Recommended verification method for calibration conditions in
multi-channel simultaneous acoustical noise measurement system

JBMIA-TR-28 :2014（ 2019re-affirmation ）Disclaimer
This is a translation of the authoritative text which JBMIA published here
http://hyojunka.jbmia.or.jp/hyojun2/upload-v3.2/archive/TR-28.pdf
This translated document is provided for convenience only;
any references to JBMIA on this document must be based on the Japaneseversion.

Established May, 2014

Japan Business Machine and Information System Industries Association
Sub-working group 2 of working group for investigationsof acoustical noise standards and specifications,
Environmental committeeJBMS-TR-28:2014

Sub-working group 2 for improving calibration work of measurement
system of working group for investigations of acoustical noise standards
and specifications, Environmental Committee(Leader)

Kohei Shimoda †Fuji Xerox Co., Ltd.

KONICA MINOLTA, INC.
Shigeru Tashiro
Kouji Tanaka
CANON INC.
Ikuo Kimizuka
IBM Japan, Ltd.
Hiroshi TairaJQA (Japan Quality Assurance Organization)
Masaki Suzuki
Lenovo Japan Ltd.
Yoshitaka Shirota
ONO SOKKI Co., Ltd.
Ricoh Company, Ltd.
Shinichi Asaba ††Hideo Nakajima
Seiko Epson Corporation
Tadashi Hattori
Seiko Epson Corporation
Akio Takanashi
TK Planning Office(Observer)
Masamitsu Hirayama Brüel & Kjær Division, Spectris Co., Ltd.
Toshikazu Satoh
Brüel & Kjær Division, Spectris Co., Ltd.
Takahiro Tamura
Fujii Sound Techno Co., Ltd.
Shinichi Hanami
JQA (Japan Quality Assurance Organization)
Atsushi Yanase
Nittobo Acoustic Engineering Co., Ltd.
Atsushi Hirata
WAKABAYASHI ACOUSTIC DESIGN CORP.
Daisuke Nishizuru
WAKABAYASHI ACOUSTIC DESIGN CORP.
(Member of working group for investigation of acoustical noise standards and specifications)
Yasuhiro Suzuki
BROTHER INDUSTRIES
Chieko Kobayashi
CANON INC.
Takeshi Shishido
CANON INC.
Yutaka Tsunokami
Fuji Xerox Co., Ltd.
Kazuhiro Hayashi
KONICA MINOLTA, INC.
Hideaki DoyoKYOCERA Document Solutions Inc.
Teruki Sugiura
SHARP CORPORATION(Secretariat)
Shoko Shiramizu
Japan Business Machine and Information System Industries
Association(Sub-leader)(Member)†††

Chairperson of working group for investigations of acoustical noise standards and specifications
Vice-chairperson of working group for investigations of acoustical noise standards and specifications

Document No.
EstablishedEstablished by

Edited byii: JBMIA-TR-28: May, 30 th , 2014
: Working group for investigations of acoustical noise standards andspecifications, Environmental Committee
Sub-working group 2 for improving calibration work of measurement
system: JBMS promotion expert committee, Standardization centre, Japan
Business Machine and Information System Industries AssociationJBMS-TR-28:2014

Contents

Page

Introduction ......................................................................................................................................................... 1
1

Scope ...................................................................................................................................................... 1

2

Terms and definitions ........................................................................................................................... 1

3

Noise test codes for ITT equipment and their trend in revisions ..................................................... 2

3.1

Requirements in the current noise test codes ................................................................................... 2

3.2

Recent trend in standard revision for verifying calibration condition requirements inmeasurement system ............................................................................................................................ 44

Study for variation in sensitivity of microphone by JBMIA SWG2................................................... 4

4.1

Specifications of measurement microphone...................................................................................... 4

4.2

Verification experiment using a reference sound source ................................................................. 5

4.3

Reference sound source as verification method ............................................................................... 6

5

Recommended verification method for calibration conditions in measurement systemusing reference sound source ............................................................................................................. 7

