IEC 61669:2015

IEC 61669 ®
Edition 2.1 2025-01
CONSOLIDATED VERSION
INTERNATIONAL
STANDARD
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inside
Electroacoustics – Measurement of real-ear acoustical performance
characteristics of hearing aids

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IEC 61669 ®
Edition 2.1 2025-01
CONSOLIDATED VERSION
INTERNATIONAL
STANDARD
colour
inside
Electroacoustics – Measurement of real-ear acoustical performance
characteristics of hearing aids
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 17.140.50 ISBN 978-2-8327-0151-5
REDLINE VERSION – 2 – IEC 61669:2015+AMD1:2025 CSV
© IEC 2025
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 8
4 Test setup diagrams . 13
5 Limitations . 15
6 Test equipment . 16
6.1 Safety requirements . 16
6.2 Ambient conditions. 16
6.3 Test signal . 16
6.4 Sound field source . 17
6.5 Coupled sound source . 17
6.6 Test signal range . 17
6.7 Test signal level indication . 17
6.8 Equalization . 17
6.9 Frequency . 17
6.10 Harmonic distortion . 17
6.11 Probe microphone measurement . 17
6.12 Noise floor of probe microphone measurement . 17
6.13 Attenuation of probe microphone to external signals . 18
6.14 Analysis characteristics. 18
6.15 Output indication . 18
6.16 Graphical printout . 18
7 Test conditions . 19
7.1 Ambient conditions in the test space . 19
7.2 Background noise . 19
7.3 Acoustical properties . 19
7.4 Sound field characteristics . 19
7.5 Calibration . 19
7.6 Equalization . 19
7.6.1 General . 19
7.6.2 Substitution method . 19
7.6.3 Modified pressure method – Stored equalization . 20
7.6.4 Modified pressure method – Concurrent equalization . 20
7.7 Test signal level . 20
7.8 Location of the subject . 20
7.9 Location of the tester . 20
7.10 Location of the field reference point . 20
7.11 Location of the measurement point . 21
7.12 Instructions to the subject . 21
7.13 Location and coupling of the hearing aid . 21
7.14 Operating conditions for the hearing aid . 21
8 Measurements . 21
8.1 General . 21
8.2 Real-ear unaided response (REUR) curve. 21

© IEC 2025
8.3 Real-ear unaided gain (REUG) curve . 22
8.4 Real-ear occluded response (REOR) curve . 22
8.5 Real-ear occluded gain (REOG) curve . 22
8.6 Real-ear aided response (REAR) curve. 22
8.7 Real-ear aided gain (REAG) curve . 23
8.8 Real-ear insertion gain (REIG) curve . 23
8.9 Real-ear to coupler difference (RECD) curve . 23
8.10 Real-ear to dial difference (REDD) curve . 23
9 Measurement uncertainty for the performance requirements of Clause 6 . 24
Annex A (informative) Positioning the probe microphone sound inlet at the
measurement point . 25
A.1 General . 25
A.2 Visual positioning . 25
A.3 Acoustically-assisted positioning . 25
A.4 Acoustic positioning – Method 1 . 26
A.5 Acoustic positioning – Method 2 . 26
A.6 Geometrical positioning . 26
Annex B (informative) Issues in RECD measurement and application . 27
B.1 General . 27
B.2 Influence of the coupled sound source . 27
B.3 Estimating ear canal SPL produced by a hearing aid. 30
B.4 Correcting an HL audiogram obtained with an insert earphone and a
standard eartip . 32
B.5 Correcting an HL audiogram obtained with an insert earphone and a custom
earmould. 33
Annex C (informative) Relationship between tolerance interval, corresponding
acceptance interval and the maximum permitted uncertainty of measurement . 35
Bibliography . 36

Figure 1 – Test set-up . 14
Figure 2 – Real-ear measurement arrangement . 15
Figure B.1 – Computer-simulated ECLD for an average adult ear . 29
Figure B.2 – Computer-simulated ECLD for an average 3-month old child’s ear . 29
Figure B.3 – Computer-simulated error in estimating SPL in an average adult ear . 31
Figure B.4 – Computer-simulated error in estimating SPL in an average 3-month old
child’s ear . 32
Figure B.5 – Computer-simulated HL correction for an average 3 month old child’s ear . 34
Figure C.1 – Relationship between tolerance interval, corresponding acceptance
interval and the maximum permitted uncertainty of measurement . 35

