The two midrange drivers and tweeter, arranged as an MTM (D’Appolito) array, are housed in the top cabinet which is faceted to reduce diffraction effects.
The bass driver occupies the lower cabinet and is reflex loaded via a large forward- ring port.
The WM-4 combines wide bandwidth (30Hz- 30kHz) with high sensitivity (90dB) but is easy to drive, with an average impedance of around 6 ohms and low impedance phase angles. To make the WM-4 better adapted to use with some valve amplifiers, an optional impedance smoother is provided which reduces the impedance variation and hence the frequency response errors that result from high amplifier output impedance.
The WM-4 is a loudspeaker with two great abilities: it is capable of revealing the smallest change in the partnering system and thus is a wonderful analytical tool. However and very unusually for an analytical tool it is capable of kicking back and playing music of any era and making it enjoyable, involving and communicative.
The two abilities are rarely found together in loudspeakers designs but the wide dynamic range and very low distortion of the WM-4 deliver performance at the highest level.