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GB/T 20247-2006 PDF in English


GB/T 20247-2006 (GB/T20247-2006, GBT 20247-2006, GBT20247-2006)
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GB/T 20247-2006: PDF in English (GBT 20247-2006)

GB/T 20247-2006
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 17.140
A 59
GB/T 20247-2006 / ISO 354:2003
Acoustics – Measurement of Sound Absorption in a
Reverberation Room
(ISO 354:2003, IDT)
ISSUED ON: MAY 08, 2006
IMPLEMENTED ON: NOVEMBER 01, 2006
Issued by: General Administration of Quality Supervision, Inspection and
Quarantine;
Standardization Administration of the People’s Republic of China.
Table of Contents
Foreword ... 3
Introduction ... 4
1 Scope ... 5
2 Normative References ... 5
3 Terms and Definitions ... 5
4 Principle ... 7
5 Frequency Range ... 7
6 Test Arrangement ... 8
6.1 Reverberation room and diffusion of sound field ... 8
6.2 Test specimens ... 9
6.3 Temperature and relative humidity ... 10
7 Measurement of Reverberation Time ... 10
7.1 General ... 10
7.2 Interrupted noise method ... 11
7.3 Integrated impulse response method ... 13
7.4 Evaluation of reverberation times based on decay curves ... 16
8 Expression of Results ... 16
8.1 Method of calculation ... 16
8.2 Precision ... 18
8.3 Presentation of results ... 19
9 Test Report ... 20
Annex A (Normative) Diffusivity of the Sound Field in the Reverberation Room ... 21
Annex B (Normative) Test Specimen Mountings for Sound Absorption Tests ... 23
Annex C (Informative) Bibliography ... 30
Foreword
This Standard equivalently adopts ISO 354:2003 Acoustics – Measurement of Sound
Absorption in a Reverberation Room.
When this Standard equivalently adopts the international standard, partial terms and definitions
shall refer to GB/T 3947-1996 Acoustical Terminology.
This Standard’s Annexes A and B are normative; while Annex C is informative.
This Standard was proposed by Chinese Academy of Sciences.
This Standard shall be under the jurisdiction of National Technical Committee on Acoustics of
Standardization Administration of China (SAC/TC 17).
Drafting organizations of this Standard: China Central Radio, Film & Television Design and
Research Institute; and Institute of Acoustics, Chinese Academy of Sciences.
Chief drafting staffs of this Standard: Chen Huaimin, Zhang Mingzhao, Luo Xuecong, Chen
Jianhua, and Lv Yadong.
Acoustics – Measurement of Sound Absorption in a
Reverberation Room
1 Scope
This Standard specifies a method of measuring the sound absorption coefficient of acoustical
materials used as wall or ceiling treatments, or the equivalent sound absorption area of objects,
such as furniture, persons or space absorbers, in a reverberation room. It is not intended to be
used for measuring the absorption characteristics of weakly damped resonators.
The results obtained can be used for comparison purposes and for design calculation with
respect to room acoustics and noise control.
2 Normative References
The provisions in following documents become the provisions of this Standard through
reference in this Standard. For dated references, the subsequent amendments (excluding
corrigendum) or revisions do not apply to this Standard, however, parties who reach an
agreement based on this Standard are encouraged to study if the latest versions of these
documents are applicable. For undated references, the latest edition of the referenced document
applies.
GB/T 3240-1982 Preferred frequencies for the acoustical measurement
GB/T 3241 Octave-band and fractional-octave-band filters (GB/T 3241-1998, eqv IEC
61260-1995)
GB/T 17247.1 Acoustics - Attenuation of sound during propagation outdoors - Part 1:
Calculation of the absorption of sound by the atmosphere (GB/T 17247.1-2000, eqv ISO
9613-1:1993)
3 Terms and Definitions
For the purposes of this Standard, the following terms and definitions apply.
3.1 Decay curve
Graphical representation of the decay of the sound pressure level in a room as a function of
It is, however, possible to generate band-filtered pulses. One practice that works well is to feed the
loudspeaker system with the time-reversed impulse response of a bandpass filter, i.e., a one-third-octave
band filter.
7.3.2 Indirect method
Special sound signals may be used which yield the impulse response only after special
processing of the microphone signal. This can provide an improved signal-to-noise ratio. Tone
sweeps or pseudo-random noise (e.g., maximum-length sequences) may be used if the
requirements for the spectral characteristics of the source are fulfilled. Because of the gain in
signal-to-noise ratio, the dynamic requirements of the source may be considerably lower than
those set in 7.3.1. If synchronized time averaging is used (e.g., in order to enhance the signal-
to-noise ratio), it is necessary to verify that the impulse response remains unchanged during the
whole measurement process. The signals may be generated by devices that will consist either
of external hard- and software, or devices that form an integrated part of the measuring device.
The bandwidth of the signal shall be greater than one-third octave. The spectrum should be
reasonably flat within the actual one-third-octave band to be measured. Alternatively, the
broadband noise spectrum may be shaped to provide an approximately pink spectrum in the
range covering the one-third-octave bands with midband frequencies from 100 Hz to 5 kHz,
with the reverberation time being measured simultaneously in different one-third-octave bands.
The test signal shall be such that the resulting decay curve for the respective frequency band
meets the level requirements given in 7.2.1.
7.3.3 Recording system
The recording system shall consist of microphones and amplifiers satisfying the requirements
given in 7.1.2 and 7.2.3, as well as an additional device that is capable of digitalizing the
recorded signal and of performing all the necessary data processing, including the integration
of the impulse response and the evaluation of the decay curve. In the case of 7.3.2, the recording
system may also contain the necessary hardware and software to process the impulse response
from the recorded signal and also to generate the test signal.
The impulse response shall be filtered in one-third-octave bands. The filtering may be processed
before or after the digitalization of the impulse response, but in any case, before performing the
integration. Analog or digital filters may be used. The filters shall conform to GB/T 3241.
NOTE: The use of special test signals, such as maximum length sequences, not only requires more
sophisticated data processing, but also a deeper knowledge of the theoretical background in order to
obtain proper results. Since a detailed introduction to this technique is outside scope of this Standard, the
user should refer to appropriate literature.
7.3.4 Integration of the impulse response
The filtered impulse response shall be backward integrated. The result is theoretically
equivalent to an infinite number of averaged decays obtained by the interrupted noise method.
......
 
Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.