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Acoustical noise measurement and control in electronic systems
Published in Kaveh Azar, in Electronic Cooling, 2020
George C. Maling, David M. Yeager
A second procedure standardized nationally in ANSI S1.31 and S1.32 and internationally in ISO 3741 and ISO 3742 is to use the comparison method in a reverberation room. A reverberation room is a specially designed facility with surfaces which are highly reflective for sound. In such a facility, the reflections from the room surfaces make the sound pressure level relatively independent of the position of the measuring microphone in the room. Using this method, the mean square sound pressure averaged in space and time is determined in the reverberation room for both the source under test and a reference sound source having a known sound power output. The average sound pressure level in the room is usually determined using a microphone which moves in an arc or on a circular path in the room. Determination of sound pressure levels averaged in space and in time is done in octave or one third octave bands with a commercially available real time sound analyzer. The sound power level of the source is given by () LWS=LWR+0.1(LpS−LpR)
Architectural Acoustics
Published in Malcolm J. Crocker, A. John Price, Noise and Noise Control, 2018
Malcolm J. Crocker, A. John Price
The International Standards Organization also has set a testing standard for reverberation room absorption testing under ISO Recommendation 354, "Measurement of Absorption Coefficients in a Reverberation Room." The size of the testing chamber is again governed by the lowest test frequency desired, but in order to measure down to 100 Hz the room should be in excess of 225 m3 (7,945 ft3) and also satisfy V > 13/6.8, where 1 is the greatest diagonal length of the room. The sample size is restricted to rectangular plane samples of area from 10 m2 to 12 m2 (i.e., 108 to 130 ft2). Strips of materials are to be avoided and the ratio of sample length to breadth must be not less than 0.7. The reverberation times of the test room itself must exceed 5 sec at 125, 250 and 500 Hz, 4.5 sec at 1,000 Hz, 3.5 sec at 2,000 Hz and 2 sec at 4,000 Hz. Either one third or one half octave bands of white noise may be used and warble tones may also be used, provided the frequency of deviation from the tone is ± 10% for ⩽ 500 Hz and ± 50 Hz for > 500 Hz — the modulation frequency being set at 6 Hz. The use of stationary or rotating vane diffusers is again recommended.
Introduction to room acoustics
Published in Jens Holger Rindel, Sound Insulation in Buildings, 2018
A reverberation room can be used to determine the sound power of a sound source by measuring the average sound pressure level in the room. If measurements are made in positions that avoid the direct sound, the last term in Equation 4.44 becomes more correctly (Vorländer 1995):10lg(1−αm)→10lg(e−AS)≅−4.34⋅AS(dB)
Acoustic properties of sound-absorbing polyester fabrics woven with thick staple and thin draw textured yarn for use in interior decoration
Published in The Journal of The Textile Institute, 2019
YoungA Kang, EunNyeong Lee, KwanChul Lee, SoonMo Choi, EunJoo Shin
Reverberant field methods. The random-incidence sound absorption was measured by a method similar to that described in ISO 354-2003, KS F 2805:2014, and ASTM C 423-2009a. The sound absorption coefficients were measured by the reverberation-room method at 1/3 octave intervals in the frequency range of 100–5000 Hz based on the ISO (354-2003) standard. For this method, a special reverberation room was used. The volume of the reverberation room was 220 m3 and its shape was irregular. The set-up area of the test specimen was 11.4 m2. The air temperature and relative humidity in the chamber were 20.4 ± 2 °C and 65 ± 5%, respectively. The sound absorption coefficient of the test fabric was evaluated from the reverberation time measured by the method described in ISO 354:2003 according to the following formula,