Type of speaker enclosure in which the back-force of a bass driver (the acoustic energy generated from the backside of the driver) is routed through a fairly long, winding channel or “hall” before being ported to the outside of the cabinet. By passing the sound waves through this maze inside the cabinet, it is reinforced and results in more impact than a simple ported enclosure, at least in theory. ransmission line enclosures must be very carefully tuned and built to exacting specifications. The distance the back-force sound wave travels is very specific based on some fraction of the wavelength of the speaker driver’s resonant frequency. Also speakers have a tendency to vibrate or resonate at a particular frequency. If a woofer used in a transmission line enclosure had a resonating frequency of 40 Hz, the wavelength would be about 28 feet. The internal sound channel inside the transmission line enclosure must be one quarter, one half or one-third this wavelength resulting in a channel length of 7, 14 or 21 feet respectively. f the enclosure is not created properly with the proper channel length, the transmission line design will not operate correctly. Transmission line enclosures are not often used in home audio with a few notable exceptions. They generally require large cabinets to fit the winding bass channel even with the channel folded on its self multiple times. Additionally, the cabinets are difficult to construct and the results are poor if not properly done. Most woofer cabinets instead use sealed or ported enclosures.