Table 1 – Tolerance limits, acceptance limits and U for basic measurements . 24
max
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INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ELECTROACOUSTICS –
MEASUREMENT OF REAL-EAR ACOUSTICAL
PERFORMANCE CHARACTERISTICS OF HEARING AIDS

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
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agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
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5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
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6) All users should ensure that they have the latest edition of this publication.
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) IEC draws attention to the possibility that the implementation of this document may involve the use of (a)
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https://patents.iec.ch. IEC shall not be held responsible for identifying any or all such patent rights.
This consolidated version of the official IEC Standard and its amendment has been
prepared for user convenience.
IEC 61669 edition 2.1 contains the second edition (2015-11) [documents 29/886/FDIS
and 29/893/RVD] and its amendment 1 (2025-01) [documents 29/1179/CDV and
29/1194/RVC].
In this Redline version, a vertical line in the margin shows where the technical content
is modified by amendment 1. Additions are in green text, deletions are in strikethrough
red text. A separate Final version with all changes accepted is available in this
publication.
© IEC 2025
International Standard IEC 61669 has been prepared by IEC technical committee 29:
Electroacoustics.
This second edition cancels and replaces the first edition of IEC 61669:2001 and the first
edition of ISO 12124:2001. This edition constitutes a technical revision.
This edition includes the following significant technical changes with respect to
IEC 61669:2001 and ISO 12124:2001:
a) the addition of the International Speech Test Signal as a preferred speech-like stimulus;
b) definitions and test methods for the real-ear to dial difference;
c) definitions and test methods for the real-ear to coupler difference and
d) an annex dealing with issues in the measurement and application of the real-ear to
coupler difference;
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
The committee has decided that the contents of this document and its amendment will remain
unchanged until the stability date indicated on the IEC website under webstore.iec.ch in the
data related to the specific document. At this date, the document will be
• reconfirmed,
• withdrawn, or
• revised.
IMPORTANT – The "colour inside" logo on the cover page of this document indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
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© IEC 2025
INTRODUCTION
The performance characteristics of hearing aids in actual use can differ significantly from
those determined in accordance with standards such as IEC 60118-0, and IEC 60118-7, due
to differing acoustic influence and coupling presented by individual ears. Measuring methods
that take into account the acoustic coupling and the acoustic influence of the individual
wearer on the performance of hearing aids are therefore important in the fitting of these
devices. Such measuring methods have come to be known as “real-ear measurements” and
are sometimes performed clinically in less than ideal acoustic environments. The accuracy
and repeatability of measurements made under such conditions are complex functions of the
sound field, the test environment, the nature of the test signal, the hearing aid under
evaluation, the method of test signal control, the location of the sound field source, the nature
of the data acquisition, analysis and presentation as well as the degree of subject movement
permitted.
This standard provides definitions for terms used in the measurement of real-ear performance
characteristics of hearing aids, provides procedural and reporting guidelines, and identifies
essential characteristics to be reported by the manufacturer of equipment used for this
purpose. Acceptable tolerances for the control and measurement of sound pressure levels
are indicated. Where possible, sources of error have been identified and suggestions provided
for their management.
© IEC 2025
ELECTROACOUSTICS –
MEASUREMENT OF REAL-EAR ACOUSTICAL
PERFORMANCE CHARACTERISTICS OF HEARING AIDS

1 Scope
This International Standard gives recommendations and requirements for the measurement
and estimation of the real-ear acoustical performance characteristics of air-conduction
hearing aids and for the measurement of certain acoustic properties of the ear related to the
application of hearing aids.
Measurements of real-ear acoustical characteristics of hearing aids which apply non-linear or
analytical processing techniques are valid only for the test signals used and conditions
employed.
The purpose of this standard is to ensure that measurements of real-ear acoustical
performance characteristics of a given hearing aid on a given human ear can be replicated in
other locations with other test equipment.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60601-1, Medical electrical equipment – Part 1: General requirements for basic safety
and essential performance
IEC 60601-1-2, Medical electrical equipment – Part 1-2: General requirements for basic safety
and essential performance – Collateral Standard: Electromagnetic disturbances –
Requirements and tests
IEC 60318-5, Electroacoustics – Simulators of human head and ear – Part 5: 2 cm coupler
for the measurement of hearing aids and earphones coupled to the ear by means of ear
inserts
IEC 60942, Electroacoustics – Sound calibrators
IEC 61260-1, Electroacoustics – Octave-band and fractional-octave-band filters – Part 1:
Specifications
ISO 266, Acoustics – Preferred frequencies
ISO 8253-2, Acoustics – Audiometric test methods – Part 2: Sound field audiometry with pure-
tone and narrow-band test signals
ISO/TR 25417, Acoustics – Definitions of basic quantities and terms

