IEC 61672-1:2013

IEC 61672-1 ®
Edition 2.0 2013-09
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Electroacoustics – Sound level meters –
Part 1: Specifications
Electroacoustique – Sonomètres –
Partie 1: Spécifications
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IEC 61672-1 ®
Edition 2.0 2013-09
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Electroacoustics – Sound level meters –

Part 1: Specifications
Electroacoustique – Sonomètres –

Partie 1: Spécifications
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX XA
ICS 17.140.50 ISBN 978-2-8322-1087-1

– 2 – 61672-1 © IEC:2013
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 8
3 Terms and definitions . 8
4 Reference environmental conditions . 14
5 Performance specifications . 14
5.1 General . 14
5.2 Adjustments at the calibration check frequency . 17
5.3 Corrections to indicated levels . 17
5.3.1 General . 17
5.3.2 Reflections and diffraction . 17
5.3.3 Windscreens . 18
5.3.4 Format for correction data . 18
5.3.5 Corrections for use during periodic testing . 19
5.4 Directional response . 19
5.5 Frequency weightings . 20
5.6 Level linearity . 23
5.7 Self-generated noise . 24
5.8 Time-weightings F and S . 24
5.9 Toneburst response . 24
5.10 Response to repeated tonebursts . 26
5.11 Overload indication . 27
5.12 Under-range indication . 27
5.13 C-weighted peak sound level . 27
5.14 Stability during continuous operation . 28
5.15 High-level stability . 28
5.16 Reset . 29
5.17 Thresholds . 29
5.18 Display . 29
5.19 Analogue or digital output . 29
5.20 Timing facilities . 30
5.21 Radio frequency emissions and disturbances to a public power supply . 30
5.22 Crosstalk . 31
5.23 Power supply . 31
6 Environmental, electrostatic, and radio-frequency requirements . 32
6.1 General . 32
6.2 Static pressure . 32
6.3 Air temperature . 32
6.4 Humidity . 33
6.5 Electrostatic discharge . 33
6.6 A.C. power-frequency and radio-frequency fields . 33
6.7 Mechanical vibration . 34
7 Provision for use with auxiliary devices . 35
8 Marking . 35
9 Instruction Manual . 35

61672-1 © IEC:2013 – 3 –
9.1 General . 35
9.2 Information for operation . 36
9.2.1 General . 36
9.2.2 Design features . 36
9.2.3 Power supply . 37
9.2.4 Adjustments at the calibration check frequency . 37
9.2.5 Corrections to indicated levels . 37
9.2.6 Operating the sound level meter . 37
9.2.7 Accessories . 38
9.2.8 Influence of variations in environmental conditions . 38
9.3 Information for testing . 39
Annex A (informative) Relationship between tolerance interval, corresponding
acceptance interval and the maximum-permitted uncertainty of measurement . 41
Annex B (normative) Maximum-permitted uncertainties of measurement . 42
Annex C (informative) Example assessments of conformance to specifications of this
standard . 44
Annex D (normative) Frequencies at fractional-octave intervals . 47
Annex E (normative) Analytical expressions for frequency-weightings C, A, and Z . 49

Figure 1 – Principal steps involved in forming a time-weighted sound level . 10
Figure A.1 – Relationship between tolerance interval, corresponding acceptance
interval and the maximum-permitted uncertainty of measurement . 41
Figure C.1 – Examples of assessment of conformance . 46

Table 1 – Acceptance limits for the difference between a measured windscreen
correction and the corresponding correction given in the Instruction Manual . 18
Table 2 – Acceptance limits for deviations of directional response from the design goal . 20
Table 3 – Frequency weightings and acceptance limits . 22
Table 4 – Reference 4 kHz toneburst responses and acceptance limits . 25
Table 5 – Reference differences for C-weighted peak sound levels and acceptance
limits . 28
Table 6 – Limits for conducted disturbance to the voltage of a public supply of electric
power . 31
Table B.1 – Maximum-permitted uncertainties of measurement for a coverage
probability of 95 % . 42
Table C.1 – Examples of assessment of conformance . 45
Table D.1 – Frequencies at one-third-octave intervals . 47
Table D.2 – Frequencies at one-sixth-octave intervals . 48
Table D.3 – Frequencies at one-twelfth-octave intervals . 48

– 4 – 61672-1 © IEC:2013
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ELECTROACOUSTICS –
SOUND LEVEL METERS –
Part 1: Specifications
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
misinterpretation by any end user.
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
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
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 61672-1 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 2002. This second
edition constitutes a technical revision.
The main technical changes with respect 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 %.

