Abstract
Many speakers find it difficult to use the conventional type of microphone, because of the restrictions that it imposes upon their freedom of movement. A microphone, known as the lapel microphone, designed to be attached to the speaker's clothing, has been developed for overcoming these limitations. — The vibratory structure of the lapel microphone is designed to have low mass and stiffness, and to resonate at a comparatively high frequency. The resilient support of the diaphragm adds sufficient mechanical resistance to prevent the occurrence of a prominent peak in the response at the resonance frequency. Means are provided for reducing extraneous noise to a minimum. A part of the sound reaching the. microphone, due to body vibration, is rich in low frequencies and must be attenuated, otherwise the quality of transmission will be unnatural. This attenuation is accomplished in the coupling transformer, which, together with the apparatus required for suppressing clicks, for indicating when the circuit is in operation, etc., is mounted in a control cabinet. A flexible cord connects the microphone to this cabinet. — It is expected that the lapel microphone will find application in theaters, churches, convention halls, lecture and banquet rooms, and the like, where public address systems are now employed. It also can be applied in connection with other sound recording and reproducing equipment where the background noise, characteristic of carbon microphones, is not a limiting factor.
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