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10 On-Ear Instrument Measures
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 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 directional test overview
The Verifit directional test measures directional performance in real-time and displays simultaneous curves
representing stimulus delivered to the front and back of the hearing instrument. It is compatible with all forms of
hearing aid processing, including frequency lowering, feedback compensation, and other non-linear algorithms.
Speech is added as a conditioning signal to ensure automatic, speech-activated directional programs become
active.
Test levels are selectable in 5 dB steps. When speech is active it is presented from the front speaker and noise is
presented from the back speaker(s) at a selectable signal-to-noise ratio. At periodic intervals, the level of the
speech and noise is momentarily reduced and an additional noise burst is played from either the front or back
speaker to measure the response from that direction. This burst is extremely fast and will not influence the
behavior of the hearing aid. The measured SPL is analyzed into two curves labeled F (front) and B (back) to
indicate which speaker generated the curve. The real-time nature of the test allows the operation of adaptive
directional systems to be readily visualized.
Optionally, speech may be disabled which will cause the directional test to alternate noise bursts from the front
and back speaker. This test may not produce a directional response in all hearing aids.
Once directional performance is observed, the test may be terminated.
Because this measurement is carried out in a real room, results are not expected to agree with data taken in large
anechoic chambers. Due to strong reflected signals, measurements made in small, reverberant rooms will show
less separation between front and back response curves, just as the benefits of directional technology will
become less apparent in similar situations. When performed in a sound booth or relatively anechoic space, this
test can be used to demonstrate and verify directional benefit and to provide assurance that the directional
microphone array has been correctly assembled and programmed and has not deteriorated due to element drift or
clogged ports.
On-ear directional testing
Best results are obtained using external front and back sound field speakers positioned well away from reflective
surfaces. See External sound field speaker setup. 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 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. Right-click the mouse to raise the Home prompt and select [Directional] under On-ear.
3. Select which ear to test, or select the binaural link to test both ears (Dual view only).
4. Select Test 1, 2, 3 or 4 by pressing
test – the thick curve is the response from the front speaker and the thin curve the response to the back
speaker signal. For a non-directional instrument, the two curves will be nearly identical. Setting the
instrument for directional operation should produce a separation of the curves.
5. On the Test control poster, select a level from the [Level] drop-down list. For an adaptive directional
Verifit
®
User's Guide Version 4.8 © November 2016
. Two real-time curves will appear on the screen for each ear under
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