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The Japan Audio Society (JAS) has a special designation “Hi-Res Audio” which their member companies may use if they can demonstrate output to 40 kHz. Even using the small volume couplers such as the 0.4cc coupler, it is difficult to measure earphones at ultrasonic frequencies due to coupler resonances. Instead, Knowles has developed a technique using a free air measurement by placing a reference microphone 6 mm away from the eartip outlet and at a 90 degree angle. This minimizes resonant effects in the measurement while demonstrating the ultrasonic output to 40 kHz is indeed present. The measurement is taken in an anechoic chamber to prevent outside noise from interfering.
PTM Published on: 2015-02-20
