The frequency at which the box/port system resonates, known as the Helmholtz resonance, depends upon the effective length and cross sectional area of the duct, the internal volume of the enclosure, and the speed of sound in air. Another metaphor often used is to think of the air like a spring or rubber band. The air mass in this opening resonates with the 'springiness' of the air inside the enclosure in exactly the same fashion as the air in a bottle resonates when a current of air is directed across the opening. Unlike closed-box loudspeakers, which are nearly airtight, a bass reflex system has an opening called a port or vent cut into the cabinet, generally consisting of a pipe or duct (typically circular or rectangular cross section). Two inch port tube installed in the top of a Polk S10 speaker cabinet as part of a DIY audio project. Depending on the exact relationship between driver parameters, the enclosure volume (and filling if any), and the tube cross-section and length, the efficiency can be substantially improved over the performance of a similarly-sized sealed-box enclosure. The port generally consists of one or more tubes or pipes mounted in the front ( baffle) or rear face of the enclosure. The design approach enhances the reproduction of the lowest frequencies generated by the woofer or subwoofer.

This port enables the sound from the rear side of the diaphragm to increase the efficiency of the system at low frequencies as compared to a typical sealed- or closed-box loudspeaker or an infinite baffle mounting.Ī reflex port is the distinctive feature of this popular enclosure type. A bass reflex system (also known as a ported, vented box or reflex port) is a type of loudspeaker enclosure that uses a port (hole) or vent cut into the cabinet and a section of tubing or pipe affixed to the port.

Ported box calculator