A British-developed surround sound system designed to reproduce a true three-dimensional sound field. Based on the late Michael Gerzon’s (1945-1996; Oxford University) famous theoretical foundations, Ambisonics delivers what the ill-fated quadraphonics of the ’70s promised but couldn’t accomplish. Requiring two or more transmission channels (encoded inputs) and four or more decoded output loudspeakers, it’s not a simple system; nor is the problem of reproducing 3-dimensional sound. Yet with only an encoded stereo input pair and just four decoded reproducing channels, Ambisonics accurately reproduces a complete 360-degree horizontal sound field around the listener. With the addition of more input channels and more reproducing loudspeakers, it can develop a true spherical listening shell. As good as some think it is, a mass market for Ambisonics has never developed due to several factors. First, the actual recording requires a special tetrahedron array of four microphones: three to measure left-right, front-back and up-down sound pressure levels, while the fourth measures the overall pressure level. All these microphones must occupy the same point in space as much as possible. So far, only one manufacturer (first Calrec, bought by AMS, bought by Siemens, sold, now Soundfield Research) is known to make such an array. Next, a professional Ambisonics encoding unit is required to matrix these four mic signals together to form two or more channels before mastering or broadcast begins. And finally, the consumer must have an Ambisonics decoder, in addition to at least four channels of playback equipment.