5.1

General ................................................................................................................................................... 7

5.2

Testing environment ............................................................................................................................. 7

5.3

Instrumentation ..................................................................................................................................... 7

5.4

Recommended verification method for calibration conditions in measurement system .............. 7

5.4.1

General ................................................................................................................................................... 7

5.4.2

Pre-test verification ............................................................................................................................... 7

5.4.2.1 Verification using a sound calibrator .................................................................................................. 7
5.4.2.2 Verification using reference sound source ........................................................................................ 7
5.4.3

Mid-test verification - Verification for calibration conditions during test ....................................... 8

5.4.4

Supplemental verification for calibration conditions ........................................................................ 8

5.4.5

Other points to remember .................................................................................................................... 8

Annex A (informative) Guideline for deciding the measurement time interval of reference soundsource ..................................................................................................................................................... 9
A.1

Variation of sound pressure level after power-on.............................................................................. 9

A.2

Stability of time-averaged sound pressure level depending on measurement time interval ........ 9

Bibliography ...................................................................................................................................................... 11iii

JBMIA-TR-28:2014

Blank pageiv

JBMS-TR-28:2014

Recommended verification method forcalibration conditions in multi-channel simultaneous
acoustical noise measurement system
Introduction
For sound power level determinations of information technology and telecommunications equipment(ITT equipment) according to the noise test codes (ISO 7779, ECMA-74, JIS X 7779 etc.), 9 or more
microphone positions are required in a hemi-anechoic chamber (HAC). In this measurement, a multichannel simultaneous acoustical noise measurement system is indispensable not only for theefficiency of workload savings, but also for the improvement of measurement accuracy (repeatability),
especially for the noise sources emitting time-varying noise, such as multifunctional devices, printers,
copy machines, personal computers (PCs) and hard disk drives.
ISO 7779 requires the verification for the calibration conditions of measurement systems by applying asound calibrator to each microphone, once during each series of measurement as daily check. It istrue that the daily calibration work is one of key activities of the measurement routines; however it is avery time-consuming process due to the nature of multi-channel systems.
On the other hand, as long as no significant fluctuation of meteorological condition would occur and all
the measurement systems maintain the wire connection from a microphone to analyzer, it is known
that an impact to the sensitivity of microphones would be negligibly small. And also, this verification
operation may have an influence on measurement results by causing an overload to diaphragm of
microphone depending on the way of inserting microphone to a sound calibrator. Therefore, theverification must be done as less frequent as possible. For these reasons, frequent verification ofcalibration conditions increases not only the workload of operators, but also a risk of damaging
microphones, particularly for the testing laboratories adopting multi-channel simultaneous acousticalnoise measurement system
This time, the Environmental committee of Japan Business Machine and Information System
Industries Association (JBMIA) has organized SWG 2 under the Noise WG (working group forinvestigation of acoustical noise standards and specifications) in January 2012, and has studied for
improving the efficiency of verification of calibration condition not only from the standpoint of
manufacturers of ITT equipment, but also from that of the testing laboratories and the manufacturers ofthe measurement systems. The verification method from this study uses a reference sound source
satisfying the requirements of ISO 6926 for verification instead of a sound calibrator. This new method
could improve time efficiency and verify more than one microphone safely and appropriately, because
it does not touch directly the microphones. This JBMIA-TR reports the method.

1

Scope

This technical report gives information of recommended verification method for the calibration
conditions in a multi-channel simultaneous measurement system to measure sound power level of
acoustical noise from ITT equipment according to noise test codes such as ISO 7779.

2

Terms and definitions

For the purposes of this technical report, the terms and definitions given in ISO 7779 and the following
apply.

