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Journal of the Audio Engineering Society

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2003 October - Volume 51 Number 10

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Papers

Advances in Low Bit-Rate Audio Coding: A Digest of Selected Papers from Recent AES Conventions

Authors: Chiang, Wei-Hwa; Hwang, Chingtsung; Hsu, Yenkun

[feature article] Low bit-rate audio coding has been part of mainstream audio engineering for a considerable number of years now, but new developments continue to arise and improvements continue to be made. The challenges of addressing scalable delivery for networked and mobile applications are considerable, as are those associated with narrow-band broadcasting applications such as DRM (Digital Radio Mondiale). There are also ways in which perceived sound quality can be improved using novel techniques such as SBR (spectral band replication) while maintaining remarkably low bit rates. In this article selected papers from recent AES conventions are reviewed to provide an overview of some of the key developments in these and other areas.

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Acoustical Renovation of Tainan Municipal Cultural Center Auditorium

Authors: Chiang, Wei-Hwa; Hwang, Chingtsung; Hsu, Yenkun

An acoustical analysis was conducted for renovating the auditorium in the Tainan Municipal Cultural Center for orchestral programs. Design strategies included using more reflective surfaces, incorporating the pit as part of the platform, installing suspended reflectors, and splaying the rear sidewalls. The unoccupied midfrequency reverberation time and the strength factor were increased to 2.02 s and 4.6 dB, respectively. The overall impression rating was 5.3 on a 7-point scale.

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Wavefront Sculpture Technology

Authors: Urban, Marcel; Heil, Christian; Bauman, Paul

OPEN ACCESS

The Fresnel approach in optics is introduced to the field of acoustics. Fresnel analysis provides an effective, intuitive way of understanding complex interference phenomena and allows for the definition of criteria required to couple discrete sound sources effectively and to achieve coverage of a given audience geometry in sound-reinforcement applications. The derived criteria form the basis of what is termed Wavefront Sculpture Technology.

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Sensitivity of High-Order Loudspeaker Crossover Networks with All-Pass Response

Authors: Cochenour, Brandon; Chai, Carlos; Rich, David A.

The sensitivity of high-order filter networks to component matching tolerances increases with the filter order. For the crossover network of an audio loudspeaker that is designed to sum to an all-pass network, it is demonstrated that the sensitivity to component matching tolerances may be dwarfed by sensitivities to other effects. Second- to eighth-order Linkwitz/Riley crossovers are examined. The analysis also subsumes networks with transmission zeros and optimized networks where the effects of frequency-response errors introduced by the respective driver transfer functions are minimized. Crossover networks are considered which are least sensitive to the combined effects of component tolerances, pathdelay effects, interaction of filter sections in loudspeakers that divide the incoming signal into three or more subbands, and driver transfer functions.

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Two-Port Representation of the Connection between Horn Driver and Horn

Authors: Behler, Gottfried K.; Makarski, Michael

A method for measuring and describing horn drivers and horns as independent parts was investigated. It is shown that the well-known two-port representation can be adopted for system characterization considering certain assumptions and limitations. The horn driver is represented as a two-port whereas the horn is characterized by its acoustical input impedance and, due to its three-dimensional sound radiation, by its on-axis transfer function and a relative directivity. With both sets of parameters the electrical input impedance, the transfer function, and the directivity of any horn driver/horn combination can be synthesized by a software tool without a need for measuring the real combination. This method speeds up procedures of either loudspeaker system design or the design and optimization of new horn drivers and horns, respectively. Besides the general-purpose measuring techniques, some specialized measuring equipment is required such as an impedance tube fitted to the horn throat and an anechoic chamber to record the directivity of the horn. Finally, all possible combinations of seven horn drivers and eleven horns have been studied to show the reliability of the method.

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