Frye FONIX 7000 - Manual (Page 90)

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FONIX 7000 Hearing Aid Analyzer
Figure 3.4.11B—Forward directional measurement.
Reverse measurement
Next, open the sound chamber and position the hearing aid so that the front
of the hearing aid is pointing towards the left side of the chamber. See Figure
3.4.11C. Different hearing aids have different null points so you will want to
adjust the positioning so that the sound chamber speaker is pointing towards
what should be the null point of the directional aid. Close the sound chamber
lid when finished and perform the following steps:
1. Use [F2] to select the next curve.
2. Use [F5] to set the source type to Digital Speech.
3. Use [∨, ∧] to set the source amplitude to 50 dB SPL.
4. Press [START]. When the measurement has stabilized, press [STOP]. The
measured curve is the “reverse” measurement of the directional test. If the
directional microphones of the hearing aid are working properly, this curve
should have less output or gain than the forward measurement.
The difference in the RMS Out of the two curves will give you the average over-
all advantage provided by the directional microphones. See Figure 3.4.11D. In
this example, the hearing aid has an 8 dB average directional advantage.