1JBMS-TR-28:2014

2.1
reference sound source (RSS)
device which is intended for use as a stable source of sound, and which has a known broad-band
sound power spectrum calibrated in accordance with ISO 6926 over the frequency range of interest
2.2
sound calibrator
device generating one or more known sound pressure levels at one or more frequencies inaccordance with IEC 60942, and of which intended use is to apply to the microphones of specificmodel and configuration
2.3
multi-channel simultaneous acoustical noise measurement systemsystem for measuring acoustical noise with more than one microphone simultaneously especially forthe measurement of time-varying noise such as printers, copiers, personal computers and hard disks
for improving the measurement efficiency and repeatability
2.4
automatic microphone positioning system,
automatic microphone traversing systemsystem for positioning one or more microphones automatically, which adjusts the microphones
precisely and efficiently to the designated positions depending on the size of the noise source under
test

3

Noise test codes for ITT equipment and their trend in revisions

3.1 Requirements in the current noise test codes
For the measurement of acoustical noise emitted from ITT equipment, there are several parallel noise
test codes such as global ISO 7779, industry wide ECMA-74, nation-wide JIS X 7779 for Japan;
ANSI/ASA S12.10 Part 1 for USA; GB/T 18313 for PRC, etc. (See Table 1.)
Table 1 — Noise test codes for ITT equipment
Coverage

Organization (Nation)

GlobalIndustrywide
Nation wide

ISO
Ecma International (Europe basis, but actually global)
JBMIA (Japan)
JISC (Japan)
ANSI/ASA (USA)GB (PRC)KS (Korea)
AS (Australia)

Standard number
ISO 7779:2010 3rd edition
ECMA-74:2012 12th edition a
JBMS-74 series b
JIS X 7779:2012 2nd edition c
ANSI/ASA S12.10-2010 Part 1 d
GB/T 18313:2001 1st edition e
KS I ISO 7779:2002 1st edition f
AS 3755-1990 1st edition gaEquivalent to ISO 7779:2010, 3rd edition + Normative Annex C for specifying operating/installation conditions for manyequipment categories.

b

Supplement to ECMA-74, for specific needs of JBMIAcJapanese translation of ISO 7779:2010, 3rd editiondEquivalent to ISO 7779:2010, 3rd editioneChinese translation of ISO 7779:1999, 2nd editionf

Korean translation of ISO 7779:1999, 2nd editiong

Equivalent to ISO 7779:1988, 1st edition

These noise test codes commonly state alternative test methods for each testing environment;“Method for determination of sound power level of equipment in reverberation test rooms” and “Methodfor determination of sound power levels of equipment under essentially free-field conditions over a

JBMS-TR-28:2014reflecting plane”. The former is so called a reverberation chamber method (RC method), and the latteris so called a hemi-anechoic chamber method (HAC method). For RC method, 6 microphone positions
are required according to ISO 3741, and for HAC method, 9 or more microphone positions are
required according to ISO 3744. (Typical example of microphone arrays on a parallelepiped
measurement surface is shown in Figure 1.) Many testing laboratories (particularly those testing ITT
equipments such as printers, copy machines, PCs and hard disk drives) adopt a multi-channel
simultaneous acoustical noise measurement system and an automatic microphone positioning system
for the following reasons:• Since the most of ITT equipment emit time-varying noise, it is difficult to synchronize themeasurement timing in case that the acoustical noises are to be measured more than once withrepositioning the microphones.
• Because the manual positioning of microphones may increase human errors depending on theoperators’ proficiency levels.
• To improve the efficiency in positioning the microphones because parallelepiped measurement
surface shall always be adjusted depending on the dimensions of the noise source under test.
• To ease the quantification of measurement uncertainty by referring the specifications of theautomatic microphone positioning system.

Figure 1 — Example of Microphone arrays on parallelepiped measurement surface(excerpted from ISO 3744:2010)
On the other hand, the existing noise test codes such as ISO 7779 commonly requires the verificationof the entire measurement system by physical contact with applying sound calibrator to microphones
once during each series of measurements as follows.
7.4.6 Calibration
During each series of measurements, a sound calibrator as specified in IEC 60942, class 1,
shall be applied to the microphone to verify the calibration of the entire measurement system
at one or more frequencies over the frequency range of interest.
Therefore, according to such noise test codes, the testing laboratories are required to verify calibration
conditions as one of the key routine activities of every measurement day, although such verification
operations consume a lot of time and may have a risk of damaging microphones.

