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13 On-Ear Instrument Measures
Section overview
A number of the tests covered in Test box measures can also be performed with the hearing
instrument coupled to the ear of a client rather than to a 2cc coupler. The on-ear results
may be expected to differ from the test box results because of the different acoustic
environment and the different acoustic load.
On-ear feedback test
This test shows the SPL and the power concentration ratio (PCR) in each 1/3 octave band
for a speech signal. Feedback results in a peak in the speech spectrum and in the PCR.
Incipient feedback results in a peak in the PCR curve.
Refer to On-Ear Measures - Setup to prepare the system for use and for proper positioning
of the client and the probe tube.
1. Insert the earmold/tip or custom hearing instrument into the ear, being careful not to
advance the probe tube further into the ear canal. A lubricant applied in the vicinity of
the probe tube will ease insertion and prevent slit leaks.
2. Set the instrument as it will be used, with feedback suppression enabled and initialized.
3. Press <Tests> then highlight and <PICK> [On-ear measures], then highlight and
<PICK> [Feedback].
4. Highlight and <PICK> Test 1 and set the Stimulus to Speech-std(1) or (2) and the level to
50 or 60 dB SPL. As the speech passage plays, observe the feedback bar and the lower
graph. A yellow Feedback bar and peaks with yellow markers in the lower curve indicate
incipient feedback which may impact sound quality. A red Feedback bar and peaks with
red markers in the lower curve indicate feedback that may be audible and should be
mitigated. Press <Continue> to run the full speech passage and capture average results
for the passage.
5. Repeat for Test 2 and 3 as needed. These tests may be used to explore the effects of jaw
movement and the presence of hands, hats and telephone handsets.
On-ear noise reduction test
This test captures a response curve before the hearing instrument reacts to the presence of
noise; a comparison curve shows the hearing instrument reacting in real-time. The thick
curve is the output before the noise reduction is activated and the thin line is the output as
the noise reduction takes effect. The test also provides an overall rms noise reduction value
in dB.
Refer to On-Ear Measures - Setup to prepare the system for use and for proper positioning
of the client and the probe tube.
1. Press <Tests>, then highlight and <PICK> [On-ear measures], then highlight and pick
[Noise reduction].
2. Highlight and <PICK> Test 1, 2 or 3.
3. Highlight and <PICK> a stimulus type from the list box.
4. Highlight and <PICK> a stimulus level from the list box.
User's Guide Version 3.4 © June 2011
RM500SL
®
60
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