GB529233A - Improvements in apparatus for conversion of wave motion into electrical energy and the converse - Google Patents

Abstract

529,233. Telephone instruments. TENNANT, W. J. (Shure, S. N., and Shure, F. (trading as Shure Bros.)). Jan. 3, 1939, No. 213. [Class 40 (iv)] A microphone is provided with an inlet leading to one side of a diaphragm or like member and between this inlet and the diaphragm is a system of chambers &c., the acoustic properties of which are such as to shift the phase of the sound wave pressure by an amount equal to the difference of phase between the pressures at the inlet and the other face of the diaphragm. This is stated to confer directional properties on the microphone, a theoretical discussion being given. Three examples are described. Fig. 3 shows a diaphragm 22 connected by a rod 25 to a piezo-electric crystal 2 in a chamber 28. A permeable partition 26 is arranged in front of the diaphragm 22. The chamber 28 is closed by a cover 29 leaving a narrow passage 31, the width of which can be adjusted by screws 41 and springs 42. In a modification the cover 29 is replaced by a permeable sheet. Fig. 10 shows a diaphragm 52 carrying a coil 53 which moves in the air gap of an annular magnet 56. The magnet 56 and diaphragm 52 define a chamber the inlet to which is formed by the air gap. This chamber is divided into two communicating parts by a disc 59 mounted at a short distance from the pole piece of the magnet. Figs. 13 and 16 show a corrugated rubber 100 vibrating between the pole pieces of a magnet. A chamber is formed by a plate 104 mounted a short distance behind the magnet pole pieces and to this chamber is attached a tube 109 filled with sound - absorbing materials such as wool.