Patent GB-324115-A (GB)
Title: Improvements in or relating to the distribution of reproduced sound
IPC: H04R3/12
Filed: 1928-10-19
Abstract: 324,115. Morison, G. E. Oct. 19, 1928. Loud-speakers; microphones; supporting; systems for transmitting music &c.-Relates to the distribution of sound from loud-speakers used in halls, theatres, cinemas or in connection with open air meetings. According to the invention, one or more loud-speakers is or are mounted on a continuously rotating support or alternatively the intensity of sound emitted by a number of fixed loud-speakers is continuously changed in such a manner as to produce the effect of a source which is continuously changing position. By replacing the loud-speakers by microphones, the arrangements can be employed for recording sound. In the construction, Fig. 1, a single moving coil loud-speaker 1 is mounted on a rotary support 2 driven by an electric motor 3, current being led to the driving coil 4 and magnetizing coil 5 through slip rings 6. A number of such units may be employed, in which case they may have a phase difference in their rotation, and/or a difference in rate of rotation, or they may be held in synchronism, as by a common drive. In a modification (Fig. 2, not shown) a number of loud-speakers are mounted on arms on a common horizontal shaft rotated by an electric motor, the reproducers moving in a fixed plane, which may, for example, be adjacent to the plane of a moving picture screen. The rotation of the sources in this manner provides the effect of an infinite number of fixed sound sources arranged in the path of the moving units and has thus the effect of a hypothetical source of large area having its centre more or less at the centre of the rotating shaft. Fig. 3 shows a further modification employing a number of fixed loud-speakers 9a - - 9<d> having their magnetizing coils energized from a battery 11 and their driving coils 12 connected across the output terminals of an amplifier 13 through two rotary potentiometers driven by an electric motor. The potentiometers are arranged to divide the output from the amplifier between the loud-speakers in such a manner that whilst the total effective impedance across the output terminals of the amplifier and the total sound intensity remains constant, the intensity of the sound emitted by the several loud-speakers is periodically increased and diminished in a cyclic manner. The two' similar constant impedance potentiometers shown have similar arms 14, 14<a> connected to a common shaft 14<c>, the arm 14 controlling the output of the units 9<a>, 9<b> whilst the arm 14a controls that of the units 9<c>, 9<d>, the two arms being arranged to have an angular displacement with respect to one another. If desired, one constant impedance potentiometer may be provided for each loud-speaker in which case the impedance balance is maintained by inserting an artificial impedance, equivalent to that of a sound reproducing unit in circuit with one arc of the potentiometer. Control of reverberation may be effected by varying the speed of rotation of the shafts. The Provisional Specification describes an arrangement whereby the output of each of a number of fixed loud-speakers is caused to vary by means of variable baffles and/or acoustic filters applied to each instrument.