AS 3755-1990

Acoustics - Measurement of airborne noise emitted by computer and business equipment

Standards Australia

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1 - AS 3755-1990 ACOUSTICS-MEASUREMENT OF AIRBORNE NOISE EMITTED BY COMPUTER AND BUSINESS EQUIPMENT
4 - PREFACE
5 - CONTENTS
6 - 0 Introduction
6 - 1 Scope and field of application
6 - 1.1 Scope
6 - 1.2 Field of application
7 - 2 Conformance
7 - 3 References
7 - 4 Definitions
7 - 4.1 level of background noise:
7 - 4.2 bystander:
7 - 4.3 bystander position:
7 - 4.4 computerand business equipment:
7 - 4.5 floor-standing equipment:
7 - 4.6 frequency range of interest:
7 - 4.7 functional unit:
7 - 4.8 idling mode:
7 - 4.9 measurement surface:
7 - 4.10 operating mode:
7 - 4.11 operator:
8 - 4.12 operator position:
8 - 4.13 rack-mounted equipment:
8 - 4.14 reference box:
8 - 4.15 reference sound source:
8 - 4.16 sound power level,
8 - 4.17 sound pressure level,
8 - 4.18 standard test table:
8 - 4.19 sub-assembly:
8 - 4.20 surface-average sound pressure level
8 - 4.21 table-top equipment:
8 - 4.22 time-average sound pressure level
8 - 4.23 wall-mounted equipment:
8 - 5 Method for determining sound power levels of equipment in reverberation rooms
8 - 5.1 General
8 - 5.2 Measurement uncertainty
8 - 5.3 Test environment
8 - 5.3.1 General
9 - 5.3.2 Test room volume
9 - 5.3.3 Level of background noise
9 - 5.3.4 Temperature and relative humidity
9 - 5.4 Instrumentation
9 - 5.4.1 General
9 - 5.4.2 Microphone and its associated cable
9 - 5.4.3 Frequency response of the instrumentation system
9 - 5.4.4 Reference sound source
9 - 5.4.5 Filter characteristics
9 - 5.4.6 Calibration
10 - 5.5 Installation and operation of equipment - General requirements
10 - 5.5.1 Equipment installation
10 - 5.5.2 Input voltage and frequency
10 - 5.5.3 Equipment operation
11 - 5.6 Microphone and source positions
11 - 5.6.1 Identification of discrete-frequency components and narrow bands of noise
11 - 5.6.2 Number of microphone positions
12 - 5.6.3 Microphone arrangement 5.6.4 Number of equipment locations
12 - 5.7 Measurement of sound pressure levels
12 - 5.7.1 General
13 - 5.7.2 Measurement duration
13 - 5.7.3 Corrections for background noise
13 - 5.8 Measurement of the sound pressure level of the reference sound source
13 - 5.9 Calculation of space/time-average band sound pressure levels
14 - 5.10 Calculation of sound power levels
14 - 5.10.1 Calculation of band sound power levels
14 - 5.10.2 Calculation of A-weighted sound power level
14 - 5.11 Information to be recorded
14 - 5.11.1 Equipment being tested
15 - 5.11.2 Acoustical environment
15 - 5.11.3 Instrumentation
15 - 5.11.4 Acoustical data
15 - 5.12 Test report
15 - 6 Method for determining sound power levels of equipment under essentially free-field conditions over a reflecting plane
15 - 6.1 General
15 - 6.2 Measurement uncertainty
16 - 6.3 Test environment
16 - 6.3.1 General
16 - 6.3.2 Adequacy of the test environment
16 - 6.3.3 Level of background noise
16 - 6.3.4 Temperature and relative humidity
16 - 6.4 Instrumentation
16 - 6.4.1 General
16 - 6.4.2 Microphone and its associated cable
16 - 6.4.3 Frequency response of the instrumentation system
17 - 6.4.4 Weighting network and filter characteristics
17 - 6.4.5 Calibration
17 - 6.5 Installation and operation of equipment-General requirements
17 - 6.5.1 Equipment installation
17 - 6.5.2 Input voltage and frequency
17 - 6.5.3 Equipment operation
18 - 6.6 Measurement surface and microphone positions
18 - 6.6.1 General
19 - 6.6.2 Microphone positions on the measurement surface
21 - 6.6.3 Additional microphone positions on the measurement surface
21 - 6.6.4 Reduction in the number of microphone positions
21 - 6.7 Measurement of sound pressure levels
21 - 6.7.1 General
21 - 6.7.2 Measurement duration
21 - 6.7.3 Corrections for background noise
22 - 6.8 Corrections for unwanted reflections
22 - 6.9 Calculation of surface-average sound pressure level
22 - 6.9.1 Calculation of sound pressure level averaged over the measurement surface
22 - 6.9.2 Calculation of surface-average sound pressure level
22 - 6.10 Calculation of sound power level
23 - 6.11 Information to be recorded
23 - 6.11.1 Equipment being tested
23 - 6.11.2 Acoustical environment
23 - 6.11.3 Instrumentation
23 - 6.11.4 Acoustical data
23 - 6.12 Test report
24 - 7 Method for measuring sound pressure levels at the operator and bystander positions
24 - 7.1 General
24 - 7.2 Measurement uncertainty
24 - 7.3 Test environment
24 - 7.3.1 General
24 - 7.3.2 Adequacy of the test environment
24 - 7.3.3 Level of background noise
24 - 7.3.4 Temperature and relative humidity
24 - 7.4 Instrumentation
24 - 7.5 Installation and operation of equipment
24 - 7.6 Microphone positions
24 - 7.6.1 At the operator position(s)
25 - 7.6.2 At the bystander position(s)
25 - 7.6.3 Microphone orientation
26 - 7.7 Measurement of sound pressure levels
26 - 7.7.1 General
26 - 7.7.2 Measurement duration
26 - 7.7.3 Corrections for background noise
26 - 7.7.4 Corrections for unwanted reflections
26 - 7.8 Calculation of the mean sound pressure level at the bystander position
26 - 7.9 Information to be recorded
26 - 7.9.1 Equipment being tested
26 - 7.9.2 Acoustical environment
26 - 7.9.3 Instrumentation
27 - 7.9.4 Acoustical data
27 - 7.10 Test report
28 - Annex A - Standard test table
29 - Annex B - Alternative measurement surfaces for sound power measurements in accordance with clause 6
29 - B.1 Arrangement 3: Hemispherical measurement surface - 10 measurement positions
29 - B.2 Arrangement 4: Hemispherical measurement surface - 10 measurement positions
30 - B.3 Arrangement 5: Coaxial circular paths in parallel planes for microphone traverses in a free field over a reflecting plane
30 - B.4 Arrangement 6: Quarter-sphere measurement surface - 5 measurement positions
31 - Annex C - Installation and operating conditions for specific equipment categories
31 - C.1 General
31 - C.2 Equipment category: Typewriters
32 - C.3 Equipment category: Printers
33 - C.4 Equipment category: Teleprinters
36 - C.5 Equipment category: Keyboards
36 - C.6 Equipment category: Duplicators
37 - C.7 Equipment category: Card readers and card punches
38 - C.8 Equipment category: Magnetic tape storage units
38 - C.9 Equipment category: Magnetic disk storage units
39 - C.10 Equipment category: Visual display units
39 - C.11 Equipment category: Electronic units
39 - C.12 Equipment category: Microform readers
40 - Annex D - Measurement of impulsive sound pressure levels and discrete tones at the operator position
40 - D.1 Scope
40 - D.2 Microphone position
40 - D.3 Measurement of impulsive sound
40 - D.4 Detection of prominent discrete tones
42 - D.5 Information to be reported
42 - D.6 Bibliography

