuned so the air inside resonates and reinforces the bass near the speaker’s low-frequency limit. It is the most common enclosure because it gets more bass from a given box.
The port uses the driver’s rear wave, which a sealed enclosure throws away, to add output over about an octave around the tuning frequency. Below that, output falls away steeply. The design is efficient, which is why most bookshelf and floorstanding speakers, and many subwoofers, are ported.
The cost is control: the bass around the port tuning can sound less tight than a sealed design, the port can "chuff" at high levels, and the steep roll-off below tuning is less forgiving of placement near walls. A Passive radiator does the same job as a port without the airflow.