IEC 61672-3:2013

IEC 61672-3 ®
Edition 2.0 2013-09
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Electroacoustics – Sound level meters –
Part 3: Periodic tests
Electroacoustique – Sonomètres –
Partie 3: Essais périodiques
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IEC 61672-3 ®
Edition 2.0 2013-09
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Electroacoustics – Sound level meters –

Part 3: Periodic tests
Electroacoustique – Sonomètres –

Partie 3: Essais périodiques
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX R
ICS 17.140.50 ISBN 978-2-8322-1078-9

– 2 – 61672-3  IEC:2013
CONTENTS
FOREWORD . 3
1 Scope . 5
2 Normative references . 5
3 Submission for testing . 6
4 Conformance . 6
5 Preliminary inspection . 7
6 Power supply . 7
7 Environmental conditions . 8
8 General test requirements . 8
9 Sound calibrator . 8
9.1 General . 8
9.2 Information for operation . 9
9.3 Information for testing . 9
9.4 Calibration of the sound calibrator . 9
10 Indication at the calibration check frequency . 9
11 Self-generated noise . 9
11.1 Microphone installed . 9
11.2 Microphone replaced by the electrical input-signal device . 10
12 Acoustical signal tests of a frequency weighting . 10
13 Electrical signal tests of frequency weightings . 12
14 Frequency and time weightings at 1 kHz . 13
15 Long-term stability . 14
16 Level linearity on the reference level range. 14
17 Level linearity including the level range control . 14
18 Toneburst response . 15
19 C-weighted peak sound level . 16
20 Overload indication . 16
21 High-level stability . 17
22 Documentation . 17

61672-3  IEC:2013 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ELECTROACOUSTICS –
SOUND LEVEL METERS –
Part 3: Periodic tests
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
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
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
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
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4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
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expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
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) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 61672-3 has been prepared by IEC technical committee 29:
Electroacoustics, in cooperation with the International Organization of Legal Metrology (OIML).
This second edition cancels and replaces the first edition published in 2006. This second
edition constitutes a technical revision.
The main technical changes with regard to the previous edition are as follows:
In this second edition, conformance to specifications is demonstrated when:
a) measured deviations from design goals do not exceed the applicable acceptance limits,
and
b) the uncertainty of measurement does not exceed the corresponding maximum-permitted
uncertainty, with both uncertainties determined for a coverage probability of 95 %.

– 4 – 61672-3  IEC:2013
The text of this second edition is based on that of the first edition and the following documents:
FDIS Report on voting
29/814/FDIS 29/825/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts in the IEC 61672 series, published under the general title Electroacoustics –
Sound level meters, can be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until the
stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data related to
the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A list of all parts of the IEC 61672 series, published under the general title Electroacoustics –
Sound level meters, can be found on the IEC website.

