ASTM E1686-23

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E1686 − 23
Standard Guide for
Applying Environmental Noise Measurement Methods and
Criteria
This standard is issued under the fixed designation E1686; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope guidance. Users needing further general background on sound
and sound measurement are directed to the books listed in the
1.1 This guide covers many measurement methods and
References section.
criteria for evaluating environmental noise, some of which are
1.4 Criteria in Regulations—Certain criteria are specified to
required to be used for specific purposes by governmental
regulations. It is intended to provide users who may not be be used by government regulation, law, or ordinance for
specific purposes. Any investigation or evaluation of a com-
familiar with them with an overview of the wide variety of
available methods and criteria. It includes the following: munity noise issue must start with identifying applicable
regulations and evaluating compliance with them. This docu-
1.1.1 The use of weightings, penalties, and adjustment or
ment discusses but is not limited to regulations and ordinances.
normalization factors;
Due to the wide variation in local regulations, those are
1.1.2 Types of noise measurements and criteria, indicating
discussed more generally, and specific criteria are provided
their limitations and best uses;
only from national government regulations. Regulations typi-
1.1.3 Sources of criteria;
cally specify measurement methods and criteria for purposes of
1.1.4 Recommended procedures for criteria selection;
the regulation. Local ordinances must be written for ease of
1.1.5 A catalog of sources of selected available criteria; and
enforcement and cannot address all situations satisfactorily
1.1.6 Suggested applications of sound level measurements
without becoming too complex. Such ordinances are also often
and criteria.
prepared without competent guidance and can be too restrictive
1.2 Criteria Selection—Thorough evaluation of noise issues
in some cases and not restrictive enough in others. Other
requires consideration of many characteristics of both the
regulations that determine government spending for noise
sound and the environment into which it is introduced. This
control must balance that cost to the general public against
guide will assist users in selecting criteria for the following:
impacts on individuals.
1.2.1 Evaluating the effect of existing or potential outdoor
1.5 This standard does not purport to address all of the
sounds on a community considering the magnitude and other
safety concerns, if any, associated with its use. It is the
characteristics of the sound and environment;
responsibility of the user of this standard to establish appro-
1.2.2 Establishing or revising local noise ordinances, codes,
priate safety, health, and environmental practices and deter-
or bylaws, including performance standards in zoning regula-
mine the applicability of regulatory limitations prior to use.
tions; and
1.6 This international standard was developed in accor-
1.2.3 Identifying and evaluating compliance with regulatory
dance with internationally recognized principles on standard-
requirements that do not specify an acoustical measurement
ization established in the Decision on Principles for the
method or criterion or which are unclear.
Development of International Standards, Guides and Recom-
1.3 Reasons for Criteria—This guide discusses the many mendations issued by the World Trade Organization Technical
reasons for noise criteria, ways sound can be measured and Barriers to Trade (TBT) Committee.
specified, and advantages and disadvantages of the most
2. Referenced Documents
widely used types of criteria. The guide refers the user to
appropriate documents for more detailed information and
2.1 ASTM Standards:
C634 Terminology Relating to Building and Environmental
Acoustics
This guide is under the jurisdiction of ASTM Committee E33 on Building and
Environmental Acoustics and is the direct responsibility of Subcommittee E33.09 on
Community Noise. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Nov. 1, 2023. Published December 2023. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 1995. Last previous edition approved in 2016 as E1686 – 16. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/E1686-23. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1686 − 23
E966 Guide for Field Measurements of Airborne Sound IEC 61672-1: 2013 Electroacoustics – Sound level meters –
Attenuation of Building Facades and Facade Elements Part 1: Specifications
E1014 Guide for Measurement of Outdoor A-Weighted
2.5 DIN Standard:
Sound Levels DIN 45692 Measurement technique for the simulation of
E1503 Test Method for Conducting Outdoor Sound Mea-
auditory sensation of sharpness (in German)
surements Using a Statistical Sound Analysis System 2.6 United States Military Standard:
2.2 ASA/ANSI Standards:
MIL STD 1474E Department of Defense Design Criteria
ASA/ANSI S1.1 Acoustical Terminology Standard Noise Limits
ASA/ANSI S1.4/Part 1/IEC 61672-1 Electroacoustics –
3. Terminology
Sound Level Meters – Part 1: Specifications
ASA/ANSI S1.4-1983 Specifications for Sound Level Me-
3.1 General—This guide provides guidance for various
ters
measurement methods and criteria initially defined in other
ASA/ANSI S1.11/Part 1/IEC 61260-1 Electroacoustics –
documents. Most acoustical terms used in this standard are
Octave-Band and Fractional-Octave-Band Filters – Part 1:
defined in either Terminology C634 or within this standard
Specifications
with their abbreviations and symbols for use in equations. The
ASA/ANSI S1.13 Measurement of Sound Pressure Levels in
definition of terms explicitly given within this standard take
Air
precedence over definitions given in Terminology C634. For
ANSI S1.43 Specifications for Integrating-Averaging Sound
interpretation of this document, the definitions within Termi-
Level Meters
nology C634 and this standard take precedence over any other
ASA/ANSI S3.4 Procedure for the Computation of Loud-
definitions of defined terms found in any other documents,
ness of Steady Sounds
including other documents that are referenced in this standard.
