ABSTRACT
If the subwoofer approach is applied to upscale music-listening rather than an audio-visual experience, it is normal not to take chances with the possibility of losing low-frequency stereo information, and two subwoofers are used, for left and right in the usual way. The subwoofers are often placed under the main speakers, or very close to them, to preserve what stereo cues can be extracted from their output. They are not placed almost at random in the listening room in the way that mono subwoofers often appear to be. A classic application of stereo subwoofers is the extension of the bass response of electrostatic loudspeakers, notably those by Quad, such as the ESL-57 introduced in 1955 and the later ESL-63.
