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AES New York 2007
Paper Session P13

P13 - Acoustic Modeling, Part 1

Sunday, October 7, 8:30 am — 12:30 pm
Chair: Kurt Graffy, Arup Acoustics - San Francisco, CA, USA

P13-1 Addressing the Discrepancy Between Measured and Modeled Impulse Responses for Small RoomsZhixin Chen, Robert Maher, Montana State University - Bozeman, MT, USA
Simple computer modeling of impulse responses for small rectangular rooms is typically based on the image source method, which results in an impulse response with very high time resolution. Image source method is easy to implement, but simulated impulse responses are often a poor match to measured impulse responses because descriptions of sources, receivers, and room surfaces are often too idealized to match real measurement conditions. In this paper a more elaborate room impulse response computer modeling technique is developed by incorporating measured polar responses of loudspeaker, measured polar responses of microphone, and measured reflection coefficients of room surfaces into basic image source method. Results show that compared with basic image source method, the modeled room impulse response using this method is a better match to the measured room impulse response, as predicted by standard acoustical theories and principles.
Convention Paper 7239 (Purchase now)

P13-2 Comparison of Simulated and Measured HRTFs: FDTD Simulation Using MRI Head DataParham Mokhtari, Hironori Takemoto, Ryouichi Nishimura, Hiroaki Kato, NICT/ATR - Kyoto, Japan
This paper presents a comparison of computer-simulated versus acoustically measured, front-hemisphere head related transfer functions (HRTFs) of two human subjects. Simulations were carried out with a 3-D finite difference time domain (FDTD) method, using magnetic resonance imaging (MRI) data of each subject’s head. A spectral distortion measure was used to quantify the similarity between pairs of HRTFs. Despite various causes of mismatch including a different head-to-source distance, the simulation results agreed considerably with the acoustic measurements, particularly in the major peaks and notches of the front ipsilateral HRTFs. Averaged over 133 source locations and both ears, mean spectral distortions for the two subjects were 4.7 dB and 3.8 dB respectively.
Convention Paper 7240 (Purchase now)

P13-3 Scattering Uniformity Measurements and First Reflection Analysis in a Large Nonanechoic EnvironmentLorenzo Rizzi, LAE - Laboratorio di Acustica ed Elettroacustica - Parma, Italy; Angelo Farina, Università di Parma - Parma, Italy; Paolo Galaverna, Genesis Acoustic Workshop - Parma, Italy; Paolo Martignon, Andrea Rosati, Lorenzo Conti, LAE - Laboratorio di Acustica ed Elettroacustica - Parma, Italy
A new campaign of experiments was run on the floor of a large room to obtain a long enough anechoic time window. This permitted us to study the first reflection from the panels themselves and their diffusion uniformity. The results are discussed, comparing them with past measurements and with the ones from a simplified set-up with a smaller geometry. Some key matters to measurement are discussed; they were proposed in a recent comment letter posted to the specific AES-4id document committee on its reaffirmation. An analysis of the single reflection and reflectivity data was undertaken to investigate the behavior of a perforated panel and the measurement set-up overall potential.
Convention Paper 7241 (Purchase now)

P13-4 A Note On the Implementation of Directive Sources in Discrete Time-Domain Dispersive Meshes for Room Acoustic SimulationJosé Escolano, University of Jaén - Jaén, Spain; José J. López, Technical University of Valencia - Valencia, Spain; Basilio Pueo, University of Alicante - Alicante, Spain; Maximo Cobos, Technical University of Valencia - Valencia, Spain
The use of wave methods to simulate room impulse responses provides the most accurate solutions. Recently, a method to incorporate directive sources in discrete-time methods, such as finite differences and digital waveguide mesh has been proposed. It is based in the proper combination of monopoles in order to achieve the desired directive pattern in far field conditions. However, this method is used without taking into account the inherent dispersion in most of these discrete-time paradigms. This paper analyzes how influent is the dispersion in order to get the proper directivity through different study cases.
Convention Paper 7242 (Purchase now)

P13-5 Rendering of Virtual Sound Sources with Arbitrary Directivity in Higher Order AmbisonicsJens Ahrens, Sascha Spors, Technical University of Berlin - Berlin, Germany
Higher order Ambisonics (HOA) is a spatial audio reproduction technique aiming at physically synthesizing a desired sound field. It is based on the expansion of sound fields into orthogonal basis functions (spatial harmonics). In this paper we present an approach to the two-dimensional reproduction of virtual sound sources at arbitrary positions having arbitrary directivities. The approach is based on the description of the directional properties of a source by a set of circular harmonics. Consequences of truncation of the circular harmonics expansion and spatial sampling as occurring in typical installations of HOA systems due to the employment of a finite number of loudspeakers are discussed. We illustrate our descriptions with simulated reproduction results.
Convention Paper 7243 (Purchase now)

P13-6 The Ill-Conditioning Problem in Sound Field ReconstructionFilippo Fazi, Philip Nelson, University of Southampton - Southampton, UK
A method for the analysis and reconstruction of a three dimensional sound field using an array of microphones and an array of loudspeakers is presented. The criterion used to process the microphone signals and obtain the loudspeaker signals is based on the minimization of the least-square error between the reconstructed and the original sound field. This approach requires the formulation of an inverse problem that can lead to unstable solutions due to the ill-conditioning of the propagation matrix. The concepts of generalized Fourier transform and singular value decomposition are introduced and applied to the solution of the inverse problem in order to obtain stable solutions and to provide a clear understanding of the regularization method.
Convention Paper 7244 (Purchase now)

P13-7 Analysis of Edge Boundary Conditions on Multiactuator PanelsBasilio Pueo, University of Alicante - Alicante, Spain; José Escolano, University of Jaén - Jaén, Spain; José J. López, Technical University of Valencia - Valencia, Spain; Sergio Bleda, University of Alicante - Alicante, Spain
Distributed mode loudspeakers consist of a flat panel of a light and stiff material to which a mechanical exciter is attached, creating bending waves that are then radiated as sound fields. It can be used to build arrays for wave field synthesis reproduction by using multiple exciters in a single vibrating surface. The exciter interaction with the panel, the panel material, and the panel contour clamp conditions are some of the critical points that need to be evaluated and improved. In this paper we address the edge boundary conditions influence the quality of the emitted wave field. The measures of the wave fields have been interpreted in the wavenumber domain, where the source radiation is decomposed into plane waves for arbitrary angles of incidence. Results show how the wave field is degraded when the boundary conditions are modified.
Convention Paper 7245 (Purchase now)

P13-8 Acoustics in Rock and Pop Music HallsNiels W. Adelman-Larsen, Flex Acoustics - Lyngby, Denmark; Eric Thompson, Anders C. Gade, Technical University of Denmark - Lyngby, Denmark
The existing body of literature regarding the acoustic design of concert halls has focused almost exclusively on classical music, although there are many more performances of rhythmic music, including rock and pop. Objective measurements were made of the acoustics of twenty rock music venues in Denmark and a questionnaire was used in a subjective assessment of those venues with professional rock musicians and sound engineers. Correlations between the objective and subjective results lead, among others, to a recommendation for reverberation time as a function of hall volume. Since the bass frequency sounds are typically highly amplified, they play an important role in the subjective ratings and the 63-Hz-band must be included in objective measurements and recommendations.
Convention Paper 7246 (Purchase now)

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