ASA/ANSI S3.14 Rating Noise with Respect to Speech
3.2 Definitions of Terms Specific to This Standard:
Interference
3.2.1 community noise equivalent level, CNEL, (dB), n—see
ASA/ANSI S12.4 Method for Assessment of High-Energy
day-evening-night average sound level.
Impulsive Sounds with Respect to Residential Communi-
3.2.2 day-evening-night average sound level, DENL, (dB),
ties
L —where * is a letter denoting the frequency weighting
*den
ASA/ANSI S12.7 Methods for Measurement of Impulse
(understood to be A if deleted), (dB), n—a time-average sound
Noise
level computed for an average calendar day period with the
ASA/ANSI S12.9 Quantities and Procedures for Description
addition of 4.77 dB or 5 dB to all levels between 7:00 pm and
and Measurement of Environmental Sound – Part 1: Basic
10:00 pm, and 10 dB to all levels after 10:00 pm and before
Quantities and Definitions; Part 2: Measurement of Long-
7:00 am. A-weighting is understood unless clearly stated
Term, Wide-Area Sound; Part 3: Short Term Measure-
otherwise.
ments with an Observer Present; Part 4: Noise Assessment
3.2.2.1 Discussion—Various standards and regulations de-
and Prediction of Long-Term Community Response; Part
fine both CNEL and DENL differently in terms of the level
5: Sound Level Descriptors for Determination of Compat-
added to sound during the evening period. Earliest definitions
ible Land Use
indicated the average acoustic energy was to be multiplied by
ASA/ANSI S12.65 Rating Noise with Respect to Speech
3 which is equivalent to a 4.77 dB addition, but some more
Interference
recent documents define the quantity with a 5 dB addition. In
ASA/ANSI S12.100 Methods to Define and Measure the
critical situations, the definition in a particular regulation or
Residual Sound in Protected Natural and Quiet Residen-
standard should be used.
tial Areas
2.3 ISO Standards: 3.2.3 day-night average sound level, DNL, L* —where * is
dn
a letter denoting the frequency weighting (understood to be A
ISO 532-1 Acoustics — Methods for calculating loudness —
Part 1: Zwicker method if deleted), (dB), n—a time-average sound level computed for
an average calendar day period with the addition of 10 dB to all
ISO 532-2 Acoustics — Methods for calculating loudness —
Part 2: Moore-Glasberg method sound after 10:00 pm and before 7:00 am. A-weighting is
understood unless clearly stated otherwise.
ISO 1996-1:2016 Acoustics — Description, measurement
and assessment of environmental noise — Part 1: Basic
3.2.4 loudness, (sone), n—that attribute of sound sensation
quantities and assessment procedures
for which sounds may be described on a scale from soft to loud
2.4 IEC Standards:
or by a value in sones calculated from measured data.
IEC 61260-1 Electroacoustics – Octave-band and fractional-
3.2.4.1 Discussion—– One sone is the perceived loudness of
octave-band filters – Part 1: Specifications
a 1000 Hz tone of 40 dB sound pressure level. A sound that is
IEC 61672-1: 2002 Electroacoustics – Sound level meters –
n times as loud is n sones.
Part 1: Specifications
Available from Beuth Verlag GmbH (DIN-- DIN Deutsches Institut fur
Available from American National Standards Institute (ANSI), 25 W. 43rd St., Normung e.V.), Burggrafenstrasse 6, 10787, Berlin, Germany, http://www.en.din.de.
4th Floor, New York, NY 10036, http://www.ansi.org.
4 6
Available from International Electrotechnical Commission (IEC), 3 rue de Available from DLA Document Services, Building 4/D, 700 Robbins Ave.,
Varembé, Case postale 131, CH-1211, Geneva 20, Switzerland, http://www.iec.ch. Philadelphia, PA 19111-5094, http://quicksearch.dla.mil.
