An improved statistical-acoustics model of high-frequency sound fields in coupled rooms is developed by incorporating into prior models geometrical-acoustics corrections for both energy decay within subrooms and energy transfer between subrooms. The conditions under which statistical-acoustics models of coupled rooms are valid approximations to geometrical acoustics are examined by comparison of computational geometrical-acoustics predictions of decay curves in two- and three-room systems with those of both improved and prior statistical-acoustics models. The accuracy of the decay model used within subrooms is found to have a primary influence on the accuracy of predictions in coupled systems. Likewise, nondiffuse transfer of energy is shown to significantly affect decay of energy in systems of coupled rooms. The decrease in energy density of the reverberant field with distance from the source, which is predicted by geometrical acoustics, is found to result in spatial dependence of decay-curve shape for certain coupling geometries. Geometrical effects are shown to contribute to the failure of statistical-acoustics models in the case of strong coupling between subrooms; thus, previously proposed statistical-acoustics criteria cannot predict the point at which the models break down with consistent accuracy.
Inaccuracies in computation and auralization of room impulse responses are related in part to inadequate modeling of edge diffraction, i.e., the scattering from edges of finite surfaces. A validated time-domain model (based on analytical extensions to the Biot-Tolstoy-Medwin technique) is thus employed here to compute early room impulse responses with edge diffraction. Furthermore, the computations are extended to include combinations of specular and diffracted paths in the example problem of a stage-house. These combinations constitute a significant component of the total nonspecular scattering and also help to identify edge diffraction in measured impulse responses. The computed impulse responses are then convolved with anechoic signals with a variety of time-frequency characteristics. Initial listening tests with varying orders and combinations of diffraction suggest that (1) depending on the input signal, the diffraction contributions can be clearly audible even in nonshadow zones for this conservative open geometry and (2) second-order diffraction to nonshadowed receivers can often be neglected. Finally, a practical implementation for binaural simulation is proposed, based on the singular behavior of edge diffraction along the least-time path for a given source-edge-receiver orientation. This study thus provides a first major step toward computing edge diffraction for more accurate room acoustics auralization.
The ability of computational geometrical acoustics to accurately model energy decay in systems of coupled rooms is investigated both theoretically and experimentally. Unlike single-volume rooms, coupled rooms have reflection density that is not described by a single quadratic function of time. It is shown that tail-correction procedures used by beam-axis-tracing algorithms, which assume quadratic growth of reflection density, can lead to inaccurate predictions in coupled rooms. Further, beam-axis tracing implemented as ray tracing with a growing detection sphere is susceptible to error in coupled rooms when the detection sphere extends into adjacent subrooms. Marked error is anticipated in those cases for which the source and receiver are in the less reverberant of two rooms and is expected to be most severe for ͑1͒ small coupling apertures and ͑2͒ receiver positions near boundaries between subrooms. Errors are demonstrated by comparison of computational geometrical acoustics predictions with scale-model measurements made in a two-room coupled system. A revised beam-axis/ray-tracing algorithm is investigated that circumvents possible error mechanisms by switching to ray tracing for the late part of the decay. Comparisons with scale-model measurements indicate that the revised algorithm is able to predict energy decay accurately in coupled rooms.