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3 Terms and definitions
For the purpose of this document, the terms and definitions of ISO/TR 25417 and the
following apply:
3.1
test signal
acoustic signal at the field reference point
3.2
coupled sound source
earphone or hearing aid receiver and any tubing used to couple its acoustic output, without
leakage, to the ear canal or the cavity of a coupler
3.3
free sound field
sound field where the boundaries of the room exert a negligible effect on the sound waves
Note 1 to entry: In practice, a free sound field is a field in which the influence of reflections at the boundaries or
other disturbing objects is negligible over the frequency range of interest.
[SOURCE: ISO 8253-2:2009, 3.12, modified (addition of note to entry)]
3.4
quasi-free sound field
sound field where the boundaries of the room exert only a moderate effect on the sound
waves
[SOURCE: ISO 8253-2:2009, 3.13]
3.5
subject
person in whose ear the hearing aid performance is characterized
3.6
subject reference point
point bisecting the line joining the centres of the openings of the ear canals of the subject (at
the junction between concha and ear canal)
Note 1 to entry: In cases where severe head shape abnormality or asymmetry make it difficult to determine the
reference point of the subject, the subject reference point used should be stated.
3.7
subject test position
position with subject seated in a reproducible upright position with the head erect and the
subject reference point located on the test axis at the working distance
3.8
test axis
line through the centre of the surface from which sound exits the sound field source and in the
direction of maximum acoustic radiation
SEE: Figure 1.
3.9
test point
reproducible position on the test axis at which the subject reference point is located for test
purposes
© IEC 2025
SEE: Figure 1.
3.10
working distance
distance from the subject reference point to the plane of the mounting ring or protective grille
of the sound field source measured along the test axis
SEE: Figure 1.
3.11
SPL
sound pressure level
ten times the logarithm to the base 10 of the ratio of the square of the sound pressure, p, to
the square of a reference value, p
2 2
L = 10lg(p /p ) dB
p 0
where the reference value, p , is 20 µPa
Note 1 to entry: Sound pressure level is expressed in decibels.
Note 2 to entry: Because of practical limitations of the measuring instruments, p is always understood to denote
the square of a frequency-weighted, frequency-band-limited or time-weighted sound pressure.
Note 3 to entry: This note applies to the French version only.
[SOURCE: ISO/TR 25417:2007, 1.2]
3.12
BSPL
band sound pressure level
SPL for a specified frequency band
Note 1 to entry: This note applies to the French language only.
3.13
test signal level
SPL of the test signal at the field reference point
Note 1 to entry: For broad-band signals the bandwidth of the SPL measurement and the BSPL as a function of
frequency should be specified and stated.
3.14
equalization
process of controlling the test signal level as a function of frequency such that it does not vary
from the desired level
3.14.1
concurrent equalization
real time equalization
equalization performed at the time of measurement based on the monitoring of the test signal
level
3.14.2
stored equalization
equalization performed at the time of measurement based on data recorded during a prior
measurement of the sound field