E1686 − 23
3.2.5 normalization, n—as applied to the evaluation of otherwise, A-weighting will be understood. The unit for time in
noise in communities, the practice of adjusting a measured the ratio shall be stated, for example, as seconds or minutes per
sound level to compare to criteria that are based on conditions hour or day. ASA/ANSI S12.9, Part 1
different from those present at the time or location of the 3.2.11 time weighting, n—the exponential averaging of a
measurement. time varying signal with a specified time constant.
3.2.5.1 Discussion—This term originated in methods devel- 3.2.11.1 Discussion—Exponential time weightings are ap-
oped in the 1950’s and was adopted by the US Environmental plied to sound signals to obtain measurements of a sound level
Protection Agency. Some current standards use the word at a specific time that has not been time-averaged. The two
“adjustment” for the same concept. currently standardized time weightings are “slow” with a time
constant of 1 s and “fast” with a time constant of ⁄8 s.
3.2.6 residual sound, n—the all-encompassing sound, being
usually a composite of sound from many sources from many
3.3 Index of Terms—The following commonly used terms
directions, near and far, remaining at a given position in a
are discussed in the sections referenced in this guide.
given situation when all uniquely identifiable discrete sound
Term Paragraph
sources of particular interest or considered an interference, A-weighting 6.2
C-weighting 6.2
whether steady or intermittent, are eliminated, rendered
community noise equivalent level 8.5.3
insignificant, or otherwise not included.
community tolerance level 8.5.2
3.2.6.1 Discussion—Residual sound is distinguished from day-evening-night average sound level 8.5.3
day-night average sound level 8.5.2
background noise (which by definition also includes the
equivalent level 6.5 and 8.5.1
self-noise of measurement systems), and from ambient noise
fast, time weighting or sound level 6.3
which includes all sound present. It is also distinguished from impulse, time weighting or sound level 6.3
loudness 8.11
a steady sound that is dominant between discrete events. The
maximum sound level 8.3
specific sounds excluded from the residual sounds should be
normalization or adjustment of DNL 7.4
octave band, or one-third octave band 6.6 and 8.9
identified. If the excluded sound is intermittent (such that it is
peak sound pressure level 6.4 and 8.4
on and off for periods), the residual sound may be approxi-
percentile level 8.6
mated by the L90. If an excluded sound is steady and there are
slow, time weighting or sound level 6.3
intermittent events, the L90 can be used to approximate the sound exposure level 8.5.4
speech interference level 8.10
level of such steady sound and the residual sound must be
time above 8.7
measured with the steady source not operating or approximated
time-average sound level 6.5 and 8.5.1
by a measurement at a nearby location where the steady source
4. Significance and Use
is not dominant. Though “background noise” by definition
4.1 Evaluation of Environmental Noise—Environmental
includes instrument self-noise, the terms “background sound”
and “background noise” are often used interchangeably with noise is evaluated by comparing a measurement or prediction
of the noise to one or more criteria. There are many different
“residual sound” when it is known that instrument self-noise is
not an issue. criteria and ways of measuring and specifying noise, depend-
ing on the purpose of the evaluation. Some evaluations are
3.2.7 sound exposure level, *SEL, L —where * is a letter
*E
limited to determining compliance with existing regulations or
that denotes the frequency weighting (understood to be A if
ordinances. Others are done in the absence of such require-
deleted), (dB), n—the sound energy over a stated period or
ments or to supplement regulatory evaluations where the
event expressed as the sound level of the equivalent energy
regulations do not address fully or at all the issues of concern.
over a period of 1 s.
3.2.7.1 Discussion—The SEL can be computed as the time- 4.2 Selection of Criteria—This guide provides information
average level of the sound over the event or stated period plus
useful in selecting the appropriate criteria and measurement
10 times the base 10 logarithm of the event duration or stated method to evaluate noise. In making the selection, the user
period in seconds.
should consider the following: regulatory or legal requirements
for the use of a specific criterion; purpose of the evaluation
3.2.8 speech interference level, SIL, L , (dB), n—one-fourth
SI
(regulatory compliance, compatibility, activity interference,
of the sum of the band sound pressure levels for octave bands
aesthetics, comfort, annoyance, health effects, hearing damage,
with nominal mid-band frequencies of 500, 1000, 2000, and
etc.); types of data that are available or could be available
4000 Hz.
(A-weighted, octave band, average level, maximum level,
3.2.9 steady sound, n—sound with negligible variations in
day-night level, calibrated recordings including .wav files from
level over the period of observation.
which various measurements could be made, etc.); and avail-
3.2.10 time above (s or min per h or day), n—the duration
able budget for instrumentation and manpower to obtain that
that the sound level or time-average sound level exceeds a
data. After selecting a measurement method, the user should
corresponding specified level during a specified total measure-
consult appropriate references for more detailed guidance (1).
ment period.