61672-1 © IEC:2013 – 5 –
The text of this second edition is based on that of the first edition and the following
documents:
FDIS Report on voting
29/812/FDIS 29/823/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 of 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.
– 6 – 61672-1 © IEC:2013
INTRODUCTION
For assessments of conformance to performance specifications, this second edition of
IEC 61672-1 uses different criteria than were used for the 2002 first edition.
In the period from 1961 to 1985, International Standards for sound level meters did not
provide any requirements or recommendations to account for the uncertainty of measurement
in assessments of conformance to specifications.
This absence of requirements or recommendations to account for uncertainty of measurement
created ambiguity in determinations of conformance to specifications for situations where a
measured deviation from a design goal was close to a limit of the allowed deviation. If
conformance was determined based on whether a measured deviation did or did not exceed
the limits, the end-user of the sound level meter incurred the risk that the true deviation from
a design goal exceeded the limits.
To remove this ambiguity, IEC Technical Committee 29, at its meeting in 1996, adopted a
policy to account for measurement uncertainty in assessments of conformance in International
Standards that it prepares.
The first edition (2002) of IEC 61672-1 accounted for measurement uncertainty by giving two
explicit criteria for determining conformance to the specifications. The two criteria were (a)
that measured deviations from design goals, extended by the expanded uncertainty of
measurement, do not exceed the applicable tolerance limits and (b) that the expanded
uncertainty of measurement does not exceed agreed-upon maximum values. For most
performance specifications, the tolerance limits were calculated essentially by extending the
allowances for design and manufacturing from the 1979 and 1985 International Standards for
sound level meters by the applicable maximum-permitted expanded uncertainties of
measurement. Tolerance limits were intended to represent the limits for true deviations from
design goals with a coverage probability of 95 %.
This second edition of IEC 61672-1 uses an amended criterion for assessing conformance to
a specification. Conformance 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. Acceptance limits are
analogous to the allowances for design and manufacturing implied in the first edition (2002) of
IEC 61672-1. Actual and maximum-permitted uncertainties are determined for a coverage
probability of 95 %. The amended criterion for assessing conformance does not necessitate
any change to the design of a sound level meter in order to conform to the specifications of
this International Standard.
The maximum-permitted uncertainties of measurement are not equivalent to the uncertainties
associated with the measurement of a sound level. The uncertainty of a measured sound level
is evaluated from the anticipated deviations of the electroacoustical performance of the sound
level meter from the relevant design goals as well as estimates of the uncertainties
associated with the specific measurement situation. Unless more-specific information is
available, the evaluation of the contribution of a specific sound level meter to a total
measurement uncertainty can be based on the acceptance limits and maximum-permitted
uncertainties specified in this standard.

