A condenser earphone with multiple layers of thin solid dielectric material between a metal backplate and a metallized foil is described. The multilayer system has the advantage of providing a more uniform air‐cushion between the electrodes, thus increasing efficiency and decreasing distortion.
The frequency response of this earphone has been measured on a standard 6‐cm3 coupler. The response is flat within ±1.5 dB between 25 and 14 000 cps and within ±3 dB between 20 and 16 500 cps. In this frequency range the harmonic distortion is less than 1% and the intermodulation distortion is less than 3% at 100 dB SPL. Because of the phase linearity, the pulse response of the earphone is an almost true image of the applied voltage for pulses not containing frequencies above 15 000 cps.
The frequency response of the earphone has also been measured at seven human ears by the outer‐ear canal method. The individual frequency response is flat within ±7 dB from 70 to 14 000 cps. For any one frequency, the sound‐pressure deviation between individual ears is within ±6 dB.
The high quality of this earphone makes it useful for many purposes where preservation of signal wave‐form is important, particularly in psycho‐acoustic experiments.