46 FONIX FP35 Hearing Aid Analyzer
for a 3 dB error at 500 Hz, the reference quality will be “3.” Only the worst
error is indicated. In order to minimize the effect of noise and other problems
on the reference quality, only the frequencies between 260 Hz and 6000 Hz are
checked for quality.
Most of the chamber quality errors encountered will be the result of probe tube
errors. Doing a custom calibration of the probe microphone with the probe tube
that will be used with the measurement will improve this. It will not make the
response “perfect,” because minor changes in the probe tube placement can
result in minor variances in the readings. It is normal to have one to two dB
errors with the probe tube, even when it’s in the sound chamber. Sound field
errors may even be greater because of noise and reflections.
Note: When RMS ANALYSIS is set to NONE, the reference RMS and quality sig-
nal will not be measured. See Section 2.5.3 on the RMS analysis method.
2.5.5 Using the Earphone Jack
The earphone jack on the FP35 analyzer is normally used for RECD measure-
ments and telecoil measurements. However, it might also be used for special
purpose testing, such as a loop-back cable to test electrical (non-acoustic) opera-
tion, or a special user-supplied transducer, such as one that might be used to
test a cochlear implant. It is not used as an external speaker jack, which has its
own connector.
By default, the earphone jack on the back of the FP35 is disabled in all screens
except the Audiogram Entry screen when the telecoil is disabled. (See Section
2.5.8 for details on telecoil measurements.) This is to prevent confusion and to
make sure that if an external speaker is being used, it is plugged into the proper
speaker jack instead of the earphone jack.
You can choose to deliver the FP35 analyzer’s signal to:
• Onlythespeaker(thiscanbeinternalorexternal)
• Onlytheleftchanneloftheearphonejack
• Boththeleftandrightchannelsoftheearphonejack
• Bothchannelsoftheearphonejackandthespeakersimultaneously
To select the output device:
1. Set the USER LEVEL to ADVANCED in the Default Settings menu. See Section
2.3.3.
2. Press [MENU] in the measurement screen.
3. Press [NEXT] twice to enter the Custom menu.
4. Select OUTPUT JACK using the [∧ ∨] keys.
