Patent GB-1513784-A (GB)
Title: Piezoelectric speaker system
IPC: H04R17/00
Filed: 1975-05-12
Abstract: 1513784 Piezoelectric loudspeakers PIONEER ELECTRONIC CORP 12 May 1975 [10 May 1974] 19814/75 Heading H4J A piezoelectric speaker system comprises a cylindrical substructure assembly 1 (Figs. 1, 2), a cylindrical piezoelectric film diaphragm 2 held under tension around the substructure assembly 1 and a plurality of pairs of electrodes on the diaphragm, electrodes of a pair covering the same part of the diaphragm but being on opposite sides to form vibration regions 9A, 9B (Figs. 5, 6) of number equal to the number of pairs. The substructure assembly 1 has a pair of circular base plates 3, 4 separated by a perforated cylinder 5 packed with glass wool or other sound absorbent. The cylinder 5 has felts providing partitions 8 either as shown or parallel with the cylinder axis. The diaphragm 2 is held in tension around a resilient member 7 covering the cylinders. The diaphragm 2 is a thin film of high molecular weight polymer material treated to exhibit the piezoelectric effect (e.g. polyvinylidene fluoride, polyvinyl fluoride, polyvinyl chloride, nylon-11 or polypeptide). Holders 10, 11 (Figs 5, 6) are attached to the ends of the diaphragm 2 and these engage in a slot S in the substructure assembly 1. The diaphragm 2 is provided with two electrodes on each side to define vibration regions 9A, 9B (Fig. 5). Printed conductors 13, 14 separated by a groove or insulator 12 are connected to the inner and outer electrodes of region 9A while printed conductors 17, 18 separated by a groove or insulator 16 are connected to the inner and outer electrodes of region 9B. If desired a plurality of film members with one or more vibration regions may be fitted around the substructure assembly 1 to form a single cylindrical diaphragm. Input signals of different phases and levels may be applied to the vibration regions 9A and 9B using a tapped transformer 21 and a selector switch SW3. The transformer 21 has secondary windings 21A, 21B and winding 21A has a centre tap as well as other taps, the centre tap being connected to switch contact S7 and the other taps to switch contacts S 1 to S6 and S8 to S13. When the movable contact S0 of switch SW3 is connected to fixed contact S1 the signal voltage applied to the region 9A is of the same phase and level as the signal voltage applied to the region 9B and non-directional characteristic is obtained. When the movable contact S0 is switched to fixed contact S7 for the centre tap the signal voltage applied to region 9B is zero and only the region 9A is energized to present a substantially unidirectional characteristic. When the movable contact S0 is switched to fixed contact S13 signal voltages applied to the regions 9A and 9B are of the same level but opposite phase to present a figureof-eight characteristic. Contacts S2 to S6 provide for varying the level of the signal voltages to the electrodes while keeping the signals in phase and contacts S8 to S12 provide different levels of the signal voltage in opposite phase. The various characteristics are illustrated (Figs. 7, 8, not shown). In a simplified arrangement (Fig. 3, not shown) the transformer 21 is dispensed with and two ganged switches (SW1, SW2) each having three fixed terminals connect the diaphragm electrodes to a source to provide a non-directional characteristic, a figure-of-eight characteristic or a substantially unidirectional characteristic, as desired. A further embodiment (Fig. 6) has a selector switch SW4 arranged to be selectively connected to either the collector or the emitter of a transistor Tr. A signal system A is connected to electrodes of region 9A through an amplifier 22A and a signal system B is connected to electrodes of region 9B through a variable resistor 23 and an amplifier 22B. Signals applied to the regions 9A and 9B are of the same phase when the switch SW4 connects to contact a and of opposite phase when the selector switch SW4 connects to contact b. The level of the signal voltage may be varied by adjusting resistor 23.