61672-3  IEC:2013 – 5 –
ELECTROACOUSTICS –
SOUND LEVEL METERS –
Part 3: Periodic tests
1 Scope
This second edition of IEC 61672-3 describes procedures for periodic testing of time-weighting,
integrating-averaging, and integrating sound level meters that were designed to conform to the
class 1 or class 2 specifications of the second edition of IEC 61672-1. The aim of the standard
is to ensure that periodic testing is performed in a consistent manner by all laboratories.
NOTE 1 In this document, references to IEC 61672-1, IEC 61672-2, and IEC 61672-3 refer to the second editions
unless stated otherwise.
NOTE 2 Procedures for the periodic testing of sound level meters designed to conform to the specifications of
IEC 61672-1:2002 were given in IEC 61672-3:2006.
The purpose of periodic testing is to assure the user that the performance of a sound level
meter conforms to the applicable specifications of IEC 61672-1 for a limited set of key tests
and for the environmental conditions under which the tests were performed.
The extent of the tests in this part of IEC 61672 is deliberately restricted to the minimum
considered necessary for periodic tests.
Periodic tests described in this edition of IEC 61672-3 apply to sound level meters for which
the manufacturer claims conformance to the specifications of the second edition of
IEC 61672-1. Periodic tests described in this part of IEC 61672 apply to sound level meters for
which the model has been, or has not been, pattern approved by an independent testing
organization responsible for pattern approvals in accordance with the test procedures of the
second edition of IEC 61672-2.
Because of the limited extent of the periodic tests, if evidence of pattern approval is not
publicly available, no general conclusion about conformance to the specifications of
IEC 61672-1 can be made, even if the results of the periodic tests conform to all applicable
requirements of this edition of IEC 61672-3.
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 60942, Electroacoustics – Sound calibrators
IEC 61094-5, Measurement microphones – Part 5: Methods for pressure calibration of working
standard microphones by comparison
IEC 61094-6, Measurement microphones – Part 6: Electrostatic actuators for determination of
frequency response
IEC 61183, Electroacoustics – Random-incidence and diffuse-field calibration of sound level
meters
– 6 – 61672-3  IEC:2013
IEC 61672-1, Electroacoustics – Sound level meters – Part 1: Specifications
IEC 61672-2, Electroacoustics – Sound level meters – Part 2: Pattern evaluation tests
IEC 62585, Electroacoustics – Methods to determine corrections to obtain the free-field
response of a sound level meter
ISO/IEC Guide 98-3, Uncertainty of measurement – Part 3: Guide to the expression of
uncertainty in measurement (GUM:1995)
ISO/IEC Guide 99, International vocabulary of metrology – Basic and general concepts and
associated terms (VIM)
3 Submission for testing
3.1 An instruction manual applicable to the model and version of the sound level meter shall
be available in order to perform periodic tests of a sound level meter. If an applicable
Instruction Manual is not submitted along with the sound level meter, nor available at the
laboratory, nor publicly accessible from the Internet web site of the manufacturer or supplier of
the sound level meter, then no periodic tests shall be performed.
3.2 The source for the instruction manual shall be described in the documentation for the
periodic tests.
3.3 All items or accessories for the sound level meter that are necessary for periodic testing
shall accompany the sound level meter when it is submitted for testing. A device specified in
the instruction manual for inserting electrical signals equivalent to signals from the microphone
shall also be submitted if requested by the laboratory.
3.4 Periodic tests as described in this part of IEC 61672 shall not be performed unless the
markings on the sound level meter are as required by IEC 61672-1 or there is evidence that the
sound level meter was originally so marked. The serial number and the model designation shall
be visible on the sound level meter.
3.5 Data required to perform the periodic tests shall be available and the source of the data
shall be recorded and reported by the laboratory. The data shall include all relevant information
required by IEC 61672-1 and IEC 62585.
3.6 A sound calibrator shall be available. The sound calibrator shall be supplied with the
sound level meter, if required by the user or if requested by the laboratory, or shall be supplied
by the laboratory. If a suitable sound calibrator is supplied by the user, it shall be used by the
laboratory to establish the acoustical sensitivity of the sound level meter.
4 Conformance
4.1 Conformance to a performance specification is demonstrated when the following criteria
are both satisfied: (a) a measured deviation from a design goal does not exceed the applicable
acceptance limit and (b) the corresponding uncertainty of measurement does not exceed the
corresponding maximum-permitted uncertainty of measurement given in IEC 61672-1 for the
same coverage probability of 95 %. IEC 61672-1 gives example assessments of conformance
using these criteria.
4.2 For laboratories performing periodic tests, the uncertainties associated with all
measurements shall be determined in accordance with the procedures of ISO/IEC Guide 98-3.
Metrological terms shall be as defined in ISO/IEC Guide 99. Actual measurement uncertainties
shall be calculated for a coverage probability of 95 %. Calculation of the uncertainty of

