GB1348643A - Loudspeakers - Google Patents

Abstract

1348643 Loud-speakers; surround sound EMI Ltd 28 Oct 1971 [29 Oct 1970] 51569/70 Headings H4J and H4R A loudspeaker for use in a surround sound system has two voice coils supported on a common former and operating on the same diaphragm such that, if the same signal is applied to each coil, the sound output due to one coil will be greater than that due to the other coil. The ratio of the impedances of the two voice coils is substantially 2À4 at 400 Hz. Thus the two coils may have different numbers of turns, e.g. in the ratio of about 1 : 0À04. A pseudo-quadraphonic system (Fig. 1) has four such loud-speakers 1, 2, 3, 4 at the four corners of a square and fed from the L and R channels of a single stereophonic two-channel amplifier. Fig. 2 shows the voice coils 5 and 6, 7 and 8, 9 and 10, 11 and 12 (see Fig. 1) connected to the stereophonic amplifier via R terminals 13, 14 and L terminals 15, 16. The coils of the front loud-speakers 1, 4 act in an additive sense while the coils of the rear loudspeakers 2, 3 act in a subtractive sense. For this purpose, coils 8 and 9 are wound in the opposite sense to the other coils. Alternatively all the coils are wound in the same sense but the connections to coils 8 and 9 are reversed (Fig. 3, not shown). The loud-speakers are then identical. The signals applied to the loudspeakers are:- Loud-speaker 1, 0À707R + 0À293L, i.e. R + 0À41L Loud-speaker 2, 0À707R - 0À293L, i.e. R - 0À41L Loud-speaker 3, 0À707L - 0À293R, i.e. L - 0À41R Loud-speaker 4, 0À707L + 0À293R, i.e. L + 0À41R For an amplifier impedance of 8 ohms, the impedances of the two types of coil are 0À707 x 16=11À32 ohms and 0À293 Î 16=4À68 ohms. In another arrangement (not shown) the two coils wound on each loud-speaker are in the opposite sense. The larger impedance coils are all wound in the same sense as each other and the smaller impedance coils are all wound in the same sense as each other. In yet another arrangement (Fig. 4, not shown) four loudspeaker systems (21, 22, 23, 24) each consisting of two loud-speaker units connected in parallel are used. In this arrangement the signals applied to each loud-speaker unit are as previously described but the circuit (e.g. that of Fig. 2) is such that two identical coils in parallel replace each individual coil.