GB601629A - Improvements in or relating to mechanical vibratory devices - Google Patents

Abstract

601,629. Electro acoustic transducers. STEVENS, A. H. (Brush Development Co.). Sept. 27, 1945, No. 25076. [Class 40 (iv)] In an electro-acoustic translation device, such as a microphone, in which the vibratile element has a resonance frequency, substantial damping is effected at the said resonance frequency by means of an acoustic resistance element mounted close to the vibratile element and consisting of a block of porous material composed of sintered particles of a metal such as copper. In one embodiment, Fig. 7, two opposite corners 52, 53 of a twister type piezo-electric element 51 are cemented to a circular non-flat diaphragm 49, and the remaining two corners 54 are cemented to the back plate 45 of the unit. In front of the diaphragm 49 is mounted a porous sintered metal member 47, which is shaped to conform to that of the diaphragm 49, and the volume of the enclosure 50 and the size of the minute air-channels through the porous member 47 are so related to each other and to the vibratory system that resonancefrequency vibrations are effectively damped. In another construction, Figs. 1 to 3 (not shown), the piezo-electric element is mounted between two diaphragms, sintered metal elements, forming a case, being provided over each diaphragm. A further construction in which porous sintered elements are mounted between two piezo-electric elements is described with reference to Figs. 5 and 6 (not shown). Specifications 409,040 and 463,766 are referred to.