61672-3  IEC:2013 – 7 –
measurement for a particular test should consider at least the following components, as
applicable. Other uncertainty components are noted in Clauses 7, 12, and 13.
– The uncertainty attributed to calibration of the individual instruments and equipment used to
perform the test, including the sound calibrator and any free-field facility;
– The uncertainty resulting from environmental effects or adjustments;
– The uncertainty resulting from small errors that may be present in the applied signals;
– The uncertainty attributed to effects associated with the repeatability of the results of the
measurements. When a laboratory is only required to make a single measurement, it is
necessary for the laboratory to make an estimate of the contribution of random effects to
the total uncertainty. The estimate should be determined from an evaluation of several
measurement results previously obtained for a similar sound level meter;
– The uncertainty associated with the resolution of the display device of the sound level meter
under test. For digital display devices that indicate signal levels with a resolution of 0,1 dB,
the uncertainty component should be taken as a rectangular distribution with semi-range of
0,05 dB;
– The uncertainty associated with the device used to mount the sound level meter in the free-
field test facility;
– The uncertainty resulting from the deviation of the sound field in the free-field test facility
from an ideal free sound field; and
– The uncertainty associated with each correction applied to the measurement data.
4.3 If an actual uncertainty of measurement for a test performed by the laboratory exceeds
the corresponding maximum-permitted uncertainty, the result of the test shall not be used to
evaluate conformance to this part of IEC 61672 for periodic testing.
4.4 A laboratory’s actual uncertainty, without inclusion of the uncertainty of the
manufacturer’s free-field or random-incidence correction data, shall not exceed the
corresponding maximum-permitted uncertainty from IEC 61672-1. However, when the
uncertainty of the manufacturer’s correction data is included it is possible that an actual
uncertainty of measurement may exceed the corresponding maximum-permitted uncertainty
only because the uncertainty of the manufacturer’s correction data was a significant part of the
laboratory’s uncertainty budget. In this event, testing may proceed, but the documentation for
the periodic tests shall include a statement to explain the reasons that the results of a test did
not conform to a specification of IEC 61672-1.
5 Preliminary inspection
Prior to any measurements, the sound level meter and all accessories shall be visually
inspected, paying particular attention to damage to, or accumulation of foreign material on, the
protection grid or diaphragm of the microphone. All relevant controls shall be operated to
ensure that they are in working order. If the controls, display, and other essential elements are
not in proper working order, no periodic tests shall be performed.
6 Power supply
For all tests, the sound level meter shall be powered from its preferred supply or a suitable
alternative. Before and after conducting the set of tests with acoustical signals and before and
after conducting the set of tests with electrical signals, the power supply for the sound level
meter shall be checked by the method stated in the Instruction Manual to ensure that it is within
the specified operating limits. If the voltage or the equivalent indication of the status of the
power supply is not within the operating limits and the reason cannot be attributed to partially
discharged batteries or an incorrect selection of the voltage of the public power supply, then no
periodic tests shall be performed as a malfunction is indicated.

– 8 – 61672-3  IEC:2013
NOTE Changes to the output of the power supply can be determined as changes to the percentage of the voltage
from fully-charged batteries, or by an equivalent procedure.
7 Environmental conditions
7.1 Periodic tests shall be performed within the following ranges of environmental
conditions: 80 kPa to 105 kPa for static air pressure, 20 °C to 26 °C for air temperature, and
25 % to 70 % for relative humidity.
7.2 As a minimum, the static air pressure, air temperature, and relative humidity shall be
measured and recorded at the start and end of periodic testing.
7.3 Unless data are available for the influence on the model of a sound level meter of the
deviations in the prevailing environmental conditions from the reference environmental
conditions, for periodic tests of frequency weightings conducted at a static pressure less than
97 kPa, the laboratory shall assign a standard uncertainty of 0,09 dB for measurements at
frequencies less than or equal to 3 kHz and a standard uncertainty of 0,14 dB for
measurements at frequencies greater than 3 kHz.
NOTE The two standard uncertainties are for use when values for the standard uncertainties are not available
from the potential sources listed in 12.6. The two values were determined from estimates of 0,15 dB and 0,25 dB
respectively for the maximum influence of static pressure on frequency response for models of microphones that
have the greatest air stiffness in the back cavity.
8 General test requirements
8.1 Periodic tests described in subsequent clauses apply only for those design features that
are required by IEC 61672-1 and that are available in the sound level meter submitted for test.
All such features shall be tested.
8.2 For all periodic tests, the configuration of the sound level meter shall be as requested by
the user and shall be as specified in the Instruction Manual for one of the normal modes of
operation, including all required accessories. For a sound level meter that provides selectable
settings for corrections to the relative frequency response for the influence of any accessories
or for other configurations of the sound level meter, the tests shall be performed using the
settings that are appropriate for the configuration of the sound level meter in its normal mode
of operation. Any such settings shall remain unchanged throughout the testing.
8.3 Electrical signals shall be inserted into the sound level meter through the input device or
by the means specified in the Instruction Manual. The deviation of the frequency of an input
signal from a specified frequency shall not exceed ±0,25 % of the specified frequency.
8.4 For a sound level meter that has an electrical output that is to be used for periodic tests,
the indications obtained from the electrical output and the corresponding indications on the
display device of the sound level meter shall be confirmed to be identical within the acceptance
limits given in IEC 61672-1. Where multiple outputs are present, if an output is specified in the
Instruction Manual for testing, that output shall be used for periodic testing.
8.5 The laboratory shall use instruments that have been calibrated for the appropriate
quantities at appropriate intervals. As required, the calibrations shall be traceable to national
standards.
9 Sound calibrator
9.1 General
The sound calibrator shall preferably be a model specified in the Instruction Manual for use
with the sound level meter, or alternatively a sound calibrator producing the same nominal

