Frye FONIX FP40D - Manual (Page 59)

Coupler Measurements 51
5. Use the AMPLITUDE knob to select an appropriate source level. Typically this measurement
should be done so that it is above the noise floor of the testing environment, but below the
compression knee point of the aid, if possible. If you have a quiet testing environment, use
50 dB SPL. Noisier testing environments may require you to use a higher source level to get a
good measurement.
6. Press START/STOP to start the measurement. Press it again to stop the measurement once it
has stabilized.
Figure 3.6.2—Testing the forward coupler response of a directional aid
3.6.3. Taking the Reverse Measurement
1. Position the hearing aid so that it is faced away from the sound field speaker. Different hear-
ing aids have different null points, so you will want to adjust the positioning so that the
sound field speaker is pointing towards what should be the null point of the directional aid.
See Figure 3.6.3.
2. Make sure the aid is the same distance from the speaker that you used for the forward mea-
surement.
3. Press F6 to select CURVE 2.
4. Make sure the source type and level are selected that you used for the forward measurement.
5. Press START/STOP to start the measurement. If you are using a Digital Speech or Composite
source, you can actually rotate the hearing aid while the measurement is running to deter-
mine the null spot of the directional microphones – look for when the response drops the
most.