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May 2005

Volume 117, Issue 5, pp. 2671-3330

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Time reversal of noise sources in a reverberation room

Guillemette Ribay, Julien de Rosny, and Mathias Fink

J. Acoust. Soc. Am. Volume 117, Issue 5, pp. 2866-2872 (2005); (7 pages) | Cited 8 times

Online Publication Date: 28 Apr 2005

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Usually, time reversal is studied with pulsed emissions. Here, the properties of time reversal of the acoustic field emitted by noise sources in a reverberation room are studied numerically, theoretically, and experimentally. A time domain numerical simulation of a two-dimensional enclosure shows that the intensity of a time-reversed noise is strongly enhanced right on the initial source position. A theory based on the link that exists between time reversal of noise and the “well-known” time reversal of short pulse is developed. One infers that the focal spot size equals half a wavelength and the signal to noise ratio only depends on the number of transceivers in the time reversal mirror. This last property is characteristic of the time reversal of noise. Experimental results are obtained in a 5×3×3 m3 reverberation room. The working frequency range varies from 300 Hz to 2 kHz. The ability of the time reversal process to physically reconstruct the image of two noise sources is studied. To this end, care is given to the technique to separate two close random sources, and also to the influence of temperature fluctuations on the focusing quality. © 2005 Acoustical Society of America.
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43.55.Br Room acoustics: theory and experiment; reverberation, normal modes, diffusion, transient and steady-state response
43.50.Yw Instrumentation and techniques for noise measurement and analysis
43.20.Ye Measurement methods and instrumentation

Acoustic analysis in Mudejar-Gothic churches: Experimental results

Miguel Galindo, Teófilo Zamarreño, and Sara Girón

J. Acoust. Soc. Am. Volume 117, Issue 5, pp. 2873-2888 (2005); (16 pages) | Cited 10 times

Online Publication Date: 28 Apr 2005

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This paper describes the preliminary results of research work in acoustics, conducted in a set of 12 Mudejar-Gothic churches in the city of Seville in the south of Spain. Despite common architectural style, the churches feature individual characteristics and have volumes ranging from 3947 to 10 708 m3. Acoustic parameters were measured in unoccupied churches according to the ISO-3382 standard. An extensive experimental study was carried out using impulse response analysis through a maximum length sequence measurement system in each church. It covered aspects such as reverberation (reverberation times, early decay times), distribution of sound levels (sound strength); early to late sound energy parameters derived from the impulse responses (center time, clarity for speech, clarity, definition, lateral energy fraction), and speech intelligibility (rapid speech transmission index), which all take both spectral and spatial distribution into account. Background noise was also measured to obtain the NR indices. The study describes the acoustic field inside each temple and establishes a discussion for each one of the acoustic descriptors mentioned by using the theoretical models available and the principles of architectural acoustics. Analysis of the quality of the spaces for music and speech is carried out according to the most widespread criteria for auditoria. © 2005 Acoustical Society of America.
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43.55.Gx Studies of existing auditoria and enclosures
43.55.Mc Room acoustics measuring instruments, computer measurement of room properties
43.58.Gn Acoustic impulse analyzers and measurements
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