61672-3  IEC:2013 – 9 –
sound pressure level and frequency as a model specified in the Instruction Manual. In the latter
case, any adjustments to be applied when that model of calibrator is coupled to the model of
microphone supplied on the sound level meter shall use publicly available data from either the
manufacturer of the sound level meter or the manufacturer of the sound calibrator.
NOTE It is possible that publicly available data for a model of sound calibrator that is not specified in the
Instruction Manual has not been verified according to IEC 61672-2.
9.2 Information for operation
Any adaptor required to couple the microphone of the sound level meter to the sound calibrator
shall be available. An Instruction Manual for the sound calibrator also shall be available. If an
appropriate sound calibrator, any necessary adaptor, or the Instruction Manual are not
available, no periodic tests shall be performed.
9.3 Information for testing
For periodic testing of a sound level meter, the sound calibrator shall be shown to conform to
the periodic-testing requirements for the applicable performance class of IEC 60942.
Conformance shall be demonstrated for sound pressure level, frequency, and total distortion
using the methods given in the applicable edition of IEC 60942. Evidence that the sound
calibrator conforms to the applicable requirements of IEC 60942 may be provided by
documentation from a periodic test performed in accordance with the procedures given in
IEC 60942. The laboratory may offer to perform a calibration for the sound calibrator.
9.4 Calibration of the sound calibrator
Calibration of the sound calibrator shall be performed using equipment for which calibration of
the appropriate quantities is traceable to national standards. The calibration of the sound
calibrator shall use the model of microphone supplied with the sound level meter, or an
equivalent model of microphone, or a suitable microphone along with correction data
appropriate to the model of microphone supplied with the sound level meter. When correction
data are used, the source of the data shall be the manufacturer of the sound calibrator,
microphone, or sound level meter, and shall be stated in the documentation for the periodic
tests. A calibration certificate for the sound calibrator showing the results of the calibration
shall be supplied.
10 Indication at the calibration check frequency
10.1 The indication of the sound level meter at the calibration check frequency shall be
checked by application of the sound calibrator described in Clause 9. The sound level meter
shall be adjusted, if necessary, to indicate the required sound level for the environmental
conditions under which the tests are performed. For multi-channel sound level meter systems,
the indication shall be checked for as many of the channels as are required to be tested. The
indications of the sound level meter before and after adjustment shall be recorded. If the
adjustment value was determined using a particular model of adaptor with the sound calibrator,
an adaptor of the same model shall be used when checking the indication of the sound level
meter.
10.2 The effect of the prevailing environmental conditions on the sound pressure level
produced in the coupler of the sound calibrator, relative to the sound pressure level produced
under the reference environmental conditions of IEC 61672-1, shall be accounted for in
accordance with the procedure and data from the Instruction Manual for the sound calibrator.
11 Self-generated noise
11.1 Microphone installed
– 10 – 61672-3  IEC:2013
11.1.1 Measurements of the level of self-generated noise shall be made in a location that is
available to the testing laboratory and where the level of background noise is minimized. Any
supplied windscreen and windscreen accessory need not be installed around the microphone
for measurement of the level of self-generated noise. The sound level meter shall be in the
configuration submitted for periodic testing and with the most-sensitive level range and
frequency-weighting A selected.
11.1.2 The indicated level of the A-weighted self-generated noise on the most-sensitive level
range shall be recorded and reported. The level of self-generated noise is preferably measured
as a time-averaged sound level with an averaging time of at least 30 s. Time-averaged sound
level may be measured directly or calculated from an indication of sound exposure level and
integration time. If time-averaged sound level cannot be determined, the time-weighted sound
level from the average of ten observations taken at random over a 60 s interval shall be
measured. If the time-weighted sound level is recorded, the S time weighting shall be used if
available; otherwise the F time weighting shall be used.
NOTE 1 The indication of sound level is influenced by background noise as well as the self-generated noise.
NOTE 2 The A-weighted level of self-generated noise is reported for information only and is not used to assess
conformance to a requirement. The level of self-generated noise is reported without an associated uncertainty.
11.2 Microphone replaced by the electrical input-signal device
With the microphone replaced by the electrical input-signal device (or using the specified
means of inserting electrical signals), and with the device terminated in the manner specified in
the Instruction Manual for measurements of the level of self-generated noise, the indicated
