Characteristics
Main Purpose
ANSI specifies the NBS 9A Coupler for calibrating the earphones of audiometers. It has been
chosen because of it’s simple construction and because the threshold transfer data of so many
different earphones have already been determined.
Volume
It has a volume of about 5.6 cm
3
which approximates the volume enclosed by a supra-aural ear-
phone on a human ear.
Frequency
The output level of an earphone on a real ear measured below 500 Hz is lower because of leak-
age and flesh compliance. From 500 Hz to 1500 Hz, it is about the same for both ear and cou-
pler.
Between 1500 Hz and 8000 Hz, the response of the coupler is a fair indication of the earphone’s
performance. However this cannot necessarily be used as a precise indication of the relationship
between coupler and ear because of complex interactions between the earphone and its acoustic
load.
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LI0078 – 28 September 2017