4.3 Objective versus Subjective Evaluations—This guide
3.2.10.1 Discussion—If sound level is used, then the time
discusses objective sound criteria based on measurements and
weighting shall be specified; if time-average sound level is
used, then the measurement time interval for each sample shall
The boldface numbers in parentheses refer to the list of references at the end of
be specified. The frequency weighting should be specified; this standard.
E1686 − 23
regulations based on such. Some local noise ordinances are to sleep. Poor sleep can affect physical ailments and contribute
based solely or partially on subjective judgements of noise. to the potential for degrading task performance that could
Enforcement of these can be easily challenged and, in some result in injuries from accidents when driving or operating
jurisdictions, they are not permitted. These are not further machinery (7).
considered in this guide. One way to address such situations is
5.1.4 Annoyance and Community Reaction—Annoyance is
to evaluate the sound based on reasonable objective criteria.
the effect of a personal reaction to noise. Community reaction
is the response to noise evidenced by complaints to authorities
4.4 Soundscape Methodology—The overall sound environ-
from multiple people. Some people are annoyed but do not
ment as perceived outdoors is often called a soundscape.
complain. Some people use noise as an excuse to complain
Soundscapes have both objective (quantitative) and subjective
when they are not annoyed directly by a sound. Often annoy-
(qualitative) attributes. A soundscape evaluation methodology
ance and community reaction are related to speech or sleep
is evolving which includes methods and criteria that rely
interference, reduced environmental aesthetics, or the effect of
extensively on qualitative factors, both acoustical and non-
these factors on the utility and value of property. Some of the
acoustical, while including requirements for quantitative sound
criteria developed for noise in residential communities are
measurement. Two basic tenets of quantitative soundscape
based on survey studies of annoyance or on adverse commu-
measurements are that the ambient sound at a location is
nity reaction directed to public officials.
comprised of a combination of specific acoustic events that can
be measured individually and in combinations; and that the
5.1.5 Noise Characteristics—Certain quantitative criteria
sounds should be measured using methods that represent the
can be used to further restrict sounds that have been found to
ways in which they are perceived by people. Development of
be particularly noticeable, intrusive, or to increase perceived
such measurement methods specifically for soundscape studies
annoyance especially if persistent. Often such sounds contain
is a part of ongoing research and is not specifically discussed
strong discrete tones or are otherwise unbalanced in spectral
in this document.
content. Spectral criteria such as octave band limits are used to
specify or evaluate the aesthetic quality of the sound present.
5. Bases of Criteria
Some spectral criteria can be used to evaluate whether a sound
is rumbly or hissy or has a perceptible or prominent tone. Other
5.1 Most criteria for environmental noise are based on the
particularly noticeable sounds include information contained in
prevention of problems for people. Historically the emphasis
speech or music as well as impulsive sounds from gunshots,
for noise evaluation in communities has been on annoyance,
bass music beats, hammering, etc. Such sounds are sometimes
speech and sleep interference, and the effects of these on the
restricted to numerically lower A-weighted sound levels in
usability of property. These effects occur at lower levels than
ordinances and regulations. A major concern with music is
typically required to damage hearing, influence task
often the bass beat because of its pulsating nature even if the
performance, or damage structures. Unless the scope of an
level does not exceed normally acceptable criteria for steady
evaluation is limited, it is important to recognize the many
low-frequency sound. In such cases, C-weighted limits or
different problems that may be caused by noise. For example,
octave band limits in the low frequency bands set at a lower
Ref (2) provides a comprehensive discussion of the effects of
level than normal are sometimes applied specifically to the
noise in the context of aviation noise.
music. However, care must be used that such low limits are not
5.1.1 Health Impacts—Damage to human hearing is the best
inappropriately applied to steady sounds. When sound levels
documented effect of noise on health, with the best-established
vary strongly from an average, such as with aircraft overflights
criteria. Poor sleep or stress caused by annoyance can occur at
or an occasional heavy truck pass by, criteria that identify the
much lower sound levels than required for hearing damage and
variation such as “time above” or statistical counts of the
can aggravate some non-auditory physical conditions. Re-
number of events above specified thresholds or within certain
search has shown some physical reactions of the human body
ranges of maximum levels can be used. Measures attempting to
related to sound exposure. These include cardiovascular effects
evaluate for perceived annoyance may take into consideration
such as elevation of blood pressure, mean respiratory volume,
such factors as loudness, the time of day, and various recog-
intestinal irritation, and endocrine system responses among
nized sound quality characteristics.
