188 FONIX FP35 Hearing Aid Analyzer
8. While the “eee” is still sounding and once the curve on the screen has sta-
bilized, press [START/STOP] again. Note the total RMS Output in the ear
canal as indicated in the status box.
9. If the SPL seems high, you might modify the vent size. Then select AIDED 2
with [F2] and, if necessary, use [∨] to turn off the source. Repeat steps 7 and
8. You should see a change in the RMS Output. Aided Curve 2 should be
less than Aided Curve 1.
10. If desired, press [PRINT/FEED] to print the results.
Note: You could also measure the effects with the hearing aid on.
A
pp licAtio n 2: i nsertion g A i n meAs ure men ts u s i n g A n e xt ern Al s o u n d s o u r c e .
For this procedure the choice of sound source is yours. You may want to use
a tape or a CD player through a loudspeaker. Any sustained sound source will
work. Whether you use a cocktail noise tape or one of the new, environment
CDs, you should find your test results interesting, especially when testing non-
linear signal processing hearing aids.
Suggested Procedure:
1. Prepare your sound source
2. Enter the IG Screen of the Real-ear Mode.
3. Do a typical UNAIDED and AIDED probe test using your external sound
source by taking measurements with the internal source of the FP35 off.
8.3 Technical Details
The FONIX analyzers use phase synchronous signal sources to generate sound.
This means that the sound has a predetermined repeatable source, which allows
FONIX analyzers to make accurate measurements and use time averaging to
improve the signal to noise measurement of the analyzer.
When you take spectrum measurements with the FP35, a sound source is not
generated, and it is assumed that you will be measuring a non-repeating source
such as speech or room noise. In most cases, these measurement results are
improved with the use of a spectrum mode windowing filter. The windowing
filter helps to make the signal seem like it is synchronous to the analysis rou-
tines.
Unfortunately, using the windowing filter on a synchronous source signal will
result in mangling the results. You can see this by placing the FP35’s measure-
ment microphone in another analyzer’s chamber along side that analyzer’s own
microphone. The results will not look the same on the two analyzers. The way
to resolve this is to turn off the spectrum windowing filter. You can only do this
in Coupler Multicurve and Target Coupler screens.
