In This Issue
Summer Bridge on Noise Control Engineering
June 15, 2021 Volume 51 Issue 2
What is the role of engineering practice, education, and standards in mitigating human-generated noise? The articles in this issue survey these aspects of the US noise landscape, and offer updates and useful resources.

Voluntary National and International Noise Standards for Products and Machines

Tuesday, June 15, 2021

Author: Robert D. Hellweg Jr.

Regularly updated national and international
noise standards ensure consistency and accuracy
among products.

Voluntary noise standards, which are developed by consensus-based standards organizations, define reliable and reproducible procedures to ensure that manufacturers (i) design their products to meet customer, market, and/or regulatory requirements; (ii) get components that meet their specifications; and (iii) report noise values that are measured in the same way as their competitors so that purchasers can trust values of product noise levels given by manufacturers. The use of these standards can lead to quieter products resulting in better working conditions, quality of life, and worker health as well as competitive advantages.

The importance of measurement standards was summarized by William Thomson, Lord Kelvin (1891, p. 80):

  • “To measure is to know.”
  • “If you cannot measure it, you cannot improve it.”
  • “When you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind.”

Product Noise Metrics

There are two different aspects of product noise: the noise emitted by a product and the noise measured from a product in situ.

The primary descriptor of the noise emitted by a product is the sound power level, supplemented by the emission sound pressure level at an operator position. Both are independent of the environment in which the product is located. These sound levels are important for design purposes and, when using psychoacoustic standards, for evaluating annoying aspects of product sounds (e.g., prominent discrete tones, roughness). The product sound power level can be used to compare the noise of different manufacturers’ products, such as computers, dishwashers, and manufacturing machinery.

Sound levels are important for design purposes
and, when using psychoacoustic standards, for
evaluating annoying aspects of product sounds.

The descriptor of the sound that is produced from a product measured in its installed location is the in situ sound pressure level, which takes into account the effects of where the source is located and sound reflections from walls. The in situ sound pressure level is a descriptor for the sounds heard by persons, whether users, bystanders, or community.

The sound power level is measured in decibels (dB) relative to 1 picowatt and the sound pressure level is measured in dB relative to 20 micropascals. For most products the two sound levels are A-weighted; that is, the sounds are frequency weighted according to the A-weighting curve, which approximates human hearing for midlevel sounds, and reported in dBA.

Standards Organizations

Many US and international organizations develop acoustical and noise standards.

The American National Standards Institute (ANSI) has accredited standards committees (ASCs) on acoustics, bioacoustics, mechanical vibration and shock, and noise, all administered by the Acoustical Society of America (ASA). Founded in 1929, ASA sponsored the development of acoustical standards through its committee on Acoustical Standardization (Blaeser and Struck 2019). And standardization has remained important to ASA, as demonstrated by the fact that six ASA presidents and two vice presidents have been the ­society’s standards leaders or directors (four of the ­leaders were also NAE members).

Other ANSI-accredited standards organizations with acoustical or noise standards include the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE), ASTM International ­(formerly known as the American Society for Testing and ­Materials), American Society of Mechanical Engineers (ASME), Air Conditioning, Heating, and Refrigeration Institute (AHRI), and SAE International (formerly the Society of Automotive Engineers). George Maling (2021) in this issue further discusses various organizations with acoustical or noise standards.

The International Organization for Standardization (ISO) has relevant technical committees (TCs) and subcommittees (SCs), including TC43 (Acoustics) and TC43/SC1 (Noise). Some ISO standards are the basic acoustic standards for the measurement of product and equipment noise.

The International Electrotechnical Commission (IEC) develops standards for acoustical instruments as well as electrical, electronic, and related technologies, including acoustical measurement instruments, household appliances, and wind turbines.

Basic Standards for Measuring Product and Equipment Noise

Basic product acoustic standards include criteria for measuring noise from various types of products and machinery and outline general mounting and operating conditions. Product-specific standards use the basic standards that have the type of measurement and the grade of measurement uncertainty desired. Grades of measurement uncertainty are characterized as precision (class 1), engineering (class 2), and survey (class 3). Product-specific standards also define product mounting and operating conditions and operator position for measuring the emission sound pressure level.

ISO basic sound power level and emission sound pressure level standards were developed beginning in the early 1970s. William W. Lang (NAE), leader of the ISO subgroup and then chair of the working group that developed these standards, recognized the need for effective, reliable, and uniform measurement procedures.