3

JBMIA-TR-28:2014

3.2 Recent trend in standard revision for verifying calibration condition requirements
in measurement system
When the noise test codes such as ISO 7779 is revised, Guide 1 of ISO/TC43/SC1 is the mostinfluential document on it. At the time of development of this JBMIA-TR, the requirement of“calibration” in the document is as follows.
X.1.2 Calibration
At the beginning and at the end of every measurement session and at least at the beginningand the end of each measurement day the entire sound pressure level measuring system shallbe checked at one or more frequencies by means of a sound calibrator meeting therequirements for a class X instrument according to IEC 60942. Without any further adjustment
the difference between the readings of two consecutive checks shall be less or equal to 0,5
dB. If this value is exceeded the results of measurements obtained after the previous
satisfactory check shall be discarded.
NOTE 1 In “class X“, “class 1” or “class 2” is inserted accommodating noise test code applying thisrequirement.
NOTE 2 In this excerpt, ”,” is used for decimal point according to Guide 1.
Thus, Guide 1 requires testing laboratories to verify calibration condition of the entire measurement
system “at the beginning and at the end of every measurement session”. Though the present noise
test codes such as ISO 7779 requires “once during each series of measurements,” the testinglaboratories having multi-channel simultaneous measurement system will have to verify, at least, 6
microphones for RC method and 9 or more microphones for HAC method twice a day, if therequirements of Guide 1 are adapted to the noise test code such as ISO 7779. This means that the
microphones shall be verified 18 times or more every measurement day for HAC method. Such a timeconsuming daily operation does not look practical.

4

Study for variation in sensitivity of microphone by JBMIA SWG2

4.1 Specifications of measurement microphone
JBMIA has organized SWG 2 under the Noise WG, and has studied for improving the efficiency ofverification of calibration condition from various standpoints not only from the manufacturers of ITT
equipment, but also the testing laboratories and the manufacturers of measurement systems. SWG2
inquired the manufacturers of microphones and sound calibrators about their specifications related toverification regardless that if they are a member of SWG2 or not. As the results, SWG2 has noticed
some common issues as follows:• Verification operation may have an influence on the measurement results because it may cause
an overload to the microphone diaphragm depending on the way of inserting a microphone to asound calibrator. Therefore, the insertion must be done carefully as less frequent as possible.
• The manufacturers of the sound calibrator assume that a microphone is inserted vertically to asound calibrator which is placed on a stable place such as on a desk. Thus, it is not assumed andhas difficulty in that the microphone fastened to the manipulator of the automatic microphone
positioning system.
• As long as all the measurement systems maintain the wire connection from microphone toanalyzer, an impact to the sensitivity of microphones should be very small or negligible.
From the above, provided that there are no significant fluctuation of meteorological conditions(temperature, humidity and atmospheric pressure) and the wire connection from microphone to4

JBMS-TR-28:2014

analyzer are maintained, two times of the verification operations, i.e., both before and after ameasurement session, would not be necessary.
If the two verifications before and after a measurement are applied to noise test codes such as ISO
7779 for the testing laboratories adopting multi-channel simultaneous acoustical noise measurement
system, not only the daily verification workload will be increased twice but also the failure risks will be
increased by the number of microphones.

4.2 Verification experiment using a reference sound source
SWG2 have conducted an experiment inspecting the fluctuation of the measurement results for 5
consecutive days in order to demonstrate that the sensitivity of microphone would fluctuate little or be
negligible as long as the entire measurement systems maintain wire connection, even though longtime would be passed.
A reference sound source (RSS) was used as the test sound source of this experiment. The technicalrequirements of a RSS are specified in ISO 6926 and it is usually designed and calibrated to satisfy
the standard deviation of repeatability of 0.2 dB for one-third-octave band sound power level of 1 kHz(see Table 2). From measurement experiences of the members of SWG2, it was known that a RSS
also has good repeatability for sound pressure level (measured) at every microphone position.
Table 2 — Maximum value of the standard deviation of the sound power level under
repeatability conditions for reference sound source according to ISO 6926 (excerpt)

