Frye FONIX FP40D User Manual

Page 54

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46

FONIX FP40 Portable Hearing Aid Analyzer

3. Use the FREQUENCY and AMPLITUDE knobs to select DISTORTION under PURE-TONE

SETTINGS.

4. Press START/STOP to toggle between displaying the harmonic distortion in “bar” format on

the graph or “table” format next to the graph.

5. Use the AMPLITUDE to select DIST TYPE.

6. Press START/STOP to select the type of harmonic distortion measurement to make. See

Section 2.4.1.4 for more details.

7. Press F1 to return to the Main Coupler Screen.

8. Run a pure-tone frequency response by following the directions found in Section 3.4.2. The

harmonic distortion results will appear either as bars on the graph or as a separate table.

3.4.7 Viewing battery current drain

Follow the directions in Section 2.6 for instructions on turning on the battery drain display and
selecting the appropriate battery pill. You must use a composite or pure-tone sweep source.

You must use a battery pill to view battery current drain.

3.4.8 Switching between gain and output

Look at the screen just above F2 and F3. If one of the function button labels reads “ON GAIN” or
“OFF GAIN,” press the corresponding function button (F2 or F3) to toggle the selection. This will
switch between viewing the response graph in dB GAIN or dB SPL.

When you view the graph in dB GAIN, you are looking at the difference between the input (the
source signal) and the output (measured by the analyzer’s microphone). This is nice because you
are seeing only what the hearing aid is amplifying.

When you view the graph in dB SPL, you are viewing everything that is measured by the analyzer’s
microphone. The source signal is not subtracted.

3.4.9 Testing with the reference microphone

You can use the FP40 to perform coupler measurements with or without the reference microphone.
We generally recommend to test without the reference microphone when performing coupler mea-
surements because it’s easier, faster, and almost as accurate. However, testing with the reference
microphone, when done correctly, is slightly more accurate than testing without it. See Figure 3.4.9
for pictures of aids tested with the reference microphone.

Things to keep in mind when testing with the reference microphone:

• You must relevel the sound chamber with the reference microphone every time you switch

hearing aids. See Section 3.2.2 for instructions.

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