Audioscan RM500 hearing aid AppNote

99-07
®
AppNote
• • • • • • • • • • • • • • • • •
Hearing aid performance in a
real ear differs from performance measured in a hearing
aid test box because the sound
reaching the hearing aid microphone is different (microphone
location effects), and because
the real-ear presents a different
acoustic load to the hearing aid
(acoustic impedance) than
does the 2cc coupler.
The RECD is defined as the
difference, in dB as a function
of frequency, between the SPL
produced by an insert transducer at the eardrum and in
a 2cc coupler.
Adult ear canal volumes are
typically in the range of .65 to
1.75 cc. Children’s ear canal
volumes are smaller. Generally,
the hearing instrument will
produce higher output in the
ear of the listener than in the
2cc coupler, because of the
smaller real-ear volume. This
is an important consideration
when fitting amplification,
especially for children.
The RECD measurement can be
performed at the time of the
hearing assessment. The values
can be printed and re-entered
when the client is seen on subsequent visits. The Audioscan
NOAH module can be used to
facilitate this process.
Etymonic Design Incorporated
41 Byron Avenue
Dorchester, Ontario
Canada N0L 1G0
1-800-265-2093 (USA)
Phone (519) 268-3313
Fax (519) 268-3256
Performing Real-Ear-to-Coupler Difference (RECD)
Measurements Using the Audioscan® RM500
with software version 2.6 or higher1
Because ears are different from 2cc couplers, a procedure has been implemented on
the Audioscan RM500 that quickly measures the individual’s unique ear-to-coupler
transform values. The real-ear-to-coupler difference (RECD) values for each individual
are derived by comparing the real-ear levels, measured by a probe microphone for a
given test signal, to the levels measured in a 2cc coupler for the same test signal across
frequencies.
SEVERAL CONSIDERATIONS SHOULD BE NOTED PRIOR TO MEASURING THE RECD:
•
•
•
•
•
An Audioscan RE770 RECD transducer or insert earphone coupled to a 1/4" to
RCA adapter is required to perform the RECD measurement.
On instruments not having an auxiliary loudspeaker jack, it will be necessary to
unplug the loudspeaker and plug the RECD transducer into the speaker jack.
REMEMBER to plug the speaker back in after the RECD measurement has been
completed.
The RECD is always measured using the BTE (HA-2) type coupler. The RM500 will
make any necessary mathematical corrections to ITE (HA-1) values. The RM500 will
also correct RECD measurements for deep insertion when CIC is selected as the
hearing aid type in DSL.
The coupler portion of the RECD measurement can be conducted prior to the
client’s arrival and need only be done once per power up.
If the transducer used for audiometric assessment purposes is an insert earphone
coupled to the client’s custom earmold, then the RECD should be measured using
the same earmold.
ACCESSING THE RECD MEASUREMENT PROCEDURE
To measure the RECD on the Audioscan RM500 real-ear system:
1. Calibrate both the hearing aid test (HAT) box and real-ear measurement (REM)
sections of the RM500 (see RM500 User’s Guide for details).
2. Ensure the RM500 is in REM mode. (If necessary, to select REM mode, press any
key in the REM area of the keyboard.)
3. Press the <ADVANCED FEATURES> key.
4. Highlight TESTS and SPEECHMAP/DSL. Press <CONTINUE>.
5. Press the <AGRAM> key to display the ASSESSMENT DATA ENTRY POSTER.
6. Using the cursor arrows on the keyboard, scroll through the window at each item
to select specific client information (AGE, TRANSDUCER, UCL, RECD and REDD).
Set the RECD window to MEASURE. Press <CONTINUE>.
7. Enter the client’s threshold information by following the onscreen instructions.
Press <CONTINUE>.
8. The RM500 will automatically advance to the RECD measurement procedure.
Onscreen instructions are provided to facilitate the measurement.
• • • • • • • • • • • • • • • • • •
Audioscan is a registered trademark of Etymonic Design Inc.
1
Software 2.6 is not available for RM500s with serial numbers lower than 1100.
The RECD measurement
procedure enables:
•precise definition of the individual’s auditory area for the
purposes of selecting and
fitting amplification;
•specification of hearing
instrument gain and SSPL90
(OSPL) in 2cc coupler terms
for hearing instrument
selection purposes;
•the capability to perform all
hearing instrument response
shaping in the controlled
conditions of the hearing
instrument test box;
•the ability to measure the
acoustic properties of a
child’s ear and earmold
coupling; and
•a substantial reduction in the
amount of time and degree of
cooperation required in the
fitting process.
COUPLER MEASURE
Complete details of how the
RECD measurement is used in
the Audioscan RM500
Speechmap/DSL fitting system
are provided in Cole & Sinclair
(1998).
5.
The measured RECD values, as
a function of frequency, should
generally be greater than or
equal to 0 dB. A negative RECD
value might indicate an inadequate seal of the foam coupling
(or earmold) in the ear, larger
than average ear, perforated
eardrum or myringotomy tube
in place.
Four curves will be displayed on the RM500
screen. The two curves on the upper portion of
the screen are the result of the current real-ear
measurement and the stored coupler measurement. The two curves on the lower portion of
the screen are the current measured RECD values and the age-appropriate average RECD values (for comparison purposes). If the
measured RECD curve is below -10 or unstable
in the low frequencies, check the seal of the
foam ear tip. If the measured RECD is below 0 in the 4 – 6 kHz region, check for
proper placement of the probe tube (i.e., within 5 mm of eardrum) and blockage of the
probe tube by the foam tip.
7. Press <CONTINUE> a second time to store the real ear curve (and RECD measurement).
1.
2.
3.
4.
5.
Plug the RE770 transducer into the auxiliary
speaker jack (located at the right rear of the HAT
box lid.)
Screw the BTE coupler onto the coupler microphone and plug into the microphone jack inside
the HAT box.
Couple the RE770 transducer to the BTE coupler
tubing. Lie coupler on RM500 keyboard or place
inside HAT box.
Press <CONTINUE> to introduce signal.
Press <CONTINUE> again to store the coupler
response.
REAL-EAR MEASURE
1.
2.
3.
4.
6.
Leave the RE770 transducer plugged into the
auxiliary speaker jack.
Unplug the coupler microphone and plug the
probe module into the microphone jack inside
the HAT box.
Prepare client for real-ear measurements. Ensure
probe tube is within 5 mm of eardrum (see
RM500 User’s Guide for details).
Couple the RE770 transducer to the standard
foam ear tip (or earmold tubing)
Insert the foam ear tip (or custom earmold) into
the ear. Wait for the coupling to seal at the ear
before proceeding.
Press <CONTINUE> to introduce signal.
REAL-EAR-TO-COUPLER DIFFERENCE (RECD) SCREEN
THE UNAIDED SPLOGRAM SCREEN
Reference:
Cole WA, Sinclair ST (1998).
The Audioscan RM500
Speechmap/DSL Fitting System.
Trends in Amplification,
3(4): 125-139.
• • • • • • • • • • • • • • • • •
Following completion of the RECD measurement procedure, the RM500 automatically
proceeds to the Speechmap/DSL unaided SPLogram screen. The measured RECD values
can now be obtained in numerical form at the top of the SPLogram printout by pressing
<PRINT SCREEN>. If desired, these RECD values can be re-entered into the RM500 at a
later date by scrolling to ENTER in the RECD window of the ASSESSMENT DATA ENTRY
POSTER.
Audioscan and Speechmap are trademarks of Etymonic Design Incorporated. DSL is a registered trademark of the University of Western Ontario.