Synthesized four channel sound using phase modulation techniques

Claim 1

A sound reproduction system for operation with a source of audio frequency signals, including in combination: first means having said source as an input for producing audio signals at four outputs, said first means including means for producing stereophonically related right and left signals R and L, and means for combining said right and left signals R and L and producing four composite signals represented by R- Delta 1L, R+ Delta 2L, L+ Delta 3R and L- Delta 4R, respectively at the respective outputs of said first means, where Delta 1, Delta 2, Delta 3, and Delta 4 are predetermined proportionality factors having values ranging from 0 to 1; electroacoustic transducer means corresponding in number to said first means outputs and defining a listening area, each of said outputs being coupled to a corresponding transducer means, said electroacoustic transducer means defining the listening area including four loudspeakers in correspondence to said four outputs of said first means; second means for producing signals having subsonic frequencies; and third means connected between the outputs of said first means at which the signals R- Delta 1L and L - Delta 4R are produced and the corresponding electroacoustic transducer means, for phase modulating such signals by said subsonic frequency signals produced by said second means, said third means including two phase modulators, one of which being adapted to phase modulate the composite signal R- Delta 1L, the other being adapted to phase modulate the composite signal L- Delta 4R.