GB1367705A - Audio reproduction systems - Google Patents

Abstract

1367705 Four channel stereophonic systems DYNACO Inc 23 Aug 1971 [10 June 1971] 39514/71 Heading H4R In a four or more loud-speaker, two amplifier, stereophonic system in which two loud-speakers, arranged one each side at the front of a listening area, are fed with signals from the respective amplifiers, or the signal from the respective amplifier combined with a fraction of the signal from the other amplifier, the two loud-speakers arranged one each side at the rear of a listening area are each supplied with a signal from the respective amplifier which has subtracted from it a fraction of the signal from the other amplifier. As shown in Fig. 1, front loud-speakers 21, 22 are fed from respective L and R signals from a stereophonic source 11. The rear speakers 23, 24, each have a first terminal connected to receive the respective L and R signals from the source and their second terminals interconnected by a resistance pad 28 which adds a portion, either 25 or 50%, of the other channel, in antiphase to the signal applied to their first terminal. In order to provide greater presence to the sound in the front of the listening areas a matrix (37, 38, 40), Fig. 2 (not shown), can be provided to positively blend the L and R signals at the input to the amplifiers 12 and 13. A similar effect is provided by a fifth loud-speaker (41) connected in place of resistor 29 in the rear speaker coupling network 28 and arranged in the centre front of the listening area, Fig. 3 (not shown), alternatively the fifth speaker could be arranged to give monophonic reproduction in a separate listening area, Fig. 4 (not shown). In place of the resistive combining network 28 of the arrangements described above auto transformer may be used to combine the signals. In auto transformer arrangements described, positive blending of signals in the front speakers and negative bending of speakers in the rear speakers is provided in the arrangement of Fig. 5 (not shown) while a system giving just negative blending of the signal, in rear speakers is described with respect to Fig. 6 (not shown). Also described in an arrangement, Fig. 8 (not shown), for deriving the L and R channel signals from microphones placed at the corners of the source hall. The outputs of the microphones are combined first to simulate microphones placed at the centres of the front, back, and sides, of the source hall and then matrixed to apply the four resulting signals on two channels L and R so that, on reproduction by apparatus according to Figs. 2 or 5, each loud-speaker reproduces signals arising predominantly from the corresponding microphone with some signal from the two adjacent microphones, and no signal arising from the diagonally opposite microphone. The matrixing may employ cross feed of 50%, or, to provide reduced signals from the rear speakers, a cross feed of less than 50%, preferably 26À8%.