Condenser and Carbon Microphones-Their Construction and Use*

Abstract

Of the numerous microphones which have been developed since Bell's original work on the telephone, only two are used extensively in sound recording for motion pictures, namely, the condenser microphone and the carbon microphone. The condenser microphone was first proposed in 1881 but owing to its low sensitivity was limited in its field of usefulness until the development of suitable amplifiers. In 1917, E. C. Wente published an account of the work which he had done on a condenser microphone having a stretched diaphragm and a back plate so designed as to introduce an appreciable amount of air damping. The major portion of the condenser microphones used today in sound recording embody the essential features of the Wente microphone. Marked progress has, however, been made in the design and construction of these instruments with the result that they are not only more sensitive but also more stable. The factors which contribute to this improvement are described in detail in this paper. Recently a number of articles have appeared in the technical press calling attention to certain discrepancies between the conditions under which the thermophone calibration of the condenser microphone is made and those which exist in the studio. The nature of these discrepancies and their bearing on the use of the microphone are discussed. Microphones in which the sound pressure on the diaphragm produces changes in the electrical resistance of a mass of carbon granules interposed between two electrode surfaces have been used commercially since the early days of the telephone. In recent years the faithfulness of the reproduction obtained with the carbon microphone has been materially improved by the introduction of an air damped, stretched diaphragm and a push‐pull arrangement of two carbon elements. This instrument is finding extensive use in sound recording and reproduction fields where carbon noise is not an important factor. The outstanding design features of the push‐pull carbon microphone are described in this paper and suggestions made as to the precautions to be taken in its use if the best quality, maximum life, etc. are to be obtained.

A Novel Multi-Bit Sigma-Delta Modulator using an Integrating SAR Noise-Shaped Quantizer

“…Microphones can be implemented using several technologies, such as carbon microphones [3], [4], condenser microphones [4], [5] dynamic microphones, electret microphones [6], fiber-optic microphones [7], [8], piezoelectric microphones and MEMS microphones. Carbon microphones were very popular in the early days of electronics due to its low cost and robustness.…”

Long-Term Stability of One-Inch Condenser Microphones Calibrated at the National Institute of Standards and Technology

“…The next 20 years saw the development of the thermophone, a calculable source of sound for calibrating microphones [ 12 ], substantial expansion of the theory underlying microphone calibrations [ 13 – 17 ], and the development of improved condenser microphone designs suitable for mass production [ 18 , 19 ]. The commonly used calibration methods required independent knowledge of the magnitude of the applied sound pressure, based either on independent (non-microphonic) measurements [ 10 ], or on the use of a calculable source [ 12 ].…”