Tube of a specified length and diameter (length and diameter dependent on specific application) with one end open to the outside of a speaker enclosure through a round hole and the other open to the inside of the speaker enclosure. Ports are used primarily for subwoofers and other bass speaker drivers. They allow the air movement inside the speaker enclosure caused by the back of the speaker driver to vent or move to the outside. sing a port enables a speaker driver to play at a louder level than an equivalent speaker driver in a sealed enclosure when driven with the same power. Ported enclosures, also known as bass reflex enclosures, enhance the efficiency of a speaker driver, but they result in some decrease in total low frequency extension. As a compromise between ports and completely sealed enclosures, some speaker enclosures feature passive radiators allowing the cabinet to remain sealed while taking advantage of some energy generated inside the enclosure.