others. Pyscho-social effects of noise including agitation,
withdrawal, anxiety, and depression among others have also 5.1.6 Land Use Compatibility—Noise compatibility criteria
been identified in the literature. Communities with high noise
have been developed for land use planning. These are most
levels also can have high levels of other pollutants that could useful in determining whether a certain type of development
cause physical problems. Thus, it is difficult to establish a
can be made compatible with existing noise. As discussed in
direct connection between sound exposure and non-auditory ASA/ANSI S12.9 Part 5, these criteria set maximum long-term
health effects (3, 4, 5, 6).
average sound levels with appropriate adjustments for full and
5.1.2 Speech or Communication Interference—Speech com- marginal compatibility of various usages with normal construc-
munication is essential to the daily activities of most people.
tion plus in some cases a higher level in which the use is
There are criteria for the background sound levels needed to compatible with improved construction. The criteria for resi-
allow such communication.
dential uses assume the community is populated by people of
5.1.3 Sleep Interference—High levels of sound and changes average sensitivity to annoyance regardless of sound level with
in sound level can affect the quality of sleep or awaken no self-selection based on existing levels. The ranges are wide
sleepers. Annoying sounds can interfere with the ability to go enough that noticeable and potentially significant changes in
E1686 − 23
sound level could occur within a given compatibility category 6.3.1 “Slow” is a commonly used time weighting especially
without exceeding the criteria. For these reasons as explained in local ordinances because it provides a slowly changing level
in the standard, these criteria do not predict community indication that is easy to read.
reaction to sudden significant increases in the average sound 6.3.2 “Fast” more closely responds to human perception of
level.
sound variation. It provides a more rapid response to changing
sound levels. Fast response is often used for short duration
5.1.7 Preservation of Natural Quiet—Some locations such
measurements such as motor vehicle drive-by tests.
as large park, wilderness, and rural areas are noted for the
6.3.3 “Impulse” allows a faster rise in indicated level than
limited presence of man-made sounds. The preservation of
such existing conditions is often an objective. Refs (8, 9) the fast weighting but causes a slower decrease in indicated
level than the slow weighting so that one can read the
discuss criteria for national parks and wilderness areas, Ref
(10) discusses rural areas, and ASA/ANSI S12.100 discusses maximum levels. The impulse time weighting is no longer
required in sound level meters. As stated in Annex C of IEC
measurements of residual sound in such areas.
61672-1:2002, various investigations have concluded that it “is
not suitable for rating impulsive sounds with respect to their
6. Basics of Sound Measurement
loudness – nor for determining the ‘impulsiveness’ of a sound.”
6.1 Introduction—A classification of the types of sounds by
Since impulse response has been used in some regulations such
temporal, frequency, and spatial characteristics, as well as
as for gunshot sound, the historical specifications for this time
basic procedures for taking sound pressure level measurements
weighting were included in Annex C of IEC 61672-1:2002 but
at a single point in space based on these different
are not included in the 2013 version.
characteristics, are found in ASA/ANSI S1.13. Various mea-
6.3.4 All of the above time weightings will yield different
surements discussed in Section 8 below are affected by
maximum and minimum levels for typical varying sound levels
capabilities built into the sound level meters used for measure-
but yield the same level for a steady source.
ments. This section discusses these capabilities and standards
6.4 Peak Sound Pressure Level—A peak indicator measures
for instruments.
the true peak level of a very short duration signal. It is not
6.2 Frequency Weightings—Several frequency-weighting
normally used to measure steady sounds or slowly varying
networks (filters) have been internationally standardized.
sounds. A peak detector responds to the absolute positive or
These networks provide a better match between measured
negative instantaneous value of the waveform rather than its
sound pressure and human perception. They adjust the relative
effective or “root mean square” (rms) value. In normal use, a
strength of sounds occurring at different frequencies before the
peak measuring instrument will hold its indication for ease of
level is indicated by the meter. The two used most frequently
reading until reset or will store it in a memory for later
are designated A-weighting and C-weighting.
reference. The measured peak level is dependent on the
6.2.1 A-weighting is the most used. Results are expected to
frequency bandwidth of the microphone and both the fre-
indicate human perception or the effects of sound on humans,
quency bandwidth and the rise time (microseconds/volt) of the
most closely correlating (though not exactly) with perceived
associated electronic instrumentation. A reduced frequency
loudness. A-weighting accounts for the reduced sensitivity of
bandwidth will reduce the effective rise time. Sound level
humans to low-frequency sounds, especially at lower sound
meter standards specify tolerances for accuracy of the
levels. In addition to A-weighted sound levels, the weighting
C-weighted peak level but not the rise time. When Z-weighting
curve can be applied to spectra to evaluate the contribution of
is used, it is important to validate the performance of the
various frequencies to the A-weighted sound level.
