| 2008 November, Volume 56 Number 11 |
CONTENTS
PAPERS
Controlled Acoustic Bass System (CABS) A Method to Achieve Uniform Sound Field Distribution at Low Frequencies in Rectangular Rooms
Adrian Celestinos and Sofus Birkedal Nielsen 915
A new method for improving the low-frequency response in small- and medium-sized rooms uses a pair of front loudspeakers for initiating a traveling plane wave and a canceling rear pair of loudspeakers that effectively remove the acoustic reflection of the back wall. The rear loudspeakers receive a delayed and opposite phase version of the signal presented to the front loudspeakers, thereby canceling the plane wave when it reaches the rear of the room. Unlike equalization techniques that emphasize a single sweet spot, this approach covers the entire room. The upper frequency limit of the system is higher for smaller rooms. Based on an evaluation in two rooms, the system works as intended. Using this method, listeners experience a clear bass sound image, and the rear loudspeakers are inaudible.
MPEG Surround-The ISO/MPEG Standard for Efficient and Compatible Multichannel Audio Coding
Jürgen Herre, Kristofer Kjörling, Jeroen Breebaart, Christof Faller, Sascha Disch, Heiko Purnhagen, Jeroen Koppens, Johannes Hilpert, Jonas Rödén, Werner Oomen, Karsten Linzmeier, and Kok Seng Chong 932
Finalized in 2006, the MPEG Surround specification enables the transmission of multichannel audio signals at data rates close to those of one- and two-channel systems. This paper describes the technical architecture and capabilities of the specification. Verification tests include several operational modes as they would be used in typical application scenarios. In order to achieve backward compatibility with legacy devices that are not compliant with MPEG Surround, the spatial side information is embedded in either an ancillary part of the downmix bit stream or in a separate stream. This approach is vastly superior to a matrixed system at the comparable data rates.
Modeling the Transient Acoustic Field Radiated by a Loudspeaker
D. J. Chappell, G. Geaves, D. J. Henwood, P. J. Harris, and R. Chakrabarti 956
This research concentrates on determining the transient acoustic field of a loudspeaker by applying uncoupled finite-element and boundary-element methods. The well-known problem of instability when working in the time domain was avoided by using a Burton–Miller type integral equation formulation. The accuracy of the results shows that this approach is well suited for modeling loudspeakers. Stable results were obtained in all cases and they were reasonably accurate when the time step was smaller than or equal to the experimental sampling rate. Two examples of insights are provided: differing decay rates of various loudspeaker components, and the presence of the acoustic center.
Some Observations on Sensitivity to HRTF Magnitude
Pablo F. Hoffmann and Henrik Møller 972
The required number of head-related transfer functions (HRTFs) is determined by audible differences in the spectral characteristics as a function of separation angle. The experiment tested the ability of subjects to discriminate between changes in the minimum-phase HRTF while the interaural time difference remained constant. Subjects were able to discriminate spectral differences over a range of 3 to 17 degrees depending on the spatial locations being represented. The thresholds for detectable change in polar angle were consistently lower than changes in lateral angle. Due to the variation of the threshold, the choices of reference angles for HRTF measurements need not be uniform over the sphere.
STANDARDS AND INFORMATION DOCUMENTS
AES Standards Committee News 983
Digital audio measurements; digital input/output interfacing; audio-file transfer and exchange; audio networks; microphone measurement and characterization; storage of tape; life expectancy of CD-ROM
FEATURES
35th Conference Preview, London 988
Program 990
Concert Hall Acoustics Francis Rumsey 1001
Call for Nominations for the Board of Governors 1022
Call for Awards Nominations 1023
DEPARTMENTS
News of the Sections 1005
Upcoming Meetings 1011
New Products and Developments 1013
Available Literature 1013
Membership Information 1014
Advertiser Internet Directory 1015
Sections Contacts Directory 1024
AES Conventions and Conferences 1032
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2008 November, Volume 56 Number 11
spine: 2008 November, Volume 56 Number 11