ISO 3745:2012 pdf download – Acoustics – Determination of sound power levels and sound energy levels of noise sources using sound pressure – Precision methods for anechoic rooms and hemi-anechoic rooms
1.1 General
This International Standard specifes methods for measuring the sound pressure levels on a measurement surface enveloping a noise source (machinery or equipment) in an anechoic room or a hemi-anechoic room. The sound power level (or, in the case of impulsive or transient noise emission, the sound energy level) produced by the noise source, in frequency bands of width one-third octave or with frequency weighting A applied, is calculated using those measurements, including corrections to allow for any differences between the meteorological conditions at the time and place of the test and those corresponding to a reference characteristic acoustic impedance. In general, the frequency range of interest includes the one-third-octave bands with mid-band frequencies from 100 Hz to 10 000 Hz. In practice, the range is extended or restricted to frequencies beyond or within these limits, to those between which the test room is qualifed for the purposes of the measurements.
1.2 Types of noise and noise sources
The methods specifed in this International Standard are suitable for all types of noise (steady, non-steady, fuctuating, isolated bursts of sound energy, etc.) defned in ISO 12001. The noise source under test can be a device, machine, component or sub-assembly. The maximum size of the noise source depends on specifed requirements regarding the radius of the hypothetical sphere or hemisphere used as the enveloping measurement surface.
1.3 Test room
The test rooms that are applicable for measurements made in accordance with this International Standard are an anechoic room or hemi-anechoic room, also called, respectively, a free-feld test room or hemi-free-feld test room.
1.4 Measurement uncertainty
Information is given on the uncertainty of the sound power levels and sound energy levels determined in accordance with this International Standard, for measurements made in limited bands of frequency and with frequency weighting A applied. The uncertainty conforms to ISO 12001:1996, accuracy grade 1 (precision grade).
6.2.2 Verifcation
For instruments used for monitoring meteorological conditions, e.g. to ensure that any of these parameters is within a specifed interval, manufacturer’s specifcations are deemed suffcient to verify these requirements. If any of the meteorological parameters has a direct infuence on the measurement result, the compliance of the measuring instrument with the relevant requirement has to be verifed by a valid calibration certifcate from a laboratory being accredited or otherwise nationally authorized to perform the relevant calibration and ensuring metrological traceability to the appropriate measurement standards.
7.1 General
The manner in which the noise source under test is installed and operated may have a signifcant infuence on the sound power or sound energy emitted by a noise source. This clause specifes conditions that are intended to minimize variations in the noise emission due to the installation and operating conditions of the noise source under test. Relevant instructions of a noise test code, if any exists for the family of machinery or equipment to which the noise source under test belongs, shall be followed. The same installation, mounting and operating conditions of the noise source under test shall be used for the determination of emission sound pressure levels and sound power levels. Particularly for large machines, it is necessary to decide which components, sub-assemblies, auxiliary equipment, power sources; etc., belong to the noise source under test.