The self-fitting hearing aid
Elizabeth Convery, Harvey Dillon, Gitte Keidser, Lyndal Carter, and Dan Zhou
National Acoustic Laboratories, Sydney, Australia
Supporting Research
Of the 278 million people in the
world with bilateral moderate to
profound hearing loss, twothirds live in developing
countries (WHO, 2004). Most
could benefit from amplification,
but fewer than 3% of people in
developing countries who need
a hearing aid actually have one.
More than 30 million hearing aids – and staff to fit them – are
needed annually in developing countries, but current annual
provision is less than 1 million. Annual production of hearing aids is
estimated to meet less than 10% of global need. Barriers to
effective hearing rehabilitation services in developing countries
include the cost of hearing aids relative to income, the availability
and cost of batteries and repairs, the lack of a professional
infrastructure, and the stigma associated with hearing loss and the
use of amplification (Brouillette, 2008).
Two issues that are fundamental to the design of a self-fitting
hearing aid are the reliability and validity of (1) automatic
audiometry, and (2) audiometric threshold measurement using
stimuli generated by the hearing aid. The results of a recent study
conducted at NAL demonstrates that an automatic measurement of
thresholds, conducted by the client without the assistance of an
audiologist, yields results that are as valid as those obtained with
manual audiometry (Carter et al., unpublished data). Test-retest
reliability was also found to be high.
What is a self-fitting hearing aid?
A second NAL study confirmed
that in situ measurement of air
conduction thresholds can be
made using stimuli that are
generated by the hearing aid
itself, as long as transducerspecific correct factors are
applied and ambient noise does
not exceed the level of the test
stimuli (O’Brien et al., submitted).
Real ear to
coupler
difference
Adjust hearing
aid
70
70
60
60
50
50
40
40
30
30
20
20
10
10
0
0
data shown for 1 kHz
0
10
20
30
40
50
60
data shown for 1 kHz
-10
-10
70
Manual thresholds (dB HL)
Mean REDD (dB)
-10
-10
Automatic retest threshold (dB HL)
A self-fitting hearing aid is an amplification device that users can
program themselves, without direct input from an audiologist. The
proposed device incorporates an in situ adaptive measurement of
the user’s hearing thresholds, to which an onboard prescriptive
algorithm is applied to determine an appropriate gain/frequency
response and compression characteristics.
Automatic thresholds (dB HL)
Introduction
0
10
20
30
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60
70
Automatic test threshold (dB HL)
20
15
10
5
0
-5
-10
Insert
Closed
Open
-15
-20
100
1,000
10,000
Frequency (Hz)
Response
button
NAL-NL2
prescription
formula
Test
controller
Signal
generator
Hearing thresholds
Prescription
algorithm
Automatic
Audiometer
DAC and
amplifier
determining who is a
candidate for a selffitting hearing aid
measuring and
accounting for
conductive loss
Desired amplification
characteristics
Hearing aid
adjuster
Hearing aid signal
processor
Advantages
Disadvantages
 low cost
 direct professional input not
required
 real-world environments used
in fitting process
 greater psychological
ownership of fitting process and
outcome
 risk of audiologically
inappropriate fitting
 risk of aid-induced hearing
loss
 high level of cognitive function
required
creating sound value
Future
Research
measuring client
benefit and
satisfaction
comparing outcomes
to traditional fitting
procedures
References
Brouillette R. (2008) Rehabilitation of hearing loss: challenges and opportunities in developing countries. In B.
McPherson, R. Brouillette. Audiology in Developing Countries. New York: Nova Science Publishers, Inc.
Carter L, Dillon H, Zhou D. Unpublished automatic audiometry data.
Goulios H, Patuzzi R. (2008) Education and practice of audiology internationally: affordable and sustainable education
models for developing countries. In B. McPherson, R. Brouillette. Audiology in Developing Countries. New York: Nova
Science Publishers, Inc.
O’Brien A, Keidser G, Yeend I, Hartley L, Dillon H. (submitted) Validity and reliability of in situ air conduction
thresholds measured through hearing aids coupled to closed and open instant-fit tips.
WHO (2004) Guidelines for hearing aids and services for developing countries. Geneva: World Health Organization.
www.hearingcrc.org