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Electroacoustics studies conversion between electrical signals and sound, together with the measurement and control of that conversion. A microphone produces an electrical response to an acoustic input; a loudspeaker performs the reverse conversion. Their frequency responses, loading and directional behavior matter as much as a single sensitivity number.

For a receiving microphone, one can define the complex frequency response $M_p(f)=V(f)/p(f)$ in volts per pascal, with the electrical termination and acoustic conditions specified. Equal outputs do not imply equal incident sound pressures if the two microphones have different sensitivities. Calibration supplies the link between the electrical recording and an acoustic measurement.

A motivating primary method is microphone reciprocity calibration. In the NIST system reported by Randall P. Wagner and collaborators, three laboratory microphones are measured in pairs using acoustic coupling cavities. One microphone transmits while another receives; known coupling properties and reciprocity relations allow the individual pressure sensitivities to be determined without starting from a separately calibrated reference microphone. Comparing results with different cavity lengths tests the acoustic corrections and associated measurement uncertainty.^[ref]

W. Marshall Leach, Jr. was an electrical engineer whose work included audio electronics, electroacoustics, electronic instrumentation and low-noise circuit design. His research and teaching connected audio power amplifiers with loudspeaker systems and acoustic measurement.^[ref]

His notes The Junction Diode by W. Marshall Leach, Jr. develop the relationship between the physical junction and the circuit models used to analyze it. That connection is useful in audio engineering as well: a model must capture the relevant device behaviour while remaining simple enough to reason about bias, signal variation and distortion.^[ref]

Identity and biography: leachlegacy.ece.gatech.edu/bio.html