Acoustic Transmission Line

An acoustic transmission line is the acoustic analog of the electrical transmission line, typically thought of as a rigid-walled tube that is long and thin relative to the wavelength of sound present in it. The now mostly obsolete speaking tube served to transmit sounds to a remote location with minimal loss and distortion, as a simple coaxial cable or waveguide does for electrical signals. Musical wind instruments such as pipe organs, woodwinds and brass instruments can be also be modeled in part as transmission lines, though their job also includes generating the sound, controlling its spectrum, and coupling it efficiently to the open air, functions analogous to those of electronic oscillators, filters and antennas.

In particular, "transmission line" is the name of a specific audio speaker enclosure topology, in which sound from the back of the bass speaker chassis passes along a long (generally convoluted) path within the speaker enclosure. The energy is absorbed on this path, or emerges from the open end in phase with the sound radiated from the front of the driver, enhancing the output level at low frequencies.