This much needed book on the acoustics of worship spaces has been produced by three widely-experienced authors and is worthy of consideration by architects, acousticians, builders, administrators and anyone interested in the history or construction of spaces for worship.The book has two parts. Part one gives a cursory review of the fundamentals of acoustics and its measurement, followed by properties of hearing, sound absorbing materials, planning for good acoustics in worship spaces, and means for achieving quiet. The section on "sound systems for clarity and reverberation" is excellent and should be read by every acoustician.Part two deals with the history of Judaism, Christianity and Islam. It goes into details of the construction of synagogues, churches and mosques through the ages, but particularly as they exist today.Important design considerations include: floor plans and sections, desirable reverberation times for music and for speech intelligibility, location of pipe organs and choirs, and means for controlling noise. The section on sound systems deals with the various ways of achieving speech intelligibility in spaces of widely different shapes, reverberance, and seating arrangements. The different types of systems considered are: a) central, b) distributed cone, c) distributed pew back, d) distributed directional horns, e) distributed delayed columns, and f) horizontal line sources. Detailed equipment information is given on microphones, control centers, direct radiator loudspeakers, directional horns, and distributed digital-signal processing. A useful section is included on the specification of sound systems, choosing types of equipment, installation techniques, tests, and service requirements.In dealing with worship spaces, it appears that synagogues pretty much all emphasize speech intelligibility (and so do Mosques). Spaces for Christianity cover a wide range from cathedrals, to mega-churches, to village churches. The spoken and musical characteristics for this range are translated into means for providing beautiful acoustics for organ music and uniform speech intelligibility. Loudspeakers are often everywhere and merging them into the architecture is usually a major consideration,The book ends with an appendix that gives references and notes to the text and acknowledgments.
Effects of aperture diffraction on reverberant energy decay in coupled-room auditoria are estimated at mid frequencies, defined as frequencies above the Schroeder frequencies of subrooms, but having wavelengths of the order of the characteristic dimensions of apertures. Hybrid models are developed that account for wave effects at apertures but treat sound fields in subrooms using high-frequency models. The models give more accurate estimates of the randomincidence power transmission coefficient. These estimates agree well with independent measurements of circular apertures in thin, hard screens. When used to predict the effects of 1 This paper is an expanded version of "Midfrequency modeling of coupled-room performance spaces by computation of transmission coefficients of apertures and arrays of apertures," which was presented at the
No concert hall has a perfectly diffuse field, although many are close enough that their decay is perceived as linear. In recent years, concert hall acousticians have taken steps to ensure more exaggerated double-sloped (nonlinear) decays in their concert halls by using coupled volumes. Some acousticians feel that a coupled volume gives a hall a balance between clarity (subjectively speaking) and reverberance. However, there have been no studies done to determine when a nonlinear decay becomes perceptibly different from a linear decay. This work seeks to identify the threshold of perception for nonlinear decays. Nonlinear impulse responses of different lengths are generated by first computing uncoupled impulse responses of a concert hall and a coupled volume in CATT-Acoustic. The two linear impulse responses are convolved in matlab. These convolved impulse responses are manipulated to systematically vary the degree of nonlinear decay. The various nonlinear impulse responses are then convolved with anechoic signals with different temporal characteristics and presented to listeners for evaluation. From these evaluations, a criteria is derived to determine when a nonlinear decay becomes audibly different from a linear decay to a listener for various representative signals.
This investigation determines the audibility of edge-diffraction when used in auralization of a stage house. Computed impulse responses with varying orders of diffraction are auralized and compared via listening tests. These impulse responses are also compared with measured, auralized impulse responses from a scale model. Results indicate that, for the positions studied, first-order diffraction is significantly more audible than second-order diffraction. Thus, higher-order edge diffraction calculations can possibly be neglected in auralization programs.
Although much research has focused on determining optimal acoustical environments for students in classrooms, relatively little has addressed the classroom as an acoustical workspace for teachers, who may suffer from stress and vocal strain due in part to poor acoustical environments. Although the primary problem is typically the background noise level (whether due to ventilation or students), it is also interesting to study systematically how controlling early reflections may improve the audible ‘‘room response’’ at the teacher’s speaking location without inordinately increasing the reverberant level of the background noise. Moreover, the room response at the talker’s position may help reduce the perceived need to strain the voice, as long as the reflections are not so delayed as to be disturbing. In this study approximately ten configurations of absorptive and reflective surfaces in a ‘‘typical-sized’’ classroom are auralized in real time. For each room condition, subjects rate the ‘‘talker comfort’’ in terms of perceived loudness of their speech, possible disturbance from echoes or increased background noise, and other factors. The primary descriptive physical parameter is essentially the relative amplitude and delay of clusters of early reflections, which are not always well characterized by the classical room-acoustics descriptors. Initial results of the modeling and subject testing will be presented.
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