level of the time-averaged or time-weighted self-generated noise, measured by the same
procedure as with the microphone installed, shall be recorded and reported for all frequency
weightings and for the most-sensitive level range.
NOTE The level of self-generated noise is reported for information only and is not used to assess conformance to
a requirement. The level of self-generated noise is reported without an associated uncertainty.
12 Acoustical signal tests of a frequency weighting
12.1 The sound level meter shall be in the configuration submitted for periodic testing. The
sound level meter shall be set for frequency-weighting C, if available, otherwise for frequency-
weighting A. The frequency weighting shall be tested using a calibrated multi-frequency sound
calibrator, comparison coupler, electrostatic actuator, or a free-field facility. In the latter case,
the appropriate test procedure given in IEC 61672-2 shall be followed, but only for the test
frequencies specified in this clause. Evidence shall be available to demonstrate that the multi-
frequency sound calibrator conforms to the requirements of IEC 60942 for class 1
performance; a class 1/C multi-frequency sound calibrator may be used if appropriate for the
prevailing environmental conditions. The working standard microphone used with the
comparison coupler shall conform to the requirements of IEC 61094-4. The electrostatic
actuator shall conform to the applicable requirements of IEC 61094-6.
NOTE 1 Tests using a multi-frequency sound calibrator, comparison coupler, or electrostatic actuator, if the
appropriate free-field or random-incidence correction data are available, are likely to take less time than tests using
a free-field facility.
NOTE 2 A measurement microphone that conforms to the requirements of IEC 61094-1 for laboratory standard
microphones also conforms to the requirements of IEC 61094-4 for working standard microphones.
12.2 At each test frequency, data to correct the sound levels indicated by a sound level meter
to equivalent free-field or random-incidence sound levels determined in accordance with a
procedure given in IEC 62585 or IEC 61183, as applicable, shall be available. Correction data
shall account for:
61672-3  IEC:2013 – 11 –
– the equivalent free-field or random-incidence frequency response of the sound level meter
if the source of sound or simulated sound is the pressure field in a multi-frequency sound
calibrator, in a comparison coupler, or from an electrostatic actuator; and,
– if applicable, the average influence on the frequency response of a typical microphone of a
windscreen and any accessories that are part of the configuration of the sound level meter
for normal use.
12.3 Correction data shall be obtained from tables in the Instruction Manual for the sound
level meter.
12.4 If the necessary correction data are not available from the Instruction Manual, data from
the manufacturer of the microphone, multi-frequency sound calibrator, comparison coupler, or
electrostatic actuator may then be used. This data shall be publicly available.
NOTE It is possible that publicly available data that is not specified in the Instruction Manual has not been verified
according to IEC 61672-2.
12.5 The source for the free-field or random-incidence correction data shall be stated in the
documentation for the results of the periodic tests. The source for the associated uncertainties
of measurement shall be the same as the source for the corresponding correction data. If the
uncertainties of the corresponding free-field correction data are not available, the applicable
maximum-permitted uncertainties given in IEC 62585 shall be used in the calculation of the
laboratory’s total uncertainty budget.
12.6 If an accessory is part of the configuration for the normal use of the sound level meter
submitted for test but the relevant data on the influence of the accessory on the frequency
response of a typical microphone of the specified model are not available from the Instruction
Manual nor from the Internet website of the manufacturer or supplier of the sound level meter,
then periodic testing of the sound level meter cannot be performed in accordance with this part
of IEC 61672, except in a free-field facility.
12.7 The frequency weighting for tests with acoustical signals shall be determined at 125 Hz,
1 kHz, and 8 kHz.
12.8 At the discretion of the laboratory, the sound level meter shall be set to measure F-time-
weighted sound level or S-time-weighted sound level, or time-averaged sound level, or sound
exposure level. If sound exposure level is measured, the corresponding time-averaged sound
level shall be calculated as specified by IEC 61672-1 for the integration time. Averaging time or
integration time shall be at least 10 s and shall be recorded. The sound level meter shall be set
for the reference level range or the level range closest to the reference level range that will
permit displays of the signals from the multi-frequency sound calibrator, comparison coupler, or
electrostatic actuator. If necessary, the frequency weightings with acoustical signals shall be
tested in accordance with the free-field or random-incidence test procedure of IEC 61672-2, as
applicable.
12.9 For frequency-weighting tests using a multi-frequency sound calibrator, the sound
pressure level in the coupler of the sound calibrator shall preferably be set to the reference
