Standards Development

Scope

General

This International Standard specifies methods for determining the sound power level of a noise source from sound pressure levels measured on a surface enveloping the noise source (machinery or equipment) in an environment that approximates to an acoustic free field near one or more reflecting planes. The sound power level produced by the noise source, in frequency bands or with A-weighting applied, is calculated using those measurements.

NOTE Differently shaped measurement surfaces can yield differing estimates of the sound power level of a given noise source which are accounted for in the uncertainty associated with this test method, or a test code that refers to this method. An appropriately drafted noise test code (see ISO 12001) gives detailed information on the selection of the surface.

Types of noise and noise sources

The methods specified in this International Standard are suitable for all types of noise (steady, nonsteady, and fluctuating) as defined in ISO 12001, except for short duration, impulsive events. This International Standard is applicable to all types and sizes of noise source (e.g. stationary or slowly moving component or sub-assembly), provided the conditions for the measurements can be met. NOTE It is possible that the conditions for measurements given in this International Standard are impracticable for very tall or very long sources such as chimneys, ducts, conveyors and multi-source industrial plants. A noise test code for the determination of noise emission of specific sources can provide alternative methods in such cases.

Test environment

The test environments that are applicable for measurements made in accordance with this International Standard can be located indoors or outdoors, with one or more sound-reflecting planes present on or near which the noise source under test is mounted. The ideal environment is a completely open space with no bounding or reflecting surfaces other than the reflecting plane(s) (such as that provided by a qualified hemi-anechoic chamber), but procedures are given for applying corrections (within limits that are specified) in the case of environments that are less than ideal. Annex A or ISO 26101 Part 2* defines methods for determining the adequacy of the test environment and for determination of corrections to be applied to account for the effect of the test environment.

Measurement uncertainty

Information is given on the uncertainty of the sound power levels determined in accordance with this International Standard, for measurements made in limited bands of frequency and with frequency Aweighting applied. Annex I outlines procedures for testing laboratories that may be used to reduce measurement uncertainty. The uncertainty conforms to ISO 12001:1996, accuracy grade 2 (engineering grade). General information on measurement uncertainty is provided in this standard and additional information can be found in ISO 5114-1*.

*- Two standardization project NWIPs within ISO/TC 43/SC 1 are circulated for voting parallel to this recommend revision: ISO 26101-2 "Acoustics – Test methods for the qualification of the acoustic environment – Part 2: Determination of the environmental correction" and ISO 5114-1 "Acoustics — Determination of uncertainties associated with sound emission measures – Part 1: sound power levels determined from sound pressure measurements". 

Purpose

ISO 3744 is an important standard used by manufacturers and test laboratories to determine sound power levels of machinery and equipment. ISO 3744 is referenced by hundreds of ISO machinery specific test codes (Type C standards) to determine product sound power levels. Complaints from industrial users of ISO 3744 are that it is too complex and complicated standard and difficult to follow for a large majority of users. Consequently, the experts of ISO/TC 43/SC 1/WG 28 started a committee project to simplify ISO 3744 to make it easier to use and less complex. This revision of ISO 3744 removes items that are seldom used and places other items in two new standards.

For this proposal and its attached document in Annex A the ISO/TC 43/SC 1/WG 28 "Basic machinery noise emission standards" considered the feedback from its expert members on several internal preliminary working drafts. This included also the discussion of the development of the proposed ISO 26101-2 "Acoustics – Test methods for the qualification of the acoustic environment – Part 2: Determination of the environmental correction" and of the proposed ISO 5114-1 "Acoustics — Determination of uncertainties associated with sound emission measures – Part 1: sound power levels determined from sound pressure measurements". WG 28 recommends the parallel development of these three standardization projects to address comprehensive issues.