BRUEL & KJAER 4185, User Manual

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Adjusting the Ear Simulator Force
12 Ear Simulator for Telephonometry Type 4185
User Manual
3.2 Adjusting the Ear Simulator Force
Using Type 4185 requires sealed conditions, therefore, it is essential for
the measured response that there is no leakage between the handset
earcap and the ear coupler. This can be checked in four ways:
1) With the receiver energized (low frequency), adjust the ear
simulator force until audible sound is at a minimum.
2) With the measurement equipment set up and using a low test
frequency (for example 200 Hz), adjust the ear simulator force until
maximum output from the microphone in the ear simulator is
detected.
3) With the measurement equipment set up, measure the frequency
response repeatedly and adjust the ear simulator force for
maximum low-frequency response (see Fig. 3.2).
4) Use the built-in seal check facility of Type 4185. The procedure is
very similar to using a low test frequency as explained above, but
the built-in sound source of Type 4185 has the advantage of
delivering a constant volume velocity so that the resulting SPL in
the ear simulator is independent of the receiver sensitivity.
ITU-T recommends an application force between 8 and 10 N for
placing earcaps against the ear simulator. An application force higher
than 10 N will affect the performance of the coupler.