page_title: Bass reflex
section_title: History
hierarchical_section_title: Bass reflex / History
caption_attribution_description: English: Keesonic Kub; compact, two way, bass reflex loudspeaker designed by Peter Keeley and manufactured in the UK in the 1980s. Grille removed in this photo.
context_page_description: A bass reflex system is a type of loudspeaker enclosure that uses a port or vent cut into the cabinet and a section of tubing or pipe affixed to the port. 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.
  A reflex port is the distinctive feature of this popular enclosure type. The design approach enhances the reproduction of the lowest frequencies generated by the woofer or subwoofer. The port generally consists of one or more tubes or pipes mounted in the front or rear face of the enclosure. Depending on the exact relationship between driver parameters, the enclosure volume, and the tube cross-section and length, the efficiency can be substantially improved over the performance of a similarly sized sealed-box enclosure.
context_section_description: The effect of the various speaker parameters, enclosure sizes and port (and duct) dimensions on the performance of bass reflex systems was not well understood until the early 1960s. At that time, pioneering analyses by A.N. Thiele and Richard H. Small related these factors in a series of "alignments" (sets of the relevant speaker parameters) that produced useful, predictable responses. These made it possible for speaker manufacturers to design speakers to match various sizes of enclosures, and to match enclosures to given speakers with great predictability.  All of this is constrained by the laws of physics, which is covered in detail in Thiele and Small's work. It is not possible to have a small speaker in a small enclosure producing extended bass response at high efficiencies (i.e., requiring only a low-powered amplifier). It's possible to have two of these attributes, but not all; this has been termed Hofmann's Iron Law after J. Anton Hofmann of KLH's summary (with Henry Kloss) of Edgar Villchur work years earlier. The sound pressure produced depends upon the efficiency of the speaker, the mechanical or thermal power handling of the driver, the power input and the size of the driver.
caption: A small Keesonic Kub speaker. With the front grille removed, the port is visible between the two drivers.
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