Calibration of earphones remains a weak link in many operational and research procedures. Often the small laboratory or field installation has difficulty justifying an expensive coupler system for earphone calibration, and even with such systems the process is surprisingly time-consuming.
The problem reported here was twofold—to seek a simple method of calibration which would employ only the more commonly found laboratory equipment and, second, to examine the feasibility of application of such a method to the self-, or internal, calibration of equipment such as the audiometer.
The procedure employed makes use of the fact that an earphone operates both as an earphone and as a microphone, although with markedly differing response characteristics. When an earphone is used as a microphone it is common for the response characteristic to show a decrease in sensitivity below 1000 cps of about 10 db. per octave, and resonance points will shift slightly upward