Taget fra: http://www.beoworld.co.uk/:

The Ambiophonic Stereo Adaptor System produced an ambiophonic, or 'pseudo-surround' sound to your Bang & Olufsen passive loudspeaker system when used with separate rear speakers. In the mid 1970's there were quite a few of these units from various manufacturers available; Bang & Olufsen produced this non-powered unit to provide the same ambiophonic effect when you couldn't afford, or didn't want to afford, one of the quadraphonic music systems which were on sale.

Receivers and amplifiers with the 'ambio' function were products which, apart from stereo, could also reproduce the ambience or sound information of a room. Ambient information was included on most stereo vinyl recordings but could not be reproduced by a sound system with two loudspeakers or an ordinary stereo amplifier. Bang & Olufsen systems with the 'ambio' function had facilities which electronically subtracted the difference signal (i.e. the difference between left and right channels) which contained ambient information. This information was fed into two extra loudspeakers which were placed as side speakers in a room. Ambiophony was an extension of stereo reproduction and enhanced the sense of realism. It could be used with nearly all stereo programme materials.

Produced from 1974 - 78, the unit could be used with such stereo receivers as Beomaster 4400 which was Bang & Olufsen's last model to incorporate with ambiophonic circuitry.