Other conditions were as follows:• The RSS was measured once a day with the entire measurement systems maintaining the wire
connections from microphone to analyzer for the entire test days, but the systems were
electrically powered on and off every day.
• According to ISO 3744, the microphones were positioned over the parallelepiped measurement
surface with the reference box of the RSS, 30 cm ×30 cm ×30 cm and the measurement
distance, d = 1.0 m.
• All the microphones were verified with a sound calibrator only before the measurement of the firstday and after the measurement of the last day.
• A CVCF (Constant Voltage – Constant Frequency unit) was used for the main power supply to the
RSS. The RSS was operated for 5 min before its daily sound power level determination, and thetime-averaged sound pressure level of 30 s was measured at each microphone position. This RSS
has been checked its conformance to ISO 6926 once a year.
• Microphones were re-positioned by the automatic microphone positioning system every day andthe RSS was also re-positioned every day.
• The measurement results were shown as those of 1 kHz one-third-octave band because thesound calibrator with 1 kHz nominal frequency was used.
• Corrections due to the reference meteorological conditions were not applied.

5

JBMIA-TR-28:2014

Deviation [dB]

0.3
0.2
0.1
0.0
-0.1
-0.2
-0.3

0.3
0.2
0.1
0.0
-0.1
-0.2
-0.3

0.3
0.2
0.1
0.0
-0.1
-0.2
-0.3

1

2

3

Deviation [dB]
4

Day

5

microphone 2

1

2

3

Deviation [dB]

0.3
0.2
0.1
0.0
-0.1
-0.2
-0.3

microphone 1

4

Day

5

microphone 3

1

2

3

Deviation [dB]

0.3
0.2
0.1
0.0
-0.1
-0.2
-0.3

4

Day

5

microphone 4

1

2

3

Day

Deviation [dB]

Deviation [dB]

Deviation [dB]

Deviation [dB]

Deviation [dB]

Fluctuation of the sound pressure levels on each microphone is shown in Figure 2. Figure 3 shows thesound power level calculated from the sound pressure levels of all the 9 measurement points todemonstrate the stability of the RSS.

4

5

4

5

0.3
0.2
0.1
0.0
-0.1
-0.2
-0.3

0.3
0.2
0.1
0.0
-0.1
-0.2
-0.3

0.3
0.2
0.1
0.0
-0.1
-0.2
-0.3

0.3
0.2
0.1
0.0
-0.1
-0.2
-0.3

microphone 6

1

2

3

Day

4

5

4

5

4

5

4

5

microphone 7

1

2

3

Day

microphone 8

1

2

3

Day

microphone 9

1

2

3

Day

microphone 5

1

2

3

Day

Deviation [dB]

Figure 2 — Fluctuation of 1 kHz one-third-octave band sound pressure level on eachmicrophone, reference to day 1 (The microphone numbers correspond to Figure 1.)
0.3
0.2
0.1
0.0
-0.1
-0.2
-0.3

1

2

3

Day

4

5

Figure 3 — Fluctuation of 1 kHz one-third-octave band sound power level(reference to day 1)
As shown in Figure 2, the maximum fluctuation of sound pressure levels on each microphone was
0.21 dB and every microphone has good stability.

4.3 Reference sound source as verification method
The RSS could be used as a tool for verifying the calibration conditions by comparing themeasurement results of validation of 4.2, instead of a sound calibrator. This would also be verificationof the compliance to the requirement of Guide 1 that “the difference between the readings of twoconsecutive checks shall be less or equal to 0.5 dB.” However, it requires the verification of soundpressure level, not sound power level, per microphone.

6

JBMS-TR-28:2014

This method has the following advantages:• This method allows verification without any physical contact to a microphone; which would prevent
microphones from being damaged.
• This method allows verification with any one-third-octave band; while the existing method using asound calibrator only allows the verification for a single frequency.

