18[-inch] vented box" giving "four times the output with half the number of drivers". The Cerwin-Vega JE-36C has a five feet long folded horn chamber length in the wooden cabinet. Manifold subwoofers have two or more subwoofer speakers that feed the throat of a single horn. This increases SPL for the subwoofer, at the cost of increased distortion. EV has a manifold speaker cabinet in which four drivers are mounted as close together as practical. This is a different design than the "multiple drivers in one throat" approach. An unusual example of manifold subwoofer design is the Thomas Mundorf (TM) approach of having four subwoofers facing each other and sitting close together, which is used for theatre in the round shows, where the audience surrounds the performers in a big circle (e.g., Metallica has used this in some concerts). The TM approach produces an omnidirectional bass sound. Cerwin-Vega defines a manifold enclosure as one in which "...the driver faces into a tuned ported cavity. You hear sound directly from the back of the driver in addition to the sound that emanates out of the port. This type of enclosure design extends the frequency capability of the driver lower than it would reproduce by itself." Bandpass subwoofers have a sealed cabinet within another cabinet, with the "outer" cabinet typically having a vent or port. Bass instrument amplification In rare cases, sound reinforcement subwoofer enclosures are also used for bass instrument amplification by electric bass players and synth bass players. For most bands and most small- to mid-size venues (e.g., nightclubs and bars), standard bass guitar speaker enclosures or keyboard amplifiers will provide sufficient sound pressure levels for onstage monitoring. Since a regular electric bass has a low "E" (41 Hz) as its lowest note, most standard bass guitar cabinets are only designed with a range that goes down to about 40 Hz. However, in some cases, performers wish to have extended sub-bass response that is not available from standard instrument speaker enclosures, so they use subwoofer cabinets. Just as some electric guitarists add huge stacks of guitar cabinets mainly for show, some bassists will add immense subwoofer cabinets with 18-inch woofers mainly for show, and the extension subwoofer cabinets will be operated at a lower volume than the main bass cabinets. Bass guitar players who may use subwoofer cabinets include performers who play with extended range basses that include a low