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3.15
reference microphone
controlling microphone
microphone used to measure the test signal level in the measurement process and/or to
control it in the equalization process
SEE: Figure 2.
3.16
sound inlet
aperture through which sound enters a microphone and at which the microphone is calibrated
3.17
field reference point
point at which the sound inlet of the reference microphone is located during equalization
and/or measurement
SEE: Figure 2.
3.18
probe microphone
microphone adapted to explore a sound field without significantly disturbing it
Note 1 to entry: If the probe microphone utilizes a probe tube; this tube is considered part of the probe
microphone and its open end is the probe microphone sound inlet.
3.19
test ear
ear of the subject in which the probe microphone sound inlet is placed
3.20
measurement point
point in the ear canal of the test ear at which the probe microphone sound inlet is placed
3.21
axis of rotation
straight line about which the subject can be rotated, passing through the subject reference
point and lying in the vertical plane of symmetry
SEE: Figure 1.
3.22
azimuth angle of sound incidence
angle between the plane of symmetry of the subject and the plane defined by the axis of
rotation and the test axis
SEE: Figure 1.
Note 1 to entry: When the subject faces the sound field source, the azimuth angle of sound incidence is defined
as 0°. When the test ear of the subject faces the sound field source, the azimuth angle is defined as 90°. When the
non-test ear faces the sound field source, the angle is defined as –90°.
3.23
subject reference plane
horizontal plane that contains the subject reference point
SEE: Figure 1.
© IEC 2025
3.24
elevation angle of sound incidence
angle between the subject reference plane and the test axis
SEE: Figure 1.
Note 1 to entry: When the sound field source is directly above the subject, the elevation angle is defined as +90°.
When the test axis lies in the subject reference plane, the elevation angle is defined as 0°.
3.25
test signal type
identification of the test signal in terms of its frequency spectrum and/or temporal properties
3.26
maximum length sequence
MLS
periodic pseudo-random binary sequence of length one less than an integer power of two,
whose circular autocorrelation function is an impulse
Note 1 to entry: This note applies to the French language only.
3.27
substitution method
method of measurement using stored equalization with the reference microphone located at
the subject reference point and the subject absent during the recording of the SPL at the test
point
3.28
modified pressure method
method of measurement using stored or concurrent equalization with the field reference point
near the surface of the head of the subject close to the test ear, but outside the acoustic
influence of the pinna and the hearing aid
Note 1 to entry: The exact location of the field reference point should be specified by its perpendicular distance
from the surface of the head and its distance (in millimetres) forward of and above or below the centre of the ear
canal entrance.
3.29
differential comparison
measurement in which the test signal level is subtracted from the SPL at the measurement
point
Note 1 to entry: When using broad-band signals, BSPL should be used.
3.30
real-ear unaided response
REUR
SPL as a function of frequency at the measurement point in the unoccluded ear canal for a
specified test signal level
Note 1 to entry: When using broad-band signals, BSPL should be used.
Note 2 to entry: This note applies to the French language only.
3.31
real-ear unaided gain
REUG
difference, as a function of frequency, between the SPL at the measurement point in the
unoccluded ear canal and the test signal level
Note 1 to entry: When using broad-band signals, BSPL should be used.

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Note 2 to entry: This note applies to the French language only.
3.32
real-ear occluded response
REOR
SPL as a function of frequency at the measurement point for a specified test signal level, with
the hearing aid in place and switched off
Note 1 to entry: This note applies to the French language only.
3.33
real-ear occluded gain
REOG
difference as a function of frequency, between the SPL at the measurement point and the test
signal level, with the hearing aid in place and switched off
Note 1 to entry: When using broad-band signals, BSPL should be used.
Note 2 to entry: This note applies to the French language only.
3.34
real-ear aided response
REAR
SPL as a function of frequency at the measurement point for a specified test signal level, with
the hearing aid in place and switched on
Note 1 to entry: The term Real-Ear Saturation Response (RESR) has sometimes been used for the REAR with a
stimulus SPL of 85 dB or 90 dB. The use of this term is deprecated in favour of REAR85 or REAR90.
Note 2 to entry: This note applies to the French language only.
3.35
real-ear aided gain
REAG
difference as a function of frequency, between the SPL at the measurement point and the test
signal level, with the hearing aid in place and switched on
Note 1 to entry: When using broad-band signals, BSPL should be used.
Note 2 to entry: This note applies to the French language only.
3.36
real-ear insertion gain
REIG
difference as a function of frequency, between aided response and unaided response (REIG =
REAR – REUR), or between aided gain and unaided gain (REIG = REAG – REUG)
Note 1 to entry: It is assumed that REAR and REUR have been derived using the same test signal.
Note 2 to entry: REIG is expressed in decibels.
Note 3 to entry: This note applies to the French language only.
3.37
real-ear to coupler difference
RECD
difference as a function of frequency, between the SPL produced near the tympanic
membrane in an occluded ear canal by a coupled sound source having a high acoustic
impedance and that produced in the 2 cm coupler specified in IEC 60318-5 by the same
coupled sound source connected directly to its cavity
Note 1 to entry: This note applies to the French language only.