sound pressure level at 1 kHz, but shall be in the range from 70 dB to 125 dB at all
frequencies. The sound pressure level produced in the coupler of the sound calibrator, when
coupled to the microphone of the sound level meter, shall be known by calibration at each test
frequency. If the correction data were determined with the protection grid of the microphone of
the sound level meter replaced with an adaptor ring, an adaptor ring of the same model shall
be used when performing the acoustical signal tests of the frequency weighting. If the
correction data were determined using a particular model of adaptor with the sound calibrator,
___________
This correction term includes the correction to equivalent free-field or random-incidence level for the source of
sound or simulated sound and the corrections for the typical effects of reflections from the case of the sound
level meter and for the effect of diffraction of sound around the microphone mounted on the sound level meter, as
applicable.
– 12 – 61672-3  IEC:2013
an adaptor of the same model shall be used when performing the acoustical signal tests of the
frequency weighting.
12.10 For frequency-weighting tests using a comparison coupler, the sound pressure level in
the coupler shall preferably be set to the reference sound pressure level at 1 kHz, but shall be
in the range from 70 dB to 125 dB at all frequencies. The sound pressure level produced in the
coupler shall be known by calibration at each test frequency. If the correction data were
determined with the protection grid of the microphone of the sound level meter replaced with an
adaptor ring, an adaptor ring of the same model shall be used when performing the acoustical
signal tests of the frequency weighting. If the correction data were determined using a
particular model of adaptor with the comparison coupler, an adaptor of the same model shall
be used when performing the acoustical signal tests of the frequency weighting.
12.11 For frequency-weighting tests using an electrostatic actuator, the electrostatic actuator
shall be coupled to the microphone in accordance with the instructions of the manufacturer of
the device and also with the instructions of the manufacturer of the microphone installed on the
sound level meter, if available. The signal voltage applied to the electrostatic actuator shall be
adjusted to display an indicated sound level between 70 dB and 100 dB at 1 kHz.
NOTE At frequencies less than 1 kHz, the measured frequency weighting when using an electrostatic actuator will
not show the effects of defects such as holes in the diaphragm of the microphone.
12.12 The sound calibrator and microphone, comparison coupler and microphones, or
electrostatic actuator and microphone shall be coupled and allowed an appropriate time to
stabilize. The sound level displayed in response to the input signals shall be recorded for each
test frequency. As a minimum, two repetitions of the coupling and measurements shall be
performed to give a total of at least three tests.
12.13 At each test frequency, the average sound level shall be calculated as the arithmetic
average of the adjusted indications of frequency-weighted sound level.
12.14 At each test frequency, for tests using a multi-frequency sound calibrator, comparison
coupler, or electrostatic actuator, the average sound level from 12.13 shall be corrected to an
equivalent free-field or random-incidence frequency-weighted sound level by application of the
applicable correction data noted in 12.2.
12.15 The relative frequency weighting, relative to the response at 1 kHz, shall be determined
from the average equivalent free-field or random-incidence sound level at a test frequency
minus the average equivalent free-field or random-incidence sound level at 1 kHz.
12.16 Measured deviations of the relative frequency weighting from the corresponding design
goals given in IEC 61672-1 shall not exceed the applicable acceptance limits from
IEC 61672-1.
13 Electrical signal tests of frequency weightings
13.1 Frequency weightings shall be determined using steady sinusoidal electrical input
signals for all frequency weightings for which design goals and acceptance limits are specified
in IEC 61672-1 and which are provided in the sound level meter. The sound level meter shall
be set to display F-time-weighted sound level, time-averaged sound level, or sound exposure
level. If sound exposure level is measured, the corresponding time-averaged sound level shall
be calculated as specified by IEC 61672-1 for the integration time. Averaging time or
integration time shall be at least 10 s and shall be recorded.
13.2 On the reference level range and for each frequency weighting to be tested, the level of
a 1 kHz input signal shall be adjusted to yield an indication that is 45 dB less than the upper
boundary stated in the Instruction Manual for the linear operating range at 1 kHz on the
reference level range. The input signal level shall be recorded.

61672-3  IEC:2013 – 13 –
13.3 At test frequencies other than 1 kHz, the level of the input electrical signal shall be
determined as the level of the input signal at 1 kHz minus the exact design-goal response,
given in IEC 61672-1 for the selected frequency weighting at the test frequency. The indication
on the display device shall be recorded.
13.4 The levels of the input signals and th
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