For Measuring Sound Power Levels

There are two sets of ISO basic product standards for the determination of sound power levels:

  • ISO 3741 to 3747 (using sound pressure level measurements) (the US adoptions of these ISO standards are the ANSI/ASA S12.51–S12.57 series)
  • ISO 9614-1 to 9614-3 (using sound intensity measurements) (the US sound intensity standard is ANSI/ASA S12.12).

The procedures in ISO 3744, 3747, and 9614-2 meet engineering-grade accuracy, which is advantageous to manufacturers, and especially for legal requirements; ISO 3741, 3745, and 9614-3 meet precision-grade accuracy.

The ISO 3741–3747 series provides for measurements in reverberant test rooms and fields, anechoic chambers, hemi-anechoic chambers (rooms with anechoic properties above a reflecting plane), essentially free-field over a reflecting plane, and in situ in a reverberant environment. ISO standards also provide criteria for qualifying anechoic and hemi-anechoic chambers.

ISO 3744 (engineering grade) is the most commonly used basic product noise standard in product-specific standards and is referenced in several European Commission regulations and test procedures. It is under revision to simplify the methods and procedures and to remove most of the provisions for determining environmental correction factors, which will go into a separate updated ISO standard

ISO 9295 specifies methods for the determination of sound power levels in the high-frequency range. It could serve as the basis for standards to measure frequencies for products that emit ultrasound, such as some medical devices.

ISO sound intensity standards for determining sound power levels include significant requirements on ­stationary background noise and other factors that make them more difficult to perform reproducibly. But sound intensity measurements are a valuable tool for testing products that are too large for the test spaces in the ISO 3741–3747 series and for locating specific sources of noise in a product, supplemented by knowledge of the product operating conditions.

For Measuring Emission Sound Pressure Levels

The ISO basic product standards for determining emission sound pressure levels (ISO 11201–11205) have different grades of accuracy. Their methods involve using (i) measurements in a free field over a reflective plane with negligible, approximate, or accurate environmental corrections; (ii) calculations from the sound power level; and (iii) sound intensity measurements.

For Declaring Product and Equipment Sound Levels

The ISO basic product acoustic standard for declaring (or publishing) product and equipment sound levels (ISO 4871) calls for either adding uncertainty to the measured values for a “guaranteed” level or reporting the measured value and the uncertainty.

An ISO standard may be used to measure frequencies for products that
emit ultrasound, such as some medical devices.

The newly approved US standard for declaring product sound levels (ANSI/ASA 12.61:2020) uses a different approach to achieve the same results. The mean measured value is always reported, and the uncertainty is optionally reported (e.g., when required by regulatory authorities). If the uncertainty value is not reported, methods of verifying the declared levels are given.

Other Acoustic and Noise Standards Related to Product Noise

An ISO standard (9613-2, attenuation of outdoor sound propagation) predicts the equivalent continuous A-weighted sound pressure level under various meteorological, terrain, vegetation, and barrier conditions. Software programs implement the calculation ­methods of this standard to predict sound pressure levels in communities from sound power levels of sources such as wind turbines, emergency generators, and transformers.

ANSI/ASA S12.2 provides three methods for evaluating room noise: a survey method that employs the in situ A-weighted sound pressure level, an engineering method that uses expanded noise criteria (NC) curves, and a method for evaluating low-frequency fluctuating noise that uses room noise criterion (RNC) curves. An informative annex to this standard gives recommended noise level criteria for various occupied activity areas; for example, the A-weighted sound pressure level criteria for classrooms are the same as the maximum one-hour sound levels in ANSI/ASA S12.60 (Parts 1 and 2) for classroom acoustics. Product manufacturers can use these criteria to determine sound power levels for the activity areas in which the products will be located.

Product-Specific Noise Standards

Information Technology Products

In the 1970s the information technology (IT) industry recognized noise as a factor in both customer ­acceptability and possible government regulations. International IT noise standards were created by industry, government, and users based on standards developed by American and European industry trade associations in cooperation with ASA standards committees. ANSI S1.29-1979 became the basis for the Ecma ­International[1] standard ECMA-74, which was the basis for ISO 7779.

The IT industry recognizes noise as a factor in both customer acceptability and possible government regulations.

ISO 7779 and ECMA-74—both used worldwide and cited in European directives and regulations—include product-specific operating and mounting conditions for A-weighted sound power and sound pressure levels. The US equivalent is ANSI/ASA S12.10/Part 1.

New IT products are introduced regularly, of course, and operating modes may change as products evolve, so it is necessary to frequently revise these standards. Because the revision cycle for ECMA-74 is considerably shorter than for ISO revisions, ISO 7779 now refers to product mounting and operating conditions in the current edition of ECMA-74.

