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Design of a Studio-Quality Condenser Microphone Using Electret Technology

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The performance requirements of a studio-quality condenser microphone are reviewed in light of present recording, broadcast, and sound reinforcement practice. Consideration is given to both electroacoustical performance and environmental stability. A condenser transducer is described which makes use of refined electret technology and demonstrates performance advantages over similar conventional, externally biased configurations. The details of a new RLC -lossy ladder- acoustical phase shift network are presented in basic terms as applied to the design of a cardioid unidirectional microphone. Finally a unique impedance conversion electronics section is described in terms of noise level, load driving capability, distortion, and environmental stability.

JAES Volume 26 Issue 12 pp. 947-957; December 1978
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Scott Dorsey
Scott Dorsey

Comment posted January 30, 2018 @ 21:45:40 UTC (Comment permalink)

Two previous versions of this paper had been given at conventions, but this one, published in the JAES, is the final and most complete one.  This is the paper that introduces the SM-81 and which contains a schematic of the early SM-81 (although people using this information for maintenance should beware that over the many decades in which the SM-81 has been manufactured the electronics have been completely revamped several times).

This paper is interesting for the insight into the design process of the SM-81 and into the various constraints on microphone performance which have not changed even today.  It is a useful source of service information for people who might be repairing the SM-81.  It is a useful source of design information for people who might be designing a new microphone.  When it came out, it was revolutionary; aside from a few Sony products of limited reliability, this was the first high performance electret microphone available to studios and sound reinforcement people, and it was the first condenser microphone of any sort that would work outside in the rain.  This paper explains why.

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