instrumentation using, for example, a method given in MIL
6.2.2 C-weighting is sometimes used to evaluate sounds
STD 1474E section 4.7.4.3. Some criteria for gunshot sound
containing strong low-frequency components. A large differ-
are based on Z-weighted peak levels. Measuring such at points
ence between C and A weighted levels identifies the presence
far from the source can be difficult because even low-speed
of strong low-frequency sound. It was originally devised to
wind blowing over a microphone can produce a signal below
approximate human perception of high-level sounds.
the frequency range of the gunshot that exceeds the level of the
6.2.3 B, D, and E weightings have been defined but are not
gunshot. C-weighting can function like a high-pass filter
in current instrument standards. The Z-weighting defines the
eliminating the wind effect and allowing the gunshot sound to
frequency limits of the previously non-standardized be measured with little or no wind effect. Rise time can be an
“unweighted,” “linear,” or “flat” weighting.
important factor in some cases such as measurements close to
a firearm. In order to minimize confusion, the term “peak”
6.3 Exponential Time Weightings—Sound levels often vary
should never be used to describe the maximum level measured
rapidly. It is not practical or useful for a meter to indicate every
with fast or slow time weighting since true peak levels can be
fluctuation of sound pressure. When it is desired to record the
more than 20 dB greater than maximum time-weighted levels.
continuous variation in sound, the meter performs an exponen-
tial average process that emphasizes the most recently occur- 6.5 Time-Average Sound Level—(Symbol L*, where * is the
ring sound. Three standard meter time-weighting characteris- measurement period. An additional subscript may indicate the
tics are commonly used in sound measurements (slow, fast, and frequency weighting. The name equivalent sound level, Sym-
impulse). The exponential time weighting used in a measure- bol L , and abbreviation LEQ are also commonly used.)
eq
ment should always be stated. These are sometimes referred to Sometimes it is desirable to measure the average sound present
as a “response” such as “slow response.” over a specified period. This time-average sound level is often
E1686 − 23
called the equivalent sound level or equivalent continuous 7. Adjustments to Sound Levels to Account for
sound level. It is the steady sound level whose sound energy is Conditions Influencing Human Response
equivalent to that of varying sound in the measured period. The
7.1 Introduction—Many acoustical and non-acoustical fac-
frequency weighting should be specified. Otherwise, for over-
tors influence human response to environmental noise. Special
all sound levels, it is understood to be A-weighting.
measurements and criteria apply adjustments to the sound level
for these factors.
6.6 Frequency Analysis—Electronic filters can be used to
separate sound into frequency bands so measurements with any 7.2 Time-of-Day Penalties—Many people expect and need
of the methods described above can be made in specific
lower sound levels at night, primarily for sleep and relaxation.
frequency bands. When frequency analysis is performed for In most outdoor locations, ambient noise levels are lower at
environmental noise, measurements are usually made in stan-
night. It is preferable to have lower limits for sound during
dardized octave or one-third octave bands (IEC 61260-1, normal sleeping hours, most commonly from 10:00 pm until
ASA/ANSI S1.11/Part 1/IEC 61260-1). Octave band or one- 7:00 am. The difference between daytime and nighttime limits
third octave band data or criteria are understood to be Z in local ordinances for residential areas is usually 5 or 10 dB.
weighted unless it is clearly stated otherwise. Frequency For those criteria based on average levels over a period
analysis can be a useful diagnostic tool to characterize, containing both day and night, a 10 dB penalty is commonly
added to sound levels during the night period before computing
identify, and quantify individual sources of sound.
the average level (see 8.5.2). In some cases an evening penalty
6.7 Time History Analysis—Plots of the time history of
of approximately 5 dB is also used (see 8.5.3).
sound variation can demonstrate the variability of sound level
7.3 Penalties based on Sound Characteristics—Sounds that
and serve as a tool in identifying, separating, and quantifying
are concentrated at a specific frequency, or a series of frequen-
individual components of the overall sound that are varying
cies that are typically multiples of the lowest such frequency,
with time. Time history and frequency analysis are sometimes
are called tonal with the individual frequencies being discrete
combined on the same three-dimensional plot. These analyses
tones. Such sounds give the sensation of pitch. These can be
are usually based on calibrated recordings of the sound.
particularly perceptible, intrusive, unpleasant, and annoying,
6.8 Sound Level Meters and Filters—Early sound level
especially if persistent. The same is true of sounds consisting of
meters included the fast and slow time weightings and A and C
repeated pulses less than a second apart, which are called
frequency weightings and no ability to average over longer
repetitive impulsive sounds. In such cases, local noise ordi-
periods. Most newer instruments include the ability to make
nances sometimes specify that the objective criterion be 5 dB
time- average sound level measurements. The sound level
more stringent than would be the case if the sound character
meter specification standard does not call for frequency analy-
were not tonal or impulsive.
sis filters. However, such can be built into meters or attached.
