106 FONIX FP40 Portable Hearing Aid Analyzer
5.7.6 Accounting for venting effects
You can make 2-cc targets more accurate by modifying the target to account for venting effects.
Frequency (Hz) 250 500 750 1k 1.5k
Tight Seal — — — — —
Slit Leak 2 2 1 — —
1 mm 1* 2* 1 — —
2mm 7* 1* — — —
Long Open 17* 10* 4* 1* —
Short Open 26* 21* 14* 10* 5*
Target Coupler FOG Vent Corrections
Note: Use starred values only if prescribed insertion gain is greater than 0 dB at that frequency.
Otherwise, use no correction. Blanks indicate use no correction. A slit leak is assumed for all vent
conditions except “Tight Seal.”
5.7.7 Understanding the technical details
For those of you who are interested in how we came about the correction factors used in the Target
2-cc screen, here is the technical information.
Average unaided
The “average” ear data is from KEMAR, large, right ear, measured with the reference microphone
one centimeter above the apex of the pinna, with the probe tube microphone opening approximate
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ly 17 mm into the ear canal, with the loudspeaker at ear level, 12 inches from the head surface at
an azimuth angle of 45 degrees.
Average RECD
The occluded ear SPL was measured using an Etymotic Research ER-3A insert earphone, with the
foam tip inserted 12 mm into the same KEMAR ear as above, with the probe microphone 5 mm
beyond the sound opening. The 2-cc coupler SPL was measured with the ER-3A attached to the
opening of an HA-1 coupler, using the same probe-microphone arrangement as in the occluded ear.
Aid-type
Same KEMAR ear and configurations of the reference microphone and loudspeaker as for the aver
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age unaided ear correction. No correction for BTE, because the reference microphone is precisely at
the location of the hearing aid microphone. ITE and Canal corrections are each the average of three
measurements with three probe-microphone locations at the surface of simulated hearing aid face
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plates.
