| 2007 January/February, Volume 55 Number 1/2 |
CONTENTS
PAPERS
Spatial Distribution of Distortion and Spectrally Shaped Quantization Noise in Digital Micro-Array Loudspeakers
Malcolm Hawksford 3
Digital loudspeakers are far more complex than a conventional digital-to-analog converter because quantization noise must be considered in a three-dimensional space. Minimizing off-axis degradations make digital loudspeakers a complex problem. An exploratory investigation of a large-scale array composed of subgroups of micro clusters illustrates the utility of including a matrix of oversampling and noise-shaping processing. Of the many possible topologies, an array with circularly and symmetrically distributed elements offers key advantages, especially when combined with spatial randomization.
ISO/IEC MPEG-4 High-Definition Scalable Advanced Audio Coding
Ralf Geiger, Rongshan Yu, Jürgen Herre, Susanto Rahardja, Sang-Wook Kim, Xiao Lin, and Markus Schmidt 27
The MPEG Audio standardization group has recently concluded its work for lossless and near lossless coding of audio signals with a scalable extension to the well-known MPEG-4 AAC perceptual coder. This work provides a basis for high-definition applications in recording studios, broadcasting, archiving, and Internet scenarios. An overview of this technology explains the general concepts, the extensions to existing standards, and the relationship between compression performance and processing complexity. By adding near lossless compression, the encoding techniques function within the constraints of a fixed-channel capacity.
ENGINEERING REPORTS
Optimal Design of Loudspeaker Systems Based on Sequential Quadratic Programming (SQP)
Mingsian R. Bai and Rong-Liang Chen 44
Miniature loudspeakers used in portable consumer electronic equipment produce inadequate output levels with acceptable amounts of nonlinear distortion. Because of the large number of design parameters, a systematic procedure is proposed to identify the optimal parameters in such loudspeakers. While there is extensive research on selecting the mechanical and electrical properties for larger loudspeakers, miniature dynamic moving-coil transducers require a unique strategy. Using the proposed optimization strategy, a simulated and empirical investigation showed superior performance compared to the conventional approach.
An Analytical Model of a Piezoelectric Unimorph Transducer with an Aluminum Cone
Jinqiu Sang and Xiaojun Qiu 55
An analytical model of an ultrasonic piezoelectric flexural transducer composed of a unimorph and aluminum cone has been simulated and experimentally evaluated. Because a unimorph transducer is based on a single piezoelectric layer and a single metallic layer, it is a simple and economic means for creating an ultrasonic transducer. A cone is then attached to serve as an acoustic amplifier and impedance transformer. Using a model based on energy analysis, the authors provide empirical results that are mostly consistent with the predicted response. However, modest discrepancies suggest the need to enhance the model with finite-element methods.
STANDARDS AND INFORMATION DOCUMENTS
AES Standards Committee News 63
AES3 digital interface; jitter measurements; MPEG Surround; constant-current line drive (CCLD) transducers; interface for digital loudspeakers; audio over IEEE 1394 high-performance serial bus; forensic audio
FEATURES
29th Conference Report, Seoul, Korea 66
Can You Really Hear It? Psychoacoustics in Action 75
13th Regional Convention, Tokyo, Call for Papers 102
123rd Convention, New York, Call for Papers 103
DEPARTMENTS
News of the Sections 81
Sound Track 86
New Products and Developments 88
Available Literature 90
Upcoming Meetings 91
Membership Information 92
Advertiser Internet Directory 95
In Memoriam 101
Sections Contacts Directory 104
AES Conventions and Conferences 112
FPO For the cover:
2007 January/February, Volume 55 Number 1/2
spine: 2007 January/February, Volume 55 Number 1/2