61672-1 © IEC:2013 – 7 –
ELECTROACOUSTICS –
SOUND LEVEL METERS –
Part 1: Specifications
1 Scope
This part of IEC 61672 gives electroacoustical performance specifications for three kinds of
sound measuring instruments:
• a time-weighting sound level meter that measures exponential-time-weighted, frequency-
weighted sound levels;
• an integrating-averaging sound level meter that measures time-averaged, frequency-
weighted sound levels; and
• an integrating sound level meter that measures frequency-weighted sound exposure
levels.
Sound level meters conforming to the requirements of this standard have a specified
frequency response for sound incident on the microphone from one principal direction in an
acoustic free field or successively from random directions.
Sound level meters specified in this standard are intended to measure sounds generally in the
range of human hearing.
NOTE The AU frequency weighting specified in IEC 61012 can be applied for measurements of A-weighted sound
levels of audible sound in the presence of a source that contains spectral components at frequencies greater than
20 kHz.
Two performance categories, class 1 and class 2, are specified in this standard. In general,
specifications for class 1 and class 2 sound level meters have the same design goals and
differ mainly in the acceptance limits and the range of operational temperature. Acceptance
limits for class 2 are greater than, or equal to, those for class 1.
This standard is applicable to a range of designs for sound level meters. A sound level meter
may be a self-contained hand-held instrument with an attached microphone and a built-in
display device. A sound level meter may be comprised of separate components in one or
more enclosures and may be capable of displaying a variety of acoustical signal levels. Sound
level meters may include extensive analogue or digital signal processing, separately or in
combination, with multiple analogue and digital outputs. Sound level meters may include
general-purpose computers, recorders, printers, and other devices that form a necessary part
of the complete instrument.
Sound level meters may be designed for use with an operator present or for automatic and
continuous measurements of sound level without an operator present. Specifications in this
standard for the response to sound waves apply without an operator present in the sound
field.
___________
IEC 61012, Filters for the measurement of audible sound in the presence of ultrasound.

– 8 – 61672-1 © IEC:2013
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 61000-4-2:2008, Electromagnetic compatibility (EMC) – Part 4-2: Testing and
measurement techniques – Electrostatic discharge immunity test
IEC 61000-6-2:2005, Electromagnetic compatibility (EMC) – Part 6-2: Generic standards –
Immunity for industrial environments
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
IEC 62585, Electroacoustics – Methods to determine corrections to obtain the free-field
response of a sound level meter
ISO/IEC Guide 98-4:2012, Evaluation of measurement data – The role of measurement
uncertainty in conformance assessment
ISO/IEC Guide 99, International vocabulary of metrology – Basic and general concepts and
associated terms (VIM)
CISPR 16-1-1:2010, Specification for radio disturbance and immunity measuring apparatus
and methods – Part 1-1: Radio disturbance and immunity measuring apparatus – Measuring
apparatus
Amendment 1:2010
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO/IEC Guide 98-4,
ISO/IEC Guide 99, and IEC 61000-6-2, as well as the following apply.
NOTE All quantities are expressed in SI units.
3.1
sound pressure
difference between an instantaneous total pressure and the corresponding static pressure
Note 1 to entry: Sound pressure is expressed in pascals (Pa).
3.2
sound pressure level
ten times the logarithm to the base 10 of the ratio of the time-mean-square of a sound-
pressure signal to the square of the reference value
___________
CISPR = International Special Committee on Radio Interference.

61672-1 © IEC:2013 – 9 –
Note 1 to entry: Sound pressure level is expressed in decibels (dB).
Note 2 to entry: The reference value is 20 μPa.
3.3
frequency weighting
difference, as a specified function of frequency, between the level of the frequency-weighted
signal indicated on the display device and the corresponding level of a constant-amplitude
sinusoidal input signal
Note 1 to entry: Level difference is expressed in decibels (dB).
3.4
time weighting
exponential function of time, of a specified time constant, that weights the square of a sound-
pressure signal
3.5
sound level
frequency-weighted sound pressure level
level with time weighting or time averaging of the square of a frequency-weighted sound-
pressure signal
Note 1 to entry: Sound level is expressed in decibels (dB).
3.6
time-weighted sound level
ten times the logarithm to the base 10 of the ratio of the running time average of the time-
weighted square of a frequency-weighted sound-pressure signal to the square of the
reference value
Note 1 to entry: Time-weighted sound level is expressed in decibels (dB).
Note 2 to entry: For time-weighted sound level, example letter symbols are L , L , L , and L for frequency
AF AS CF CS
weightings A and C and time weightings F and S.
Note 3 to entry: In symbols and as an example, A-weighted and F-time-weighted sound level L (t) at observation
AF
time t can be represented by
t
 2 −−(t ξτ)/ 
F
1/ τ peξ dξ
( ) ( )
FA
∫
 −∞ 
Lt( ) = 10 lg dB (1)
AF
 2 
p
 
