A pair of three-way transmission-line speaker systems was designed, constructed, and tested for the purpose of providing a high-accuracy reference monitor capable of reproducing the full audio range with extremely low harmonic distortion and fast transient response with minimal coloration. Each of the speaker cabinets is a mirror image of the other; and edges are made rounded to minimize diffraction effects. The use of six mid-range drivers enclosed separately from the woofer in each of the extremely stiff cabinets ensure linear operation even at fairly high levels of power input. The tweeters, also enclosed separately, are arranged to provide wide dispersion. While a three-way crossover network is incorporated, separate input jacks allow for bypass in order to accommodate tri-amplified inputs. The transmission line provides a perfectly resistive termination to the woofers, functions as a low-pass filter and virtually eliminates cabinet resonance. Damping material varies in density, tapering off from 0.5 lb/ft[sup 3], where the last 30 cm of the transmission line is unfilled. Directivity through 180(degrees) proved be extremely even in the test ranges of 101 to 13 212 Hz.