Frye FONIX 7000 - Manual (Page 193)

Appendix D
185
The FONIX CIC Feature
Background
Zwislocki built an ear simulator coupler years ago to better approximate the real
ear’s impedance variation with frequency. The ear’s volume appears to get larger
at lower frequencies. Mahlon Burkhard at Industrial Research Products agreed
with this approach, especially when they built the KEMAR, and designed an ear
simulator that had impedance changes that matched the Zwislocki figures. This
ear simulator was later standardized by the publication of American National
Standards Association standard, S3.25. Another ear simulator that has similar
characteristics was introduced in Europe a few years later by Bruel and Kjaer,
and is characterized in the standard IEC 711.
Frye Electronics introduced a slightly different approach in the 1980’s when
it came out with the INSITU option (and later, the OES option) for its 5500-Z
hearing aid Analyzer. Realizing that ear simulators which contain frequency
sensitive elements are somewhat fragile and can be damaged as they are
handled in every day use, Frye made a coupler which it labeled the MZ (for
Modified Zwislocki). This coupler had a central volume very similar to the
standardized Zwislocki, but had no frequency sensitive elements. Instead, an
analyzer program was used with the coupler to apply correction factors to the
measured curves from the hearing aid so that the output was very similar to that
which would be obtained if the aid were tested on a standardized ear simulator
as built by Knowles or B&K.
These software corrections work well for most regions in the frequency response
of the aid. In low frequency areas up to about 1500 Hz, if the aid has a response
peak that is influenced by the volume of the cavity, the peak will be slightly
higher in amplitude and slightly higher in frequency than that peak would be if
the aid were measured in a standardized ear simulator. The CIC hearing aid is
not usually affected by this problem.
The Need for a CIC Coupler
The introduction of the CIC hearing aids has made it desirable to be able to
test them with a coupler that more closely approximates the actual volume
and frequency response characteristics of the real ear. The CIC aid fits so close
to the tympanic membrane (TM) of the ear that the volume of the cavity is
reduced greatly and the aid produces a significant amount more gain. Further,
its response can be expected to be substantially influenced by the frequency
dependent impedance variations of the TM.
Frye Electronics felt that the use of a CIC coupler with a proper response cor-
rection would give better data to a hearing professional than the use of the stan-
dard 2 cc coupler or even a Zwislocki ear simulator when attempting to produce