© IEC 2025
3.38
real-ear to dial difference
REDD
difference as a function of frequency, between the SPL produced near the tympanic
membrane by an audiometric sound source and the hearing level indicated by the audiometer
driving the sound source
Note 1 to entry: This note applies to the French language only.
3.39
curve
real-ear acoustical characteristic expressed and graphically displayed as a function of
frequency
EXAMPLE Real-ear aided response curve.
3.40
crest factor
ratio of the peak sound pressure to the root-mean-square sound pressure of the test signal
Note 1 to entry: When expressed in decibels, crest factor is the difference between the peak and r.m.s levels of
the test signal.
3.41
long term average speech spectrum
LTASS
SPL in contiguous one-third-octave bands measured over the duration of a speech sample
4 Test setup diagrams
The following two figures illustrate the relationship between the subject and the parts of the
measurement system that deliver and receive sound.

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IEC
Key
1 Plane of symmetry
2 Azimuth angle of sound incidence
3 Test axis
4 Subject reference point and Test point
5 Sound source
6 Working distance
7 Elevation angle of sound incidence
8 Subject reference plane
9 Axis of rotation
Figure 1 – Test set-up
© IEC 2025
IEC
Key
1 Hearing aid or earmould
2 Measurement point and probe microphone sound inlet
3 Marking or marking device
4 Probe tube (part of probe microphone)
5 Field reference point
6 Probe microphone (includes a probe tube if used)
7 Reference microphone
Figure 2 – Real-ear measurement arrangement
5 Limitations
Measurements of real-ear acoustical performance characteristics of hearing aids are
influenced by the following factors:
• type of hearing aid,
• test signal,
• method of equalization,
• test environment,
• signal analysis characteristics
• result analysis and presentation,
• degree of subject movement permitted,
• hearing aid – subject interface,
• physical characteristics of the subject.

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6 Test equipment
6.1 Safety requirements
Equipment shall conform to the requirements of IEC 60601-1 and IEC 60601-1-2.
6.2 Ambient conditions
Performance requirements shall be met for the following ambient conditions:
Temperature: 18 °C to 28 °C
Relative humidity: 20 % to 80 %
Atmospheric pressure: 81,3 kPa to 106,3 kPa
If other conditions apply, these conditions shall be stated. If the calibration of the
measurement system depends on ambient conditions, corrections for such dependence shall
be made.
6.3 Test signal
The equipment manufacturer shall report the test signal type(s) provided by the equipment
and shall supply the information listed below for each type. For hearing aids employing
advanced signal processing techniques the International Speech Test Signal (ISTS) specified
in IEC 60118-15 should be used.
For a pure-tone test signal, report the frequency spacing (if stepped) and total harmonic
distortion.
For a tone burst, report the frequency spacing (if stepped), the ON and OFF times for the
burst, the number of repetitions at each frequency and the SPL during the ON time of the tone
burst.
For a warble tone test signal, report the frequency spacing (if stepped), modulating frequency,
frequency deviation, and type of modulating waveform.
For a narrow-band noise test signal, report the frequency spacing (if stepped), effective
bandwidth, slope of band skirts, and the spacing of frequency components within the band (if
pseudo-random).
For a random noise test signal, report the crest factor and frequency spectrum employed.
For pseudo-random noise, chirp, and click test signals, report the spacing and number of
frequency components, lowest frequency present, frequency spectrum employed, repetition
rate, and crest factor.
For an MLS test signal, report order, sampling rate, crest factor, and frequency spectrum
employed.
For a speech-like test signal, report the test signal level and the bandwidth over which it is
determined, the LTASS and, if digitized, the sampling rate and number of bits. If the test
signal is standardized or commercially available, report the source and identifying information.
The International Speech Test Signal (ISTS) specified in IEC 60118-15 is the preferred
speech-like test signal.
If the speech has been modified by other than linear filtering, a description of the processing
or a reference where it can be found should be provided.

