Multi-channel decoding circuit for two-channel audio systems

Claim 2

A passive bridging circuit for producing additional powered channels of audio information from the speaker outputs of the left and right channels of a stereo amplifier comprising: a. a pair of loudspeakers each having a positive and negative terminal for connecting to an audio source; b. left and right channel transformers having primaries and secondaries, the primaries being connected to the said stereo amplifiers's left and right speaker position and negative outputs respectively, the loudspeakers coupling the secondaries of the two transformers, one loudspeaker between the two plus terminals of the secondaries and the other loudspeaker between the two minus terminals, and c. resistive means connecting the primaries of said transformers to one of said speaker terminals for coupling in-phase information to said speakers to obtain back separation, whereby said loudspeakers are coupled across the left and right channels of said amplifier to reproduce sound corresponding to the difference between the left and right signals from the amplifier.

Claim 3

A passive bridging circuit producing two additional powered channels of audio information from the speaker outputs of the left and right channels of a stereo amplifier comprising: a. left and right channel speakers having positive and negative terminals for connection to an audio source; and b. left and right channel transformers each having primary and secondary windings, the left transformer primary being connected across said left channel output, the right transformer primary being connected across said right channel output, the positive side of the left transformer secondary being connected to one terminal of said left speaker, the positive side of the right transformer secondary being connected to one terminal of the right speaker, the remaining speaker terminals being connected to the positive terminal of the opposite channel output, the negative side of the transformer secondaries being connected to one side of its own primary winding whereby the primary to secondary ratio determines the ratio of the mixture from each channel produced by said speakers and the phase of the secondary voltage determines the phase of the signals produced by said speakers.

Claim 4

A passive bridging circuit producing two additional powered channels of audio information from the speaker outputs of the left and right channels of a stereo amplifier comprising: a. left and right channel speakers having positive and negative terminals for connection to an audio source; and b. left and right channel transformers each having primary and secondary windings, the left transformer primary being connected across said left channel output, the right transformer primary being connected across said right channel output, the positive side of the left transformer secondary being connected to one terminal of said left speaker, the positive side of the right transformer secondary being connected to one terminal of the right speaker, the remaining speaker terminals being connected to the positive terminal of the opposite channel output, the negative side of the transformer secondaries being connected to one side of its own primary winding whereby the primary to secondary ratio determines the ratio of the mixture from each channel produced by said speakers and the phase of the secondary voltage determines the phase of the signals produced by said speakers.

Claim 5

A circuit according to claim 2 wherein the positive side of the transformer primaries are connected to the amplifier channels through a capacitive impedance to produce a phase shift over a substantial portion of the audio frequency range whereby desirable back separation and phase compensation is obtained for quadraphonically recorded materials.

Claim 6

A circuit according to claim 3 wherein a variable impedance is added to the circuit to control the total power available to said speakers.

Claim 7

A circuit according to claim 4 further including ganged switching means for connecting the negative side of both transformer secondaries to either the positive or negative sides of their corresponding transformer primaries.

Claim 8

The circuit according to claim 3 wherein said capacitive impedance includes a capacitor having a swamping resistor connected thereacross.

Claim 9

A circuit according to claim 2 wherein said transformers having a primary to secondary step-up ratio, said secondaries being in-phase with the primaries, whereby each loudspeaker responds more strongly to the out of phase signals from the amplifier channel coupled through the transformers than to the direct coupled channel.