Microphone for athletic fields, to its two sides of sound waves from remote sound sources have free access

摘要

146,105. Miessner Inventions Corporation, (Assignees of Miessner, B. F.). June 23, 1919, [Convention date]. Microphones; mouthpieces.-Relates to transmitters of the kind described in Specification 140,070 in which sound is admitted to both sides of the diaphragm to nullify the effect of sounds from sources in the plane of the diaphragm. According to the present invention, the back of the diaphragm is secured from the direct impact of sounds coming from behind, and in order that the vibrations of the diaphragm may be moderate when a person in a noisy place shouts into the instrument, the diaphragm is made thick so as to have a high natural frequency. In the form shown in Fig. 1, sounds reach the front and rear of the diaphragm d2 equally through holes 26, 25 respectively. Direct access from sound sources behind the diaphragm is prevented by the casing 20, and felt or other packing 27 may be used to prevent internal reflexion and resonance. In the form shown in Fig. 2, a diaphragm d' of double the ordinary thickness and a natural frequency of 2000 is held in a thin ring 49 in a recess, in the front plate 44, which is mounted on the back plate 40 by means of screws 46 and spacing washers 45.