Audioscan Axiom - Manual (Page 68)

Axiom ® User's Guide Version 1.8  May 2015
For similar reasons, the on-ear RECD measurement is performed with a foam eartip, rather than the earmold.
This minimizes the error that arises from unknown lengths of tubing added to the RECD transducer. These
tubing effects can now be accounted for during the simulation on the coupler.
The ANSI RECD protocol can pose certain challenges in clinical implementation so alternate methods of RECD
measurement are possible. Test-box Speechmap allows the selection of coupling for BTE instruments (HA-1 or
HA-2) so the more traditional HA-2 (BTE) coupler can be utilized.
RECD protocols
A measured RECD is used both for simulation in the coupler (Test-box Speechmap) and for correcting HL
thresholds measured with insert phones.
For threshold corrections in the HL-to-SPL transform, the Axiom uses an HA-1 RECD or an HA-2 RECD
including tubing effects, based on whether the stated HL transducer is Insert+foam or Insert+mold respectively.
If the RECD was measured with an earmold, these tubing effects will be specific to the client’s earmold; if it is
measured with a foam tip, they will be based on average earmold tubing.
For Test box Speechmap involving BTE instruments the earmold tubing must be considered. If the BTE is
coupled to the HA-1 coupler using the personal earmold, the tubing effects will be part of the measurement. If
the HA-2 (BTE) coupler is used, the HA-1 referenced RECD will be converted to an HA-2 RECD. As with the
threshold correction above, the use of the earmold in RECD will include the effects specific to the client’s
earmold, otherwise an average earmold is assumed.
The following describes acceptable RECD measurement protocols and Test-box Speechmap coupling
combinations for BTE instruments and the implications of each in the test box simulation.
ANSI S3.46 method:
RECD On-ear measurement: Audioscan RECD transducer + foam eartip
Test-box Speechmap coupling: client’s personal earmold + HA-1 (ITE) coupler
With this method, RECD is a property of the ear only, and not dependent on the transducer or sound source
coupling. The earmold effects will be part of the measurement in the test box. Measured RECD is
appropriate for coupler simulation and error is minimized.
Alternate method #1:
RECD On-ear measurement: Audioscan RECD transducer + client’s personal earmold
Test-box Speechmap coupling: HA-2 (BTE) coupler
This method utilizes the client’s personal earmold for the on-ear RECD measurement. The HA-1 RECD is
converted to HA-2 reference with earmold effects retained and is applied in Testbox Speechmap. The error
introduced is the difference between the earmold effects when connected to the hearing instrument receiver
and earmold effects when connected to the RECD transducer.
If the total earmold tubing length is less than 35mm, it is recommended that Foam tip be selected in the
RECD Coupling field. This will bypass the correction and increase accuracy for small earmolds.
Alternate method #2:
RECD On-ear measurement: Audioscan RECD transducer + foam eartip
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