7.4 Normalization or Adjustments to Sound Levels—Some
Other features such as percentile analysis, and long-term
criteria presume conditions that are not appropriate in all cases.
monitoring with measurements over selected periods are often
When these conditions are not met, the measured level can be
found in modern instruments.
adjusted or normalized for the different conditions before
6.8.1 Sound level meters for field use are designated as
comparing it to the normal criterion. This is done by adding or
either class 1 or class 2, with class 1 being more precise.
subtracting a number of decibels from the measured or
6.8.2 International specifications for sound level meters are
calculated expected level for each factor different from the
provided in IEC 61672-1. This standard is often adopted by
normal assumption. The U.S. Environmental Protection
nations as a national standard, and this was done in the United
Agency (EPA) (11) provided a “normalization” procedure
States in 2014 as ASA/ANSI S1.4/Part 1/IEC 61672-1. This
when it introduced the DNL because it found that such
standard defines both a “time weighting” meter also called a
adjustments provided much better correlation with community
“conventional” meter in ASA/ANSI S1.13 and the modern
reactions. Most of the EPA adjustments were taken from earlier
“integrating-averaging” meter with selectable averaging time.
procedures but with some changes. The EPA adjustments
Prior to 2014, standards for sound level meters in the United
addressed seasonal differences, existing sound in the commu-
States were specified in ASA/ANSI S1.4-1983 for conven-
nity without the noise, prior community experience with the
tional sound level meters and ANSI S1.43 for integrating-
noise or community attitudes, and tonal or impulsive charac-
averaging sound level meters. These standards contained more
teristics. Similarly, ASA/ANSI S12.9 Part 4 provides ways to
stringent tolerances at low frequencies than the current stan-
account for various residual or background sound conditions
dard or earlier IEC standards.
and sound characteristics. The measured or calculated DNL is
6.8.3 International specifications for octave band and frac-
“adjusted” upward by 5 dB for tonal or normal impulsive
tional octave band filters are provided in IEC 61260-1. This sound or sound occurring during daytime on weekends, 12 dB
standard is often adopted as a national standard. In the United
for highly impulsive sound such as small arms gunfire,
States this is ASA/ANSI S1.11/Part 1/IEC 61260-1. hammering, riveting, and railyard shunting operations, up to 5
E1686 − 23
dB for normal aircraft sound, and up to 11 dB for rapid onset and time weighting.)—Some criteria (commonly used in local
such as from fast, lowflying aircraft. More complex adjust- ordinances) state maximum sound levels not to be exceeded by
ments are made for strong low-frequency content and high-
time varying sounds when measured with a specified time
energy impulsive sounds. The result is called the “adjusted weighting, fast or slow. This type of criterion with appropriate
DNL.” In an Annex, this standard suggests that in evaluating
limits higher than those for continuous sound is useful when
expected annoyance, appropriate adjustments are up to 5 dB
sound above the specified level creates a problem for even a
for new sounds and up to 10 dB in quiet rural areas, with the
short time, especially if it is recurring. Maximum sound level
two adjustments being additive. Of all these normalization or
limits at an appropriate higher level for such brief sounds are
adjustment factors, only the rapid onset adjustment has been
often used in combination with other criteria at a lower level
incorporated in US federal regulations. The discrete tone or
for continuous sound. Maximum sound level limits alone are
impulsive adjustment is sometimes found in local noise ordi-
insufficient for specifying community noise criteria as they
nances.
cannot appropriately control both brief sounds and continuous
sounds. Sometimes only maximum level limits are stated at
7.5 Psycho-acoustical factors—From a psycho-acoustical
levels more appropriate for an average level and inappropriate
perspective, human response to sound can be positive (for
for occasional brief duration sounds. This results from criteria
example, pleasantness) or negative (for example, annoyance).
originally based on the maximum for a “sound level” that was
Various psycho-acoustical quantities have been developed for
an eyeball average reading of a fluctuating meter needle. In
characterizing separate sensations of sound. These are used in
the methodology called “sound quality” to evaluate and im- modern usage, “maximum level” instead refers to the highest
sound level observed over a period, which could be signifi-
prove the sound of products. Only loudness (see 8.11) and
sharpness (DIN 45692) have been defined in standards. Meth- cantly higher than the average over the period.
ods have been proposed that combine some of these quantities
8.4 Peak Sound Pressure Level (Symbol L . An additional
Pk
to evaluate for negative human response such as annoyance.
subscript may be used to denote frequency weighting.)—When
However, as with the quantities themselves, these methods
sounds are identified as discrete events lasting much less than
have not yet been incorporated into standards (12).
