Patent ID: 7072474

Claim:
A method of producing a sound recording for playing through a closely-spaced pair of loudspeakers defining with a predetermined listener position an included angle of between 6° and 20° inclusive, filter means being employed in creating said sound recording, the filter means having characteristics which are so chosen that when the sound recordings are played through such a closely-spaced pair of loudspeakers the need to provide a virtual imaging filter means at the inputs to the loudspeakers to create virtual sound sources is avoided, the sound recording being such that when played through the loudspeakers a phase difference between vibrations of the two loudspeakers results where the phase difference varies with frequency from low frequencies where the vibrations are substantially out of phase to high frequencies where the vibrations are in phase, the lowest frequency at which the vibrations are in phase being determined approximately by a ringing frequency, f 0 defined by f 0 =½τ where ⁢ ⁢ τ = r 2 - r 1 c 0 , and where r 2 and r 1 are the path lengths from one loudspeaker center to the respective ear positions of a listener at the listener position, and c 0 is the speed of sound, said ringing frequency f 0 being at least 5.4 kHz.