The IT industry also has standards for declared noise levels: ISO 9296 and its more up-to-date counterpart ECMA-109 (10th edition), which has methods similar to ANSI/ASA S12.61.

The IT industry also developed standards for determining air- and structure-borne sound power levels from small fans (ISO 10302-1/ECMA-275-1 and ISO 10302-2/ECMA 275-2, respectively). A fan mounted on a special acoustically “transparent” plenum can operate under pressure loading conditions similar to those when installed in computer systems. The previous noise descriptor for fans—an emission sound pressure level under no load conditions—was not useful for selecting fans used in computer products.

The German Environment Agency Blue Angel[2] is an environmental label (“The German Eco-Label”) for many product types. Its noise criterion is the A-weighted sound power level, and for IT equipment it is measured according to ISO 7779 and reported according to ISO 9296. The Blue Angel sound power level criterion for desktop computers in 2015 was 10–13 dBA lower than in 1995, and there was a similar reduction in measured product sound power levels, reductions that may be attributed to energy efficiencies, source noise control techniques, enclosure designs—and uniform worldwide measurement and declaration standards (Beltman 2016).

Household Appliances

There are numerous product-specific IEC noise standards for household appliances and similar devices (IEC 62704-1, -2, and -3 series). For some, the A-weighted sound power level methods are based on ISO 3744 with product-specific operating and mounting conditions; the declaration standard is based on ISO 4871. The European Commission requires appliances’ energy labels to display the declared A-weighted sound power level determined according to these IEC standards.

Wind Turbines

Large wind turbines emit sound power levels characterized by modulation and “swooshing.” The IEC 61400-11 standard “Wind turbine acoustic noise measurement techniques” specifies methods to determine A-weighted sound power levels. Sound pressure levels are measured at a single microphone location and hemispherical spreading is assumed to determine the sound power ­levels as a function of wind turbine electrical output power.

The IEC wind turbine sound power level values are used as input data for computer programs (based on ISO 9613-2) that predict energy-equivalent sound pressure levels at residential receptors. Experience has shown good agreement between predicted and measured wind turbine energy-equivalent sound pressure levels with the appropriate selection of ground factors and other settings in the programs (Kaliski et al. 2018). In many communities and states the criteria for approval of the installation of wind turbines require predictions of sound pressure levels using programs based on ISO 9613-2.

Other Product Types

The uses and applications of noise measurement standards described suggest opportunities for the use of such standards for other types of products.

Small Unmanned Aircraft Systems: Drones

Small unmanned aircraft systems (UAS) are regulated in the United States by the Federal Aviation Administration. It has been suggested, based on the experience of the IT and wind turbine industries, that the A-weighted sound power level may be suitable to quantify small drone noise emissions (Hellweg and Maling 2020), an approach that has the following advantages:

  • Different measurement methods may be used and can be taken indoors or outdoors.
  • Sound power levels can meet the needs of manufacturers, users, the public, and governments.
  • Community sound pressure levels can be predicted from the sound power levels.

Implementation of this suggestion requires selecting a method to determine sound power levels for various operating modes.

The ASC S12 (Noise) Working Group 58 is developing an ANSI/ASA standard to determine the A-­weighted sound power level of small UAS (less than 25 kg) in an anechoic room and is also considering outdoor measurements.

The European Commission (2019) enacted a delegated regulation on small UAS that requires measuring and publishing A-weighted sound power levels according to ISO 3744. It also sets limits on maximum A-weighted sound power levels for small UAS of 0.25–4 kg.

A joint working group WG7 of ISO TC20/SC16 (Unmanned Aircraft Systems) and ISO TC43/SC1 (Noise) has begun development of a standard for noise measurements of small multirotor UAS.

Hand Dryers

A recent study of hand dryers showed that A-weighted sound pressure levels measured in situ are both very loud and significantly noisier when hands are in the airstream (Keegan 2020a).

A recent study showed that hand dryers are both very loud and significantly noisier when hands are in the airstream.

At least one manufacturer’s laboratory measured noise without the effect of hands in the airstream and did not measure the operator position sound pressure level, only the sound power level (Keegan 2020b). The manufacturer said it could not measure at the operator position because the device was tested on the floor of a hemi-anechoic chamber. ISO standards require that equipment designed to be operated on a wall be installed on a wall for measuring operator position sound pressure levels, since there are reflections from both the wall and the reflecting surface in the test room.

ISO standards also require testing in a mode “representative of the noisiest operation in typical usage,” so the operating mode of hand dryers during acoustic tests should simulate hand interference.

Experience indicates that it is practicable to measure the operator position of wall-mounted IT products on a portable wall in a hemi-anechoic chamber to meet ISO requirements.

