80 FONIX FP35 Hearing Aid Analyzer
Figure 3.8.2D—Comparison of the directional response of the hearing aid at 0 °(CRV1) and
180 °(CRV2)
3.8.3 Testing with the Reference Microphone
If your FP35 has the M300 microphone, you have two microphones available
for taking measurements. The normal, recommended method for taking coupler
measurements involves the use of just the coupler microphone. The second
microphone, referred to in Coupler Multicurve Mode as the “reference” micro-
phone, is normally set to OFF in the menu settings. (In Real-Ear Mode, this
microphone is referred to as the “probe” microphone.)
However, the FP35 is a true dual microphone system. This means that, if
desired, you can take your coupler measurements using both the coupler micro-
phone and the reference microphone. In this method, the analyzer compares the
response of the aid from inside the coupler with the coupler microphone to the
response of the sound chamber next to the microphone’s receiver with the refer-
ence microphone.
This method of using both microphones is technically more exact than the
normal method of using a single microphone. However, we have found that for
most practical purposes, there is little difference between using one or both
microphones. In fact, if you forget that the reference microphone is on, you
might accidentally leave it outside of the test box during measurements, lead-
ing to wild results. For this reason, we recommend leaving the reference micro-
phone off, unless you are doing research or have some other clinical reason for
measuring with it.