1 s, such as individual gunshots, or hammer blows, it is
8. Sound Measurements, Their Best Uses and appropriate to use the peak level. Further guidance can be
Weaknesses
found in ASA/ANSI S12.7. Peak levels involve no averaging
and are much higher than the maximum levels measured with
8.1 Introduction—There are many ways of measuring and
fast or slow time weighting so that appropriate peak criteria
specifying limits on sound. Sometimes a measurement method
must be applied.
and criterion are specified in a regulation that must be used to
determine regulatory compliance. If an evaluation is for other
8.5 Time-Average Sound Level and Variants—The availabil-
purposes, the most appropriate measurement method and
ity of instruments to measure the time-average sound level has
criteria should be selected for the specific situation. Sometimes
made this a popular way to measure and specify criteria for non
multiple methods could be needed. For a given measurement
steady sounds especially when they vary over only a few dB.
method, the appropriate criterion could be an absolute level or
High-level short-duration events strongly influence the time-
a change in level. For instance, speech interference occurs
average level so it imposes some limit on such. However, there
above some absolute level. However, a criterion based on
is some psychoacoustics uncertainty whether two sounds of the
change in level, possibly also considering changes in other
same energy equivalent level are always perceived by people to
characteristics, may better reflect the impact of a new sound on
be equally loud or annoying. The perceived loudness of a series
a community. This section describes several measurement
of events over a period may be different from the perceived
methods on which criteria are based and discusses their
loudness of a steady sound of the same energy equivalent
strengths and weaknesses. Other factors in the selection of the
average sound level over the same period. Also, in that
best measurement method and criteria are discussed in Section
circumstance the steady sound might not be a problem indoors
9. Further guidance on the use of the most common measures
while the loud events would be clearly heard indoors. The
of overall sound in the outdoor environment, as discussed in
time-average sound level has been used to characterize the
8.2–8.7, can be found in the ASA/ANSI S12.9 series of
long-term acoustical environment. However, people expect and
standards.
need quieter sound levels during some parts of the day.
8.2 Level of Steady Sound—When sound is steady, and its
Therefore, it is common practice to use lower limits at night
frequency content is stable the sound level can be measured
with short-duration time-average levels, or night-time or eve-
with simple instrumentation without the need for averaging or
ning penalties to compute modified long-duration time-average
statistical sampling unless required by a regulation. Criteria
sound levels. The most familiar of these long-duration metrics
may simply state that the sound must not exceed some level,
is the day-night average sound level (DNL). An advantage of
usually A-weighted. If the frequency content is critical to the
the time-average sound level concept is that the expected levels
function and acceptance of the sound, or a possibility that the
can be calculated from databases for common sound sources
sound may not actually be steady, more complex criteria and
without measuring every situation. The frequency weighting
measurements are necessary.
should be specified for all variants of time-average sound level.
8.3 Maximum Sound Level of Time Varying Sound (Symbol Otherwise, A-weighting is understood. Further guidance can be
L . Additional subscripts may be used to denote frequency found in ASA/ANSI S12.9 Part I.
max
E1686 − 23
8.5.1 Time-Average Sound Level—This is the actual energy- average sound level of the event to an energy-equivalent level
equivalent average sound level measured over a specified for a sound lasting exactly 1 s. This is the sound exposure level.
length of time. The time can be anywhere from less than 1 s to For sounds lasting more than 1 s, the sound exposure level will
several years. The time-average sound level measured over a always be greater than both the average and maximum levels of
period from a few minutes to 1 h is often used in local noise the sound. The way in which the event duration is defined may
ordinances. In such cases, it is common to specify a lower be either a specific time, the time during which the sound is
required level at night in residential areas. The time-average within 10 dB of the maximum level, the time the sound is
sound level is one method used by the U.S. Federal Highway above a specified level, or the time the sound is above the
Administration (FHWA) for evaluating highway noise. Time- average residual or background sound level. The most common
average sound level has a clear advantage over a maximum use of sound exposure level is in databases for transportation
level specification since most environmental sounds vary with noise events, from which DNL may be computed. The SEL is
time. A disadvantage is that a single number time-average sometimes used instead of maximum level to describe events.
sound level may disguise a wide variation in sound levels and The disadvantage of this is that people do not easily understand
may not relate to perceptions since it is an energy average SEL.
rather than loudness average.
8.6 Percentile Level (Abbreviation L* and Symbol L ,
*
8.5.2 Day-Night Average Sound Level (Abbreviation DNL,
where * = a number, usually an integer from 1 to 99 indicating
with LDN commonly used, and Symbol L . An additional
dn
the percentage of time the level i
...