Abstract

Specifies procedures for measuring and reporting the noise emitted by computer and business equipment. The basic emission quantity is the A-weighted sound power level which may be used for comparing equipment of the same type, but from different manufacturers, or for comparing different equipment. Two methods for determining the sound power levels are specified in order to avoid undue restriction on existing facilities and experience. Identical with and reproduced from ISO 7779.

Scope

This International Standard specifies procedures for measuring and reporting the noise emitted by computer and business equipment. It is based on the measurement procedures specified in ISO 3740, ISO 3741, ISO 3742,
ISO 3744 and ISO 3745. The basic emission quantity is the A-weighted sound power level which may be used for comparing equipment of the same type, but from different manufacturers, or for comparing different equipment.
The A-weighted sound power level is supplemented by the A-weighted sound pressure level measuredat the operator position(s) or the bystander positions. This sound pressure level is not a measurement of total occupational noise exposure of workers (noise immission).
Two methods for determining the sound power levels are specified in this International Standard in order to avoid undue restriction on existing facilities and experience. The first method is based on reverberant room measurements (see ISO 3741 and ISO 3742); the second is based on measurements in an essentially free field over a reflecting plane (see ISO 3744 and ISO 3745). Either method may be used in accordance with this International Standard. They are comparable in accuracy and yield the same A-weighted sound power level within the tolerance range of the methods specified in this International Standard.
Field of application
This International Standard is suitable for type tests and provides methods for manufacturers and testing laboratories to obtain comparable results.
The method specified in clause 5 provides a comparison procedure for determining sound power levels in a reverberation room. The method specified in clause 6 provides a direct procedure for determining sound power levels using essentially free-field conditions over a reflecting plane. The method specified in clause 7 provides a procedure for measuring noise at the operator or bystander positions. The proceduresin this International Standard may be applied to equipment which radiates broad-band noise, narrow-band noise, noise which contains discrete-frequency components or impulsive noise.
The methods specified in this International Standard allow the determination of noise emission levels for a unit tested individually.
The sound power levels and sound pressure levels are used for noise emission declaration and comparison purposes. They are not to be considered as installation noise levels, however they may be used for installation planning.
If sound power levels obtained are determined for several units of the same production series, the result can be used to determine a statistical value for that production series.