Psychoacoustic Standards

Psychoacoustic standards can help manufacturers understand how their products will be perceived by users in order to reduce annoying aspects of product noise during design. Psychoacoustic parameters used to define the perception of noise include loudness, prominent tones and tonality, and roughness.


There are two ISO standards with methods for calculating loudness and a third under development:

•  ISO 532-1: Part 1: Zwicker method

•  ISO 532-2: Part 2: Moore-Glasberg method

•  ISO/AWI 532-3 (under development): Part 3: Moore-Glasberg-Schlittenlacher method for time-varying sounds.

The ANSI/ASA S3.4 loudness standard is similar to ISO 532-2, and includes a software program.

Prominent Tones and Tonality

If a product’s noise has tonal components that are ­several decibels above noticeability and are deemed to be prominent, the noise emissions could be annoying depending on other background sounds. Several product-specific standards have methods for the measurement of prominent discrete tones or tonality.

IT Industry

The IT industry has three methods each using ­narrow-band fast Fourier transform (FFT) analyses: two for prominent discrete tones and one for prominent ­tonality. Some IT developers also use narrow-band data to identify the source of unwanted sounds in their products. Several IT manufacturers have criteria on prominent discrete tones in their purchase specifications for components (e.g., hard disk drives and fans).

Some IT developers use narrow-band data to identify the source of unwanted sounds in their products.

The newest standards on tonality are ECMA-418 psychoacoustic metrics for IT equipment: Part 1 for prominent discrete tones and Part 2 for models based on human perception. ECMA-418-1 replaces and updates technical content with methods to determine the tone-to-noise ratio and the prominence ratio, and ECMA-418-2 provides a prominent tonality method based on a hearing model (Sottek 2016).

Wind Turbines

The IEC 61704-11 standard uses an FFT method to evaluate tonality from sound pressure level measurements to determine sound power levels.


Other procedures evaluate tonal components for general or environmental evaluations of product noise in situ or in laboratories. The ISO/PAS 20065 publicly available specification uses a narrow-band FFT method to determine the audibility and prominence of tones in noise. It is being revised as a technical specification to eventually become an international standard. Its methods are used in ISO 1996-2, “Determination of environmental sound pressure levels,” to determine audibility and prominence of tones in environmental noise.


ECMA 418-2 uses a method based on the hearing model (Sottek 2016) to determine roughness and whether it is prominent.


Noise standards are important in the development of quiet products and are referenced in national and international regulations to ensure uniformity of measurements and to avoid conflicting methods. Used by manufacturers, purchasers, and governments, they are continually assessed and should be updated to respond in a timely and responsible manner to new product types, technologies, and capabilities. Noise control engineers are instrumental in the development and implementation of such standards to reduce harmful noise impacts and enhance quality of life.


Beltman M. 2016. Experience with noise emission declarations and labels: Information technology industry. Buy Quiet ­Symposium, International INCE, Aug 25, ­Hamburg.

Blaeser S, Struck CJ. 2019. A history of ASA standards. ­Journal of the Acoustical Society of America 145(1):77–109.

European Commission. 2019. Delegated Regulation (EU) 2019/945 of 12 March 2019 on unmanned aircraft ­systems and on third-country operators of unmanned aircraft ­systems. Official Journal of the European Union 62(L 152).

Hellweg RD Jr, Maling GC Jr. 2020. Noise regulation: Federal standards or self-certification by the private sector? In: Engineering a Quieter America: UAS and UAV (Drone) Noise Emissions and Noise Control Engineering Technology. Reston VA: INCE-USA.

Kaliski K, Bastasch M, O’Neal R. 2018. Regulating and predicting wind turbine sound in the US. Proceedings, INTER-NOISE 2018, Aug 26–29, Chicago.

Keegan NL. 2020a. Children who say hand dryers “hurt my ears” are correct: A real-world study examining the loudness of automated hand dryers in public places. Paediatrics & Child Health 25(4):216–21.

Keegan N. 2020b. Hair dryer noise: Identifying the problem and proposing a solution. Plenary lecture, NOISE-CON 2020, Nov 16–20 (online).

Maling GC Jr. 2021. Resources for noise control engineering. The Bridge 51(2):41–47.

Sottek R. 2016. A hearing model approach to time-varying loudness. Acta Acustica united with Acustica 102(4):725–44.

Thomson W. 1891. Popular Lectures and Addresses, Vol I. London: MacMillan.


[1]  Formerly the European Computer Manufacturers Association


About the Author:Robert Hellweg is sole proprietor of Hellweg Acoustics and treasurer of the INCE Foundation.