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v3.1, 20040329, ME

Session S Tuesday, May 11 13:00 h–16:00 h
Chair: Ernst-Joachim Völker, Institute for Acoustics and Building Physics, Oberursel and Zweihausen, Germany

S-1 Sound Conditioning in Open-Plane Offices—40 Years under Stress?Wolfgang Teuber; Ernst-Joachim Völker, Institute for Acoustics and Building Physics, Oberursel and Zweihausen, Germany
Masking effects are well known and are increasingly used to cover disturbing noise. Data reduction cuts out useless signals that are not audible. In an office environment masking means privacy. But masking sound must follow strict rules. The Acoustical Field of Confidence describes the parameters, such as interfering noise, distance to next working places, intelligibility of speech, acoustical conditions, and the level of masking noise, e.g., around 45 dB(A). “The Steps of Privacy” include the different types of office work. The masking sound must be of special shape to fulfill the purposes, above all not to disturb. The paper deals with open-plane offices that have had a constant background noise for the past 40 years. Measurements have been carried out once a year to check the levels and acoustical properties. Since the beginning of testing, there have been no complaints and no stress for the people working there.
S-2 Finite-Difference Time-Domain Acoustic Analysis of Fibrous Sound-Absorbing MaterialsJosé Escolano, Basilio Pueo, Sergio Bleda, University of Alicante, Alicante, Spain
A Finite-Difference Time-Domain (FDTD) method was successfully developed to model electromagnetic systems. Since acoustics and electromagnetism share certain undulatory properties, a natural adaptation of this technique has been developed as well. Several acoustics problems require the use of fibrous tangles to attenuate the propagation speed of sound waves, such as room acoustics. Notwithstanding, although free air acoustic propagation is known, FDTD technique is not developed yet to model fibrous materials. To characterize this behavior only a few and measurable set of parameters must be considered. In this paper a new approach for modeling fibrous materials analysis using FDTD is presented and validated. A set of simulations covering various different materials is performed, including some real fiberglass cases.
S-3 Reverberation Control in an Auditorium Using Loudspeaker Array—Kazuho Ono1, Kimio Hamasaki1, Setsu Komiyama1, Sumi Sakumoto2, Juro Ohga3
NHK Science and Technical Research Laboratories, Tokyo, Japan
Cosmo Space
Shibaura Institute of Technology, Tokyo, Japan
An electroacoustic reverberation control system is used mainly for multipurpose auditoriums or concert halls whose acoustical designs are not ideal for music performance. The present paper discusses the use of loudspeaker arrays for electroacoustical reverberation control in an auditorium, especially the effect of using multiple loudspeakers on a listening area. The experiment was conducted in our new auditorium equipped with 7 vertical pillar-type loudspeaker arrays for each sidewall of the auditorium. Subjective evaluation tests for lateral balance was conducted with various loudspeaker setups and listening points, including off-center ones. The results were compared with sound pressure distribution created by corresponding loudspeaker setups, based on the criteria of setting loudspeakers to large listening areas.
S-4 Room Acoustics and Equalization of Loudspeaker Systems for Multipurpose Mixing TheatersAndrew Munro, Munro Acoustics Ltd. And Dynaudio Acoustics, London, UK
For many years a series of equations have been used to design and predict the performance of sound systems and acoustic environments based on statistically diffused sound fields and idealized directivity patterns. Although these equations have been modified for semi-reverberant spaces, there is a significant error produced by the strength of both early reflections and room modes. A comparison of theory and measurement applied to film mixing theaters leads to some interesting conclusions.
S-5 Implementation of a Nonlinear Room Impulse Response Estimation AlgorithmTim Collins, University of Birmingham, Birmingham, UK
Most techniques for estimating the transfer function (or impulse response) of an acoustical space with a high signal-to-noise ratio operate along similar principles. A known, broadband signal is transmitted at one point in the room while being simultaneously recorded at another. A matched-filter is then used to compress the transmission waveform into an approximate impulse, and equalization filtering is used to remove any coloration caused by the nonuniform energy-spectrum of the transmission and/or the nonideal response of the loudspeaker/microphone combination. In this paper the limitations of this conventional technique will be highlighted, especially when using low-cost equipment. An alternative, nonlinear deconvolution technique is proposed, which will be shown to give superior performance using both synthetic waveforms and practical room measurements.
S-6 Influence of Ray Angle of Incidence and Complex Reflection Factor on Acoustical Simulation ResultsEmad El-Saghir1, Stefan Feistel2
Acoustic Design Ahnert Limited, Cairo, Egypt
SDA Software Design Ahnert GmbH, Berlin, Germany
Many ray tracing algorithms make use of the single-valued diffuse-field absorption coefficient to simulate the sound field in a given room computer model. They consider, however, neither the effect of the angle of incidence nor the fact that the reflection factor is complex. If characteristic impedance and wave number, which are measured in an impedance tube, are known, we can expect reflectograms, which look different from those generated by current simulators, and look different for different thicknesses. This paper investigates how much the angle-dependent reflectograms, which consider phase shift due to complex reflection factors, look different from the angle-independent ones respectively, and whether the statistical nature of reflectograms leads to the cancellation of such effects.

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