 
where
– τ is the exponential time constant in seconds for the F time weighting;
F
– ξ is a dummy variable of time integration from some time in the past, as indicated by -∞ for the lower limit of
the integral, to the time of observation t;
– p (ξ) is the A-weighted instantaneous sound-pressure signal; and
A
– p is the reference value of 20 μPa.
Note 4 to entry: The sketch in Figure 1 illustrates the process indicated by Equation (1).
a b c d e
IEC  2243/13
Key
a Start with a frequency-weighted electrical input signal
b Square the input signal
c Apply a low-pass filter with one real pole at -1/τ (exponential time weighting)
d Take the base-10 logarithm
e Display the result in decibels with the square of a reference value of 20 μPa

– 10 – 61672-1 © IEC:2013
Figure 1 – Principal steps involved in forming a time-weighted sound level
3.7
maximum time-weighted sound level
greatest time-weighted sound level within a stated time interval
Note 1 to entry: Maximum time-weighted sound level is expressed in decibels (dB).
Note 2 to entry: Example letter symbols for maximum time-weighted sound level are L , L , L , and
AFmax ASmax CFmax
L for frequency weightings A and C and time weightings F and S.
CSmax
3.8
peak sound pressure
greatest sound pressure (positive or negative) during a stated time interval
Note 1 to entry: Peak sound pressure is expressed in pascals (Pa).
Note 2 to entry: A peak sound pressure can arise from a positive or negative instantaneous sound pressure.
3.9
peak sound level
ten times the logarithm to the base 10 of the ratio of the square of a frequency-weighted peak
sound-pressure signal to the square of the reference value
Note 1 to entry: Peak sound level is expressed in decibels (dB).
Note 2 to entry: The reference value is 20 μPa.
3.10
time-averaged sound level
equivalent continuous sound level
ten times the logarithm to the base 10 of the ratio of the time average of the square of a
frequency-weighted sound-pressure signal during a stated time interval to the square of the
reference value
Note 1 to entry: Time-averaged or equivalent continuous sound level is expressed in decibels (dB).
Note 2 to entry: In symbols and as an example, time-averaged, A-weighted sound level L is given by
,
Aeq,T
t

(1/Tp) (ξξ)d
A
∫
tT−

L = 10 lg dB
(2)
Aeq,T

p


where
– ξ is a dummy variable of time integration over the averaging time interval ending at the time of observation t;
– T is the averaging time interval;
– p (ξ) is the A-weighted sound-pressure signal; and
A
– p is the reference value of 20 μPa.
Note 3 to entry: In principle, time weighting is not involved in a determination of time-averaged sound level.
3.11
sound exposure
time integral of the square of a frequency-weighted sound-pressure signal over a stated time
interval or event of stated duration
Note 1 to entry: Duration of integration is included implicitly in the time integral and is not always reported
explicitly, although it is useful to state the nature of the event. For measurements of sound exposure over a
specified time interval, duration of integration is usually reported and indicated by a suitable subscript to the letter
symbol, for example as E .
A,1h
Note 2 to entry: In symbols and as an example, A-weighted sound exposure E is represented by
A,T
61672-1 © IEC:2013 – 11 –
t
(3)
E = pt( )dt
A,T A
∫
t
where pt() is the square of the A-weighted sound-pressure signal during integration time T starting at t1 and
A
ending at t .
Note 3 to entry: The unit of sound exposure is pascal-squared seconds (Pa s) if sound pressure is in pascals and
running time is in seconds.
Note 4 to entry: For applications such as measurement of exposure to noise in the workplace, sound exposure in
pascal-squared hours is more convenient than pascal-squared seconds.
3.12
sound exposure level
ten times the logarithm to the base 10 of the ratio of a sound exposure to the reference value
Note 1 to entry: Sound exposure level is expressed in decibels (dB).
Note 2 to entry: In symbols and as an example, A-weighted sound exposure level L is related to the
AE,T
corresponding time-averaged, A-weighted sound level L by
Aeq,T
t
2
p (tt)d
A
∫  E  
T
t
A,T
(4)
L = 10 lg dBL= 10 lg dB =+ 10 lg dB
  
