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Verifit User’s Guide Version 2.8
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12 Real-Ear Directional Test
12.1 Section overview
FastFacts 12.1: Real-ear directional test
Directional characteristics such as polar plots and Directivity Index (DI) are
typically measured in a large anechoic chamber using sound from one direction at
a time and often presented one frequency at a time. These methods assume a
hearing aid set for linear amplification and an environment free of reflections. In
most real situations sounds arrive simultaneously from all directions due to
reflections from walls, floors and ceilings, and the hearing aid is not linear.
The Verifit directional test presents over 1000 tones simultaneously at different
frequencies from both front and back REM speakers. The tones are individually
controlled in real time to produce a precise spectrum from each speaker at the
REM reference microphone. They are then separated in the measured real-ear
SPL and displayed as two real-time response curves, labeled F (front) and B
(back) to indicate which speaker generated the curve. Since the curves are
generated simultaneously, their difference is not influenced by electronic
processing such as compression but reflects only the effects, static or adaptive,
produced by the directional microphones in the instrument.
Because this measurement is carried out in a real room, results are not expected
to agree with data taken in large anechoic chambers. Results do represent
directional performance in the location in which the measurement is being made.
Due to strong reflected signals, measurements made in small reverberant rooms
will show small 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 large acoustically “dead” room, 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 the clogging of ports.
See
12.2: REM directional testing
