1 Scope
1.1 General
This standard specifies measurements on silencers in situ. It is applicable to measurements on silencers in practical applications for acoustic analysis, acceptance tests and evaluations. Results obtained in accordance with this standard cannot be compared to performance data obtained from laboratory measurements on ducted silencers in accordance with ISO 7235 or GB/T 4760, partly because of different test conditions (such as sound field distribution, flow, temperature and installation conditions) and partly because of different definitions.
Depending on the measurement methods, the measurement results may be classified as:
insertion loss Dis
or transmission loss Dts
Note: “s” stands for "in situ”, “i” for insertion and “t” for transmission.
The measurement method depends upon the type of silencer and the installation conditions (e.g. insertion loss measurements must be carried out for blowdown silencers). Additional characteristic quantities, which could include measurements taken using artificial sound sources or measurements taken to determine the directivity of sound propagation from the silencer, maybe agreed upon in accordance with this standard.
1.2 Application Scope of This Standard
a) Silencers which are installed either as a whole or in the form of individual baffles in the propagation path of sound (e.g. openings of ducts) originating from a sound source (machine, plant, building, plant such as a gas turbine generator, scrubbing plant, cooling tower, heating ventilation and air conditioning (HVAC) plant, exhaust stack, air intake duct, weapon, internal combustion engine, compressor, etc.);
b) All types of passive silencers (absorptive, reactive, reflection and blowdown silencer);
c) Active silencers (involving amplifiers and loudspeakers) as far as the insertion loss of passive silencers is equivalent to the off/on conditions of active devices;
d) Other measures or means of effecting acoustic attenuation in air or other gases (e.g. components installed in ducting, louvres, grilles and deflector hoods).
e) This standard is applicable to the determination of the effect of cleaning or refurbishing silencers
This standard is not applicable to closed high-pressure systems (e.g. silencers in closed ducts) since measurements of structure-borne sound are not anticipated.
1.3 Quantities to be Measured
a) Sound pressure level
Foreword i
Introduction ii
1 Scope
1.1 General
1.2 Application Scope of This Standard
1.3 Quantities to be Measured
2 Normative References
3 Terms and Definitions
4 Corrections for Background Noise
4.1 Transmission Sound Pressure Level Difference
4.2 Insertion Sound Pressure Level Difference
5 Installation Conditions
6 Measuring Instruments
6.1 Acoustic Instruments
6.2 Air Flow, Static Pressure and Temperature Measuring Devices
7 Test Object and Measuring Conditions
8 Measurement Procedures
8.1 General
8.2 Acoustic Measurements
8.3 Flow, Pressure and Temperature Measurements
9 Evaluation
9.1 Evaluation of Sound Pressure Measurements
9.2 Evaluation of Flow Measurements
10 Information to be Recorded
10.1 Description of the Tested Silencer:
10.2 Description of the Operating Conditions:
10.3 Description of the Test Method:
10.4 Acoustical Test Results:
10.5 Further information:
11 Information to be Reported
Annex A (Informative) Field Corrections
Annex B (Informative) Calibration of Directional Microphones and Microphones Equipped with a Turbulence Windscreen
Annex C (Informative) Bibliography