5 Recommended verification method for calibration conditions inmeasurement system using reference sound source
5.1 General
This clause states the recommended verification method for calibration conditions in measurement
system on the basis of the above studies.

5.2 Testing environment
The requirements of the noise test codes shall be followed, as applicable. In this measurement, it isrecommended to hold the temperature and the humidity stable. And especially if the noise source
under test is low noise equipment, it is also recommended to confirm it before or after microphonesensitivity measurement by RSS that the background noise of the testing environment is sufficiently
low.

5.3 Instrumentation
In case that the verification method in this JBMIA-TR is used, it is strongly recommended to maintainwire connection of each microphone, pre-amplifier and cables for the entire test period, while themeasurement systems do not need maintaining powered on electrically. Additionally, it is also
recommended to check the internal noise of the measurement systems before test.

5.4 Recommended verification method for calibration conditions in measurement
system5.4.1

GeneralVerification method recommended in this JBMIA-TR consists of “pre-test verification” and “mid-test
verification” that is verification for calibration conditions during test. “Pre-test verification” is executed
before the first measurement after the measurement systems are wire connected. “Mid-test
verification” is executed after pre-test verification. It is expected that the specific timing of “mid-test
verification” would be stipulated in a noise test code in which this verification method could be
introduced.
5.4.2

Pre-test verification

5.4.2.1 Verification using a sound calibrator
A sound calibrator is applied to the microphone to verify the calibration of the entire measuring system
at one or more frequencies over the frequency range of interest in accordance with the requirementsof noise test code.
5.4.2.2 Verification using reference sound source
After the verification using a sound calibrator is completed, a RSS is positioned in testing environment.
If noise source under test could not be put out during a measurement session, a RSS could not be
positioned in the center of the test room as long as positional relationship between the noise source
under test, microphones and RSS could be duplicated at any timing of test. The RSS is operated in the

7

JBMIA-TR-28:2014

same manner as those calibrated in accordance with ISO 6926. After the rotating speed becomesstable, one-third-octave band time-averaged sound pressure levels over the frequency range ofinterest are measured at each microphone (for decision methods of operating time after power-on andaveraging time are referred in Annex A). These measurement values become reference of subsequentverification. One-third-octave band frequency which includes the frequency verified in 5.4.2.1 isverified. The other frequency band data could be used to verify that characteristic of every microphone
is not changed due to breakage, for example. After recording the information to duplicate the positional
relationship, RSS is removed from the test chamber.
5.4.3

Mid-test verification - Verification for calibration conditions during test

Microphones and RSS are positioned at the same locations as in 5.4.2.2. In case that the testinglaboratory chose not to change the location of the noise source under test, all positions including thenoise sound source should be duplicated. After RSS is operated and rotating speed become stable,
the time-averaged sound pressure level same as 5.4.2.2 is measured by every microphone. By
comparing these measured values with the reference values measured in 5.4.2.2 and as long as thedifferences are within 0.5 dB, the microphones are verified that they are functioning correctly at thisfrequency. From this point onward, testing laboratories can verify their calibration conditions byexecuting this verification.
5.4.4

Supplemental verification for calibration conditions

If the verification using a RSS is not sufficient since, for example, microphones are damaged by acertain reason during a measurement, the testing laboratories can verify the entire measurement
systems by applying a sound calibrator to every microphone as described in 5.4.2.1, as appropriate.
5.4.5

Other points to remember

Since a significant variation of atmospheric pressure affects the measurement values, it can be
possible to correct the measurement values according to the referenced meteorological conditions, as
appropriate. However, it is limited and supposed that the same method is applied to both 5.4.2.2 and5.4.3.

8

JBMS-TR-28:2014

Annex A
(informative)
Guideline for deciding the measurement time intervalof reference sound source
In the verification method for calibration conditions using a RSS recommended by this JBMIA-TR, it iseffective to evaluate the stability of the RSS in advance and to decide proper measurement timeinterval of it in the individual testing laboratories. This annex presents the evaluation results of thevariation of sound pressure level after power-on and the stability of time-averaged sound pressurelevel depending on the measurement time interval of the calibrated RSS in accordance with ISO 6926.

