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0611 RM500SL User’s Guide Version 2.8 Page 89
20.3 HIT high distortion or noise
FastFacts 20.3: HIT high distortion or noise
20.4 HIT curves inconsistent
FastFacts 20.4: HIT curves inconsistent
High distortion and/or noise numbers in an ANSI test
v There may be a leak between the hearing instrument under test and the
coupler it is connected to. For BTE type instruments, check the integrity of the
#13 tubing at the end of the coupler where it joins with the ear hook. Look for
cracks. ITE type instruments need to have a good seal between the hearing
instrument and the coupler. In addition, all vents need to be closed from the
faceplate side of the hearing instrument.
v Ambient room noise may be leaking into the test chamber. Air conditioners,
computer fans and similar noisemakers can yield artificially high noise figures.
Check the sealing of the test chamber. Try turning off suspected noise sources
to identify the cause.
v Vibration may be coupled into the test chamber from other equipment on the
same table or wooden floor. Computers, fans and air conditioners may be the
source of the vibration. Try turning off suspected sources to identify the cause.
Relocate the source or the RM500SL or mount it on a foam pad.
The HIT curves keep changing from test to test.
v The battery may be close to end of life or starved for air (zinc-air cells)
because of a tight seal on the battery compartment. Try a fresh battery or
using the optional RM500SL battery pill.
v The HIT reference microphone (the white one in the test chamber) is
incorrectly positioned. In order to control sound pressure levels precisely at the
microphone inlet of the hearing instrument, the HIT reference microphone
must be positioned as close as possible to the hearing instrument’s
microphone without actually touching it.
v The noise or feedback reduction features are attempting to reject the test
signal. These need to be disabled prior to tests with tones or noise.
v The instrument is on the verge of feedback due to a poor seal to the coupler,
unplugged vent or a crack in the tubing on the BTE coupler.