Real-Ear Measurements 111
5.9.2.2 How Well the Aid Overcomes the Head-Baffle Effect
CROS
A. Unaided—Measurement of “good” ear canal (baffled by head)
Set up the FP40 analyzer as follows.
• Reference microphone ON
• Sound field LEVELED
• Unaided CUSTOM
• Reference microphone over pinna of bad ear
• Probe microphone inside unoccluded ear canal
of good ear
• Loudspeaker at 90º, 12 inches from bad ear
B. Aided—Measurement of “good” ear canal (baffle
overcome by aid)
Same setup as A, except:
• Aid in place in good ear and set to normal user gain.
The difference curve, labeled “Insertion Gain” on the screen, shows the benefit the aid gives for
sound arriving from the “bad” side.
BI-CROS
A. Unaided—Measurement of “better” ear canal (baffled by head)
Set up the FP40 analyzer as follows.
• Reference microphone ON
• Sound field LEVELED
• Unaided set to CUSTOM
• Reference microphone over pinna of “bad” ear
• Probe microphone inside ear canal of better ear
• Hearing aid in better ear,
on, set at use gain
• Transmitter on bad side turned
off
• Loudspeaker at 90º, 12 inches from bad ear
B. Aided—Measurement of “better” ear canal (baffle overcome by aid)
Same setup as A, except
• Transmitter on bad side turned on
REFERENCE MIC
PROBE MIC
12"
BETTER
EAR
BAD
EAR
SPEAKER
REFERENCE MIC
PROBE MIC
12"
GOOD
EAR
BAD
EAR
SPEAKER