AET, Aeq,T
2
ET
pT
 00 


where
– E is the A-weighted sound exposure in pascal-squared seconds over time interval T (see Equation (3));
A,T
2 -12 2
pT =
– E is the reference value given by (20 μPa) × (1 s) = 400×10 Pa s;
– T is the measurement time interval, in seconds, starting at t and ending at t , and
1 2
– T is the reference value of 1 s for sound exposure level.
Note 3 to entry: Time-averaged, A-weighted sound level L during averaging time interval T is related to the
Aeq,T
corresponding A-weighted sound exposure E , or the A-weighted sound exposure level L , occurring within
A,T AE,T
that interval by
0,1L
Aeq,T
(5)
E = pT 10
A,T 0 ( )
or

E 
T
A,T
(6)
LL= 10 lg  dB =− 10 lg dB

Aeq,T AET,

T
pT
0

3.13
microphone
electroacoustic transducer by which electrical signals are obtained from acoustic oscillations
[SOURCE: IEC 60050-801:1994, definition 801-26-01]
3.14
microphone reference point
point specified on, or close to, the microphone to describe the position of the microphone
Note 1 to entry: The microphone reference point can be at the centre of the diaphragm of the microphone.
3.15
reference direction
inward direction toward the microphone reference point and specified for determining the
directional response and frequency weighting of a sound level meter
Note 1 to entry: The reference direction can be specified with respect to an axis of symmetry.

– 12 – 61672-1 © IEC:2013
3.16
sound-incidence angle
angle between the reference direction and a line between the acoustic centre of a sound
source and the microphone reference point
Note 1 to entry: Sound-incidence angle is expressed in degrees.
3.17
relative directional response
for any frequency weighting and at any frequency of incident sinusoidal sounds, and in a
specified plane containing the principal axis of the microphone, sound level indicated at a
given sound-incidence angle minus the sound level indicated for sound at the same frequency
from the same source and incident from the reference direction
Note 1 to entry: Relative directional response is expressed in decibels.
3.18
directivity factor
for a sound level meter, a measure of the deviation from an ideal directional response with
equal sensitivity at all possible angles of sound incidence on the microphone
Note 1 to entry: Directivity factor is non-dimensional.
3.19
directivity index
ten times the base-ten logarithm of the directivity factor
Note 1 to entry: Directivity index is expressed in decibels.
3.20
relative frequency-weighted free-field response
for a given frequency, time-weighted or time-averaged, frequency-weighted sound level
indicated by a sound level meter in response to plane progressive sinusoidal sound incident
on the microphone from the reference direction minus the corresponding time-weighted or
time-averaged sound level present at the position of the microphone reference point for the
sound level meter and from the same sound source but in the absence of the sound level
meter
Note 1 to entry: Relative frequency-weighted free-field response is expressed in decibels (dB).
Note 2 to entry: Relative frequency-weighted free-field response is called free-field sensitivity level in IEC 61183.
3.21
relative frequency-weighted random-incidence response
for a given frequency, time-averaged, frequency-weighted sound level indicated by a sound
level meter in response to random-incidence sound minus the time-averaged sound pressure
level present at the position of the microphone reference point for the sound level meter and
from the same sound source but in the absence of the sound level meter
Note 1 to entry: Relative frequency-weighted random-incidence response is expressed in decibels (dB).
Note 2 to entry: Relative frequency-weighted random-incidence response is called random-incidence sensitivity
level in IEC 61183.
3.22
level range
range of nominal sound levels measured for a particular setting of the controls of a sound
level meter
Note 1 to entry: Level range is expressed in decibels (dB), for example, the 50 dB to 110 dB range.