A.1

Variation of sound pressure level after power-on

Figure A.1 shows an example of time variation of the sound pressure level after the power-on of a
RSS. Since the evaluated RSS generated sound by using an AC fan, a CVCF was used for theelectrical power supply. Figure A.1 shows the result of 100 Hz – 10 000 Hz at one of the 9
microphones for A-weighted sound pressure level positioned as the same as the sound power levelmeasurement, the results of the other 8 microphones showed the similarity to Figure A.1. Since thisresult shows that the RSS was operated sufficiently stable when 30 s passed after power-on, themeasurement productivity should not be spoiled by applying the recommended verification method inthis JBMIA-TR.
90

Sound Pressure Level [dB]

80
70
60
50
40
30

0

30

60

90

120

150

180

210

240

270

300

Time [s]Figure A.1 — Variation of sound pressure level after power-on(A-weighted level)

A.2
Stability of time-averaged sound pressure level depending on measurement
time interval
Figure A.2 shows an example of the standard deviations of sound pressure level which was measured
5 times with different measurement time intervals. The Figure shows the standard deviations of the
maximum and the average value of 1 kHz center frequency of one-third-octave band at the 9
microphone positions of sound power level measurement. In order to evaluate the characteristic of the
RSS, the RSS had been continuously operated through all the measurements. All the measurements
were executed consecutively and the positions between the RSS and the microphones were not

9

JBMIA-TR-28:2014changed. From this result, the measurement value was found sufficiently stable at the equal to or morethan 30 s, and more stable measurement result could be obtained if longer the measurement timeinterval becomes.
0.15

maximumStandard eviation [dB]

average
0.10

0.05

0.00

0

30

60

90

120

150

180

Averaging time [s]Figure A.2 — Stability of time-averaged sound pressure level depending on measurement timeinterval (at 1 kHz 1/3 octave band)
NOTE In case of an aerodynamic method type RSS with using fan, the generated sound pressurelevel should be depending on the rotating speed of the fan that is led by voltage and frequency of thepower-supply. The testing laboratories can confirm if or not the RSS is operated as expected andgenerating the proper sound power level stably with using a contactless (photoelectric) revolution
indicator,. This is effective when a question would arise in the sound power level of the RSS or when
the setting of power supply voltage is changed on the RSS.

10

JBMS-TR-28:2014

Bibliography[1] ISO 3741, Acoustics — Determination of sound power levels and sound energy levels of noise
sources using sound pressure — Precision methods for reverberation test rooms[2] ISO 3744, Acoustics — Determination of sound power levels and sound energy levels of noise
sources using sound pressure — Engineering methods for an essentially free field over areflecting plane[3] ISO 6926, Acoustics — Requirements for the performance and calibration of reference soundsources used for the determination of sound power levels
NOTE

JIS counterpart, JIS Z 8739:2001 (IDT) exists.

[4] ISO 7779:2010, Acoustics — Measurement of airborne noise emitted by information technology
and telecommunications equipment
NOTE

JIS counterpart, JIS X 7779:2012 (IDT) exists.

[5] IEC 60942:2003, Electroacoustics — Sound calibrators
NOTE

JIS counterpart, JIS C 1515:2004 (IDT) exists.

[6] Guide 1, Guide for drafting instrumentation requirements in documents prepared by ISO/TC
43/SC1 “Noise” (Edition2), N 1916, October 2012[7] ECMA-74, Measurement of airborne
telecommunications equipmentnoiseemittedbyinformation

technology

and[8] Shimoda, K., Kimizuka, I., Tashiro, S., Tanaka, K. Considerations for improving the efficiency ofdaily calibration work of multi-channel simultaneous measurement system for sound power level
determination, In: Proceedings of Noise-con 2013, Denver, CO, 2013-08-26/28, N044. Instituteof Noise Control Engineering of the USA, Indianapolis

11