Type of speaker enclosure which uses a port to increase bass output for a given power input resulting in 2 to 3 dB (decibels) more sound pressure than a similar sealed enclosure (also known as an acoustic suspension enclosure). A port is a specifically tuned circular opening in the enclosure itself with a round tube extending back into the box. The port allows audio output generated from the back-side of a speaker driver to be used (as a speaker driver moves in and out to generate sound waves the front of the driver creates the primary sound energy heard, however, the unseen rear side of the speaker also moves air and produces sound waves). The port allows air inside the enclosure to move to the outside of the enclosure in order to improve bass output. properly ported enclosure allows a speaker driver to perform more efficiently and provide more bass impact for a given input level compared to the same enclosure without a port. Many subwoofers use bass reflex enclosures as do many floorstanding and bookshelf speakers to achieve more bass for a given input power. While a ported bass reflex enclosure is more efficient and able to produce more bass output than a sealed enclosure, a ported enclosure generally does not have quite as high a level of articulation and detail. It may be slightly more boomy (lots of bass with poor definition) and less defined than a non-ported enclosure. Additionally, a sealed enclosure is able to play lower in the frequency spectrum compared to a ported or bass reflex enclosure (but not louder for a given input).