AS 3756-1990

1 - AS 3756-1990 ACOUSTICS-MEASUREMENT OF HIGH-FREQUENCY NOISE EMITTED BY COMPUTER AND BUSINESS EQUIPMENT
4 - PREFACE
5 - CONTENTS
6 - 0 Introduction
6 - 1 Scope and field of application
6 - 2 References
6 - 3 Requirements for measurements in a reverberation room
6 - 3.1 General
6 - 3.2 Instrumentation
7 - 3.3 Installation and orientation of microphone
7 - 3.4 Installation and orientation of equipment
7 - 3.5 Calibration of measurement system
7 - 3.6 Measurement of sound pressure level
8 - 4 Method using measured reverberation time
8 - 4.1 General
8 - 4.2 Measurement of reverberation time
8 - 4.3 Calculation of room absorption
8 - 4.4 Installation of microphone and equipment
8 - 4.5 Measurement of sound pressure level
8 - 4.6 Calculation of sound power level
9 - 5 Method using cal culated air absorption
9 - 5.1 General
9 - 5.2 Calculation of room constant
9 - 5.3 Temperature and humidity conditions during measurements
9 - 5.4 Installation of microphone and equipment
9 - 5.5 Measurement of sound pressure level
10 - 5.6 Calculation of sound power level
10 - 6 Method using a reference sound source
10 - 6.1 Reference sound source
10 - 6.2 Installation of microphone and equipment
10 - 6.3 Installation of reference sound source
11 - 6.4 Measurement of sound pressure level
11 - 6.5 Calculation of sound power level
11 - 6.5.1 Equipment emitting broad-band noise
11 - 6.5.2 Equipment emitting discrete frequency tone(s)
11 - 7 Method using a free field over a reflecting plane
11 - 7.1 General
11 - 7.2 Instrumentation
11 - 7.3 Installation and orientation of microphone
12 - 7.4 Installation of equipment
12 - 7.5 Calibration of measurement system
12 - 7.6 Measurement of sound pressure level
12 - 7.7 Calculation of surface sound pressure level
12 - 7.8 Calculation of sound power level
12 - 8 Calculation of A-weighted sound power level
13 - 9 Information to be recorded
13 - 9.1 Equipment under test
13 - 9.2 Acoustic environment
13 - 9.3 Instrumentation
13 - 9.4 Acoustical data
14 - 10 Information to be reported
15 - Annex A - Coaxial circular paths in parallel planes for microphone traverses in a free field over a reflecting plane
16 - Annex B - Calculation of air absorption coefficient

Specifies four methods for the determination of the sound power levels of high-frequency noise emitted by computer and business equipment in the frequency range covered by the octave band centred at 16 kHz. Identical with and reproduced from ISO 9295.

This International Standard specifies four methods for the determination of the sound power levels of high- frequency noise emitted by computer and business equipment in the frequency range covered by the octave band centred at 16 kHz. They are complementary to the methods described in ISO 7779. The first three methods are based on the reverberation room technique described in clause 5 of ISO 7779 : 1988. The fourth method makes use of a free field over a reflecting plane as described in clause 6 of ISO 7779 : 1988.The test conditions which prescribe the installation and operation of the equipment are those specified in ISO 7779.While the four methods described in this International Standard are particularly suitable for computer and business equipment, they may also be applied to other types of equipment. This International Standard specifies methods for the determination of sound power levels in the frequency range covered by the octave band centred at 16 kHz which includes frequencies between 11,2 kHz and 22,4 kHz.NOTE - The sound power level in the 16 kHz octave band determined according to this International Standard typically is subject to a standard deviation of approximately 3 dB.A method for the measurement of high-frequency noise is in conformance with this International Standard if it satisfies all the mandatory requirements of one of the four methods described herein and if the information recorded and reported is that specified in clauses 8, 9 and 10, respectively.