© IEC 2025
Measurements of real-ear acoustical performance characteristics of hearing aids which use
non-linear or analytical processing techniques are valid only for the test signals and
conditions employed. These measurements should be performed in accordance with the
hearing aid manufacturer’s recommendations, as they can require specific test signals or test
conditions outside the scope of this standard.
6.4 Sound field source
When using the substitution method, the sound field source shall consist only of coaxial
elements. In order to avoid reflections, the frontal surface of the sound field source enclosure
shall be covered with a suitable absorbing material. When using the modified pressure
method these restrictions do not apply.
6.5 Coupled sound source
The magnitude of the acoustic impedance of the coupled sound source used in the
measurement of the RECD shall be at least 3.16 times that of the occluded test ear and of the
2 cm coupler.
6.6 Test signal range
Narrow-band test signal levels shall cover the range from 50 dB to 90 dB at a working
distance of 0,5 m in an anechoic environment, with a maximum step size of 5 dB.
6.7 Test signal level indication
For the range of levels indicated by the equipment manufacturer, when measured at the inlet
to the reference microphone, the indicated test signal level as a function of frequency shall be
accurate within 4 dB.
6.8 Equalization
In an anechoic environment, equalization shall allow the test signal to be controlled, as a
function of frequency, to within 4 dB of the intended test signal level at the field reference
point at a working distance of 0,5 m.
6.9 Frequency
The frequency, or components, of the test signal shall cover the frequency range from 200 Hz
to 8 000 Hz (i.e. covering the one-third octave bands from 250 Hz to 6 300 Hz).
The indicated frequency of a narrow-band test signal or the indicated centre frequency of the
analysis bands for a broad-band test signal shall be accurate within 3 %.
6.10 Harmonic distortion
For a pure-tone test signal in an anechoic environment, the total harmonic distortion of the
test signal at the field reference point at a working distance of 0,5 m shall not exceed 3 %.
6.11 Probe microphone measurement
For the measurement range indicated by the equipment manufacturer, the probe
microphone measurement shall be accurate within 4 dB over the frequency range 200 Hz to
8 000 Hz (i.e. covering the one-third-octave bands from 250 Hz to 6 300 Hz).
6.12 Noise floor of probe microphone measurement
When the probe microphone sound inlet is acoustically sealed, the indicated SPL, as a
function of frequency, shall be at least 10 dB below the lowest level to be measured over the

REDLINE VERSION – 18 – IEC 61669:2015+AMD1:2025 CSV
© IEC 2025
frequency range 200 Hz to 8 000 Hz, for pure tones, or in the one-third-octave bands from
250 Hz to 6 300 Hz for broad-band signals.
Care shall be taken to avoid errors caused by extraneous noise when verifying this indication.
6.13 Attenuation of probe microphone to external signals
When the probe microphone sound inlet is acoustically sealed and placed in a sound field, the
SPL, as a function of frequency, measured by the probe microphone, shall be at least 10 dB
lower than the lowest level to be measured with the sound inlet open, over the frequency
range 200 Hz to 8 000 Hz, for pure tones, or in the one-third octave bands from 250 Hz to 6
300 Hz for broad-band signals.
The sound field used for this measurement shall be uniform over the surface of the entire
probe microphone and of sufficient level to cause the measured SPL to exceed the noise floor
of the probe microphone by at least 10 dB.
6.14 Analysis characteristics
The equipment manufacturer shall report the analysis type(s) employed by the equipment and
shall supply the information listed below for each type.
For analysis of a tone-burst test signal, report the integration time of the SPL measurement if
different from the ON time of the tone-burst.
For broad-band analysis, report the measurement bandwidth and integration time.
For spectrum analysis employing a swept filter, report the filter bandwidth and skirt slope.
For spectrum analysis employing digital means, report sampling rate, digital resolution,
averaging time or number of averages, analysis bandwidth, block length, windowing type,
window overlap, method (synchronous, FFT auto-spectrum, FFT cross-spectrum, digital filter),
and total frequency range of analysis. For analysis using a digital filter bank, report centre
frequencies, bandwidth and integration times. Octave or fractional-octave band filters should
conform to IEC 61260 Class 2.
Preferred frequencies are the one-third-octave frequencies specified in ISO 266.
6.15 Output indication
The output indicator used shall give r.m.s. value indication within 2 dB of the true r.m.s. value
for the type of signal to be measured.
If, under certain conditions, it is necessary to use a selective measuring system, e.g. filtering,
to ensure that the response of the hearing aid to the test signal can be differentiated from
inherent noise in the hearing aid, the use of the selective system should be stated in the
report.
NOTE The type of output indicator employed can influence the test results significantly if a non-sinusoidal voltage
is being measured. Such non-sinusoidal voltages can be present when making measurements with high input levels
to the hearing aid.
6.16 Graphical printout
It is recommended that frequency response curves be plotted on a grid having a linear decibel
ordinate scale and a logarithmic frequency abscissa scale with the length of one decade on
the abscissa scale equal to the length of (50 ± 2) dB on the ordinate scale.

© IEC 2025
7 Test conditions
7.1 Ambient conditions in the test space
The operator shall ensure that the equipment has reached a stable operating condition and
that ambient conditions in the test space at the time of test are within the ranges specified in
6.2. If other conditions apply, these conditions shall be stated. If the calibration of the
measurement syste
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