page_title: Transmission line loudspeaker
section_title: Invention and early use
hierarchical_section_title: Transmission line loudspeaker / History of transmission line loudspeakers / Invention and early use
caption_attribution_description: English: Typical "transmission line" audio speaker enclosure topology.
context_page_description: A transmission line loudspeaker is a loudspeaker enclosure design which uses the topology of an acoustic transmission line within the cabinet, compared to the simpler enclosures used by sealed or ported designs. Instead of reverberating in a fairly simple damped enclosure, sound from the back of the bass speaker is directed into a long damped pathway within the speaker enclosure, which allows far greater control and use of speaker energy and the resulting sound.
  Inside a transmission line loudspeaker is a pathway into which the sound is directed. The pathway is often covered with varying types and depths of absorbent material, and it may vary in size or taper, and may be open or closed at its far end. Used correctly, such a design ensures that undesired resonances and energies, which would otherwise cause undesirable auditory effects, are instead selectively absorbed or reduced due to the effects of the duct, or alternatively only emerge from the open end in phase with the sound radiated from the front of the driver, enhancing the output level at low frequencies.
context_section_description: The concept was innovated within acoustic enclosure design, and originally termed an "acoustical labyrinth", by acoustic engineer and later Director of Research Benjamin Olney, who developed the concept at the Stromberg-Carlson Telephone Co. in the early 1930s while studying the effect of enclosure shape and size on speaker output, including the effect of "extreme length in a box baffle". A patent was filed in 1934. The design was used in their console radios beginning in 1936. A loudspeaker enclosure based on the concept was proposed in October 1965 by Dr A.R. Bailey and A.H. Radford in Wireless World (p483-486) magazine. The article postulated that energy from the rear of a driver unit could be essentially absorbed, without damping the cone's motion or superimposing internal reflections and resonance, so Bailey and Radford reasoned that the rear wave could be channeled down a long pipe. If the acoustic energy was absorbed, it would not be available to excite resonances. A pipe of sufficient length could be tapered, and stuffed so that the energy loss was almost complete, minimizing output from the open end. No broad consensus on the ideal taper (expanding, uniform cross-section, or contracting) has been established.
caption: This image is actually an inverted folded horn. You can tell as the throat is larger than near the port opening. A true Transmission Line enclosure is the same width 'vent' throughout.
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