ABSTRACT
Impedance matching by tubes and ducts was discussed in Chapter 7. Ducts are common in electroacoustics; they can be found in various types of delay lines and transmission line loudspeaker cabinets. The term transmission line is usually used for those loudspeaker enclosures where the duct is at least a quarter of a wavelength long at the lowest operating frequency of the loudspeaker system. Many loudspeaker designs use transmission lines that behave like open or closed tubes or ducts, with the driver mounted at one end generating a plane wave through the duct. Horns may be considered tapered ducts.
