Patent GB-440330-A (GB)
Title: Improvements in piezo-electric devices for converting electrical oscillations into mechanical vibrations
IPC: H04R17/00
Filed: 1934-05-23
Abstract: 440,330. Deaf-aids; loud-speakers ; receivers ; phonographic recorders. SONOTONE CORPORATION, 19, West 44th Street, New York, U.S.A. May 23, 1934, No. 15458. Convention date, May 24, 1933. [Class 40 (iv)] [See also Group XL] A device responsive to electrical oscillatory energy for imparting mechanical vibrations to a vibratory load, more particularly for use in connection with boneconduction hearing aid devices,loud-speakers,telephone receivers and phonographic recorders, comprises a piezoelectrically driven vibratory member and means for coupling the vibratory load to a portion of said vibratory member which portion vibrates with a relatively small amplitude and is subjected to vibratory forces exerted by at least one freely projecting portion of said vibratory member vibrating with relatively large amplitude for imparting vibratory energy produced by said freely projecting vibratory member portion to said load. The piezo - electric body may consist of a pair of superposed bars of Rochelle salt clamped at one end about which they are adapted to bend under the influence of an applied electric field or a pair of superposed rectangular plates clamped at one corner and adapted to twist under the influence of an electric field. Weights may be attached to the freely oscillating end or corners. Piezoelectric bodies comprising four, six or more crystal layers are also described whilst, according to a further modification, a single crystal strip may have its surface united to a metal strip. Fig. 6 shows a construction of bone conduction hearing aid device comprising a piezo-electric crystal unit 56 consisting of two superposed crystal strips carrying outer electrode sheets 59, 60 and an intermediate electrode sheet 63. The lower end of the unit 56 is clamped by an insulating block 57 against a pair of metal blocks, one of which is shown at 53, fibre layers 55 being interposed as shown. The metal blocks are insulated from each other and one is connected by contact strips to the outer electrodes 59, 60 whilst the other is connected by a contact strip to the intermediate electrode 63. Plug pins 67 carrying the leading-in cord 68 are received in holes 66 in the metal blocks. A clamp 70 carrying the contact button 77, which projects through an opening 78 in the front wall 51 of the enclosing casing 50, is secured around the unit 56 at a short distance above the clamped lower end thereof whilst a lead weight 84 is fitted over and attached to the upper free end of the unit. The rear of the casing is closed by a two layer cover member 90, 91 having a channel 92 therebetween for receiving one end 93 of a head band 94. Fig. 10 is a circuit diagram showing a transmitting microphone 96 connected to the hearing aid device 56 through an amplifier 98 and battery 99, a variable resistance 100 and a transformer 101. Modifications are described in which the cone of a loud-speaker, the diaphragm of a telephone receiver and the cutter of a phonographic recorder are coupled to a crystal unit similar in construction and arrangement to that shown in Fig. 6, at a short distance from the clamped end thereof. Further constructions of loudspeakers and phonographic recorders employing a crystal unit consisting of a pair of superposed rectangular plates clamped at one corner and adapted to twist under the influence of an electric field are also described, the cone or cutter being coupled to the plates at a point adjacent to the clamped corner. In these constructions weights may be attached to all the free corners of the plates.