112 FONIX FP40 Portable Hearing Aid Analyzer
The difference curve, labeled “Insertion Gain” on the screen, shows the benefit of adding the second
microphone for sound arriving from the “bad” side.
5.9.2.3 Overall Insertion Gain
Note: Since it has not been shown for CROS and BI-CROS instruments that a 45º position of the
loudspeaker improves the reliability of insertion gain measurements, we recommend a 45º position
of the loudspeaker only for monaural instruments, and a 0º position for CROS and BI-CROS instru
-
ments.
CROS
A. Unaided—Measurement of “good” ear
Set up the FP40 analyzer as follows.
• Reference microphone ON
• Sound field LEVELED
• Reference microphone over pinna of bad ear
• Probe microphone inside unoccluded ear canal of
good ear
• Loudspeaker at 0º, 12 inches from bridge of nose
B. Aided—Measurement of “good” ear
Same setup as A, except:
• Aid in place in good ear and set to user gain.
The difference curve, labeled “Insertion Gain” on the screen, shows the overall benefit of inserting
the hearing aid.
BI-CROS
A. Unaided—Measurement of “better” ear
Set up the FP40 analyzer as follows:
• Reference microphone ON
• Sound field LEVELED
• Unaided response CUSTOM
• Reference microphone over pinna of bad ear
• Probe microphone inside unoccluded ear canal of bet
-
ter ear
• Loudspeaker at 0º, 12 inches from bridge of nose
REFERENCE MIC
PROBE MIC
12"
SPEAKER
GOOD
EAR
BAD
EAR
BETTER
EAR
REFERENCE MIC
PROBE MI
C
12"
BAD
EAR
SPEAKER