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3.23
reference sound pressure level
sound pressure level specified for testing the electroacoustic performance of a sound level
meter
Note 1 to entry: Reference sound pressure level is expressed in decibels (dB).
3.24
reference level range
level range specified for testing the electroacoustic characteristics of a sound level meter and
containing the reference sound pressure level
Note 1 to entry: Reference level range is expressed in decibels (dB), for example, the 50 dB to 110 dB range.
3.25
calibration check frequency
nominal frequency of the sinusoidal sound pressure produced by a sound calibrator
3.26
level linearity deviation
at a stated frequency, an indicated signal level minus the anticipated signal level
Note 1 to entry: Level linearity deviation is expressed in decibels (dB).
3.27
linear operating range
on any level range and at a stated frequency, the range of sound levels over which level
linearity deviations do not exceed the applicable acceptance limits specified in this standard
Note 1 to entry: Linear operating range is expressed in decibels (dB).
3.28
total range
range of A-weighted sound levels, in response to sinusoidal signals, from the smallest sound
level, on the most-sensitive level range, to the greatest sound level, on the least-sensitive
level range, that can be measured without indication of overload or under-range and without
exceeding the acceptance limits specified in this standard for level linearity deviation
Note 1 to entry: Total range is expressed in decibels (dB).
3.29
toneburst
one or more complete cycles of a sinusoidal electrical signal starting and stopping at a zero
crossing of the waveform
3.30
toneburst response
maximum time-weighted sound level, or sound exposure level, measured in response to a
toneburst minus the corresponding measured sound level of the steady input signal from
which the toneburst was extracted
Note 1 to entry: Toneburst response is expressed in decibels (dB).
3.31
reference orientation
orientation of a sound level meter for tests to demonstrate conformance to the specifications
of this standard for emissions of, and immunity to the effects of exposure to, radio-frequency
fields
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3.32
coverage probability
probability that the set of true quantity values of a measurand is contained within a specified
coverage interval
[SOURCE: ISO/IEC Guide 98-4:2012, definition 3.2.8]
3.33
acceptance limit
specified upper or lower bound of permissible measured quantity values
[SOURCE: ISO/IEC Guide 98-4:2012, definition 3.3.8]
4 Reference environmental conditions
Reference environmental conditions for specifying the electroacoustic performance of a sound
level meter are:
• air temperature 23 °C;
• static pressure 101,325 kPa;
• relative humidity 50 %.
5 Performance specifications
5.1 General
5.1.1 Generally, a sound level meter is a combination of a microphone, a preamplifier, a
signal processor, and a display device. Performance specifications of this standard apply to
any design for microphone and preamplifier that is appropriate for a sound level meter.
The signal processor includes the combined functions of an amplifier with a specified and
controlled frequency response, a device to form the square of the frequency-weighted, time-
varying sound-pressure signal, and a time integrator or time averager. Signal processing that
is necessary to conform to the specifications of this standard is an integral part of a sound
level meter.
In this standard, a display device provides a physical and visible display, or storage, of
measurement results. Any stored measurement result shall be available for display by means
of a manufacturer-specified device, for instance a computer with associated software.
5.1.2 Performance specifications of this Clause apply under the reference environmental
conditions of Clause 4.
5.1.3 For specifying the maximum-permitted emission of, and immunity to the effects of
exposure to, radio-frequency fields, sound level meters are classified into three groups as
follows:
– group X sound level meters: self-contained instruments that include sound level
measurement facilities according to this standard and which specify internal battery power
for the normal mode of operation, requiring no external connections to other apparatus to
measure sound levels;
– group Y sound level meters: self-contained instruments that include sound level
measurement facilities according to this standard and which specify connection to a public
supply of electric power for the normal mode of operation, requiring no external
connections to other apparatus to measure sound levels; and

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– group Z sound level meters: instruments that include sound level measurement facilities
according to this standard and which require two or more items of equipment, which are
essential constituent parts of the sound level meter, to be connected together by some
means for the normal mode of operation. The separate items may be operated from
internal batteries or from a public supply of electric power.
5.1.4 The configuration of the complete sound level meter and its normal mode of
operation shall be stated in the Instruction Manual. If appropriate, the configuration of the
complete sound level meter includes a windscreen and other devices that are installed around
the microphone as integral components for the normal mode of operation.
5.1.5 A sound level meter that is stated in the Instruction Manual to be a class 1 or class 2
sound level meter shall conform to all relevant class 1 or class 2 specifications, respectively,
that are provided in this standard. A class 2 sound lev
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