GB1382927A - Electroacoustic transducer - Google Patents

Abstract

1382927 Electroacoustic transducers INTERNATIONAL BUSINESS MACHINES CORP 1 June 1973 [30 June 1972] 26209/73 Heading H4J An electroacoustic transducer for decoding a digital signal received serially by code word and converting it to sound comprises a sound generating element and a plurality of driving elements therefor. Each driving element can be energized independently of the others by an electrical signal whose magnitudes is determined for each code word by the value of the digital signal in a respective bit position thereof. A cantilevered piezoelectric bender plate (Fig. 1) is controlled by coded PCM signals and directly converts them to sound waves. The plate consists of two layers of ceramic material. At least the upper one has piezoelectric properties. A common electrode is located between the two layers. Six rectangular bit electrodes with different areas are mounted side-by-side as driving electrodes and each is connected to a respective electric line corresponding to a different bit position of the coded PCM signals. The deflections caused by the bit electrodes when energized with equal signals have the same ratio as the positional weights in a binary code, i.e. 1 : 2 : 4 : 8 : 16 : 32. If several bit electrodes are energized simultaneously, the deflections are added together. Binary signals with any other positional weights can be used if the electrodes are suitably dimensioned, as can digital signals other than binary signals. Instead of ceramic piezoelectric layers, monocrystalline layers can be used. A relatively broad and short bender plate (Fig. 3, not shown) may be used with four electrodes (1<SP>1</SP> to 4<SP>1</SP>) mounted in pairs across the width of the plate. An alternative device for binary signals with a sign bit is similar to that of Fig. 1 but the bender plate consists of two oppositely polarized ceramic or crystalline piezoelectric layers with a common electrode mounted in between (Fig. 4, not shown). Two similar sets of bit electrodes are mounted on the surfaces of the bender plate. In another arrangement a circular plate of piezoelectric material consists of two layers with a common electrode in between. Bit electrodes (1c, 2c, 3c ... 6c), Fig. 5 (not shown), have the form of concentric rings. The circular plate acts as the diaphragm. It may form part of an earphone capsule (Fig. 6, not shown). Another arrangement uses an electrostatic transducer (Fig. 7, not shown) comprising an elastically suspended metal diaphragm spaced from bit electrodes in the form of concentric rings. An electromagnetic transducer (not shown) has the coil of an electromagnet subdivided into a plurality of windings. The number of turns for any one winding is such that the effected deflection of the diaphragm is proportional to the positional weight of the respective code bit.