2007 June, Volume 55 Number 6

CONTENTS

PAPERS

Dynamic Measurement of Loudspeaker Suspension Parts
Wolfgang Klippel   443
Being a complex device made of many independent elements, a loudspeaker is both a system and a combination of individual elements. For example, the restoring property of the suspension seldom achieves the linearity of an ideal spring. A laboratory technique is proposed that allows the nonlinear properties of a suspension to be measured and analyzed in a mechanical-acoustical environment that mimics a real loudspeaker but without being influenced by other elements. The pneumatic excitation of the suspension allows for dynamic measurements while vibrating at the lower limit of the audio band.

On the Stability of Time-Varying Recursive Filters
Jean Laroche   460
Conventional mathematics used to describe recursive filters are no longer valid when their coefficients are time varying. A new approach is required to determine stability. Better insight into the causes of instability can be gained by using a state-space representation of the filter, and an analysis shows that some filter topologies are better suited to time-varying coefficients than others. Several techniques, based on estimating the average value of the effective switch-time gain, are presented for stabilizing an otherwise unstable time-varying filter.

ENGINEERING REPORTS

Direct Acoustic Digital-to-Analog Conversion with Digital Transducer Array Loudspeakers
Jorge Mendoza-López, Simon C. Busbridge, and Peter A. Fryer   472
A research study of a digital loudspeaker composed of an array of transducers explores the requirements for achieving quality sound. Three configurations were tested by both simulation and with empirical prototypes. Key factors, such as transducer mismatch, array size, transducer spacing, baffle diffraction, and configuration, were isolated and quantified. Although harmonic distortion exceeds the theoretic base level, a smooth rolloff in transducer bandwidth improved performance. Path length differences between transducers and the listener are minimized with smaller configurations.

Spatial Sound Reproduction with Directional Audio Coding
Ville Pulkki   503
A proposed signal processing method reproduces the spatial properties of sound recordings made with existing microphones. In the analysis section, sound direction and diffuseness are estimated in time and frequency. In the synthesis section, diffuse and nondiffuse parts of each frequency band are reproduced using different strategies, which circumvents some artifacts in traditional reproduction methods. Spatial attributes can be encoded as metadata for transmission along with one or more audio channels. In addition to high-quality sound reproduction, the technique can also be applied to teleconferencing. Both a mathematical analysis and informal listening tests validate the approach.

LETTERS TO THE EDITOR

Comments on "Multiband Audio Processing and Its Influence on the Coverage Area of FM Stereo Transmission"
Scott Dorsey   517
Author's Reply
Oscar Bonello   517

FEATURES

30th Conference Report, Saariselkä, Finland   518
32nd Conference Preview, Hillerød, Denmark   528
     Calendar   530
     Program   531
     Registration Form   536
Spatial Audio   537

DEPARTMENTS

News of the Sections   543
Upcoming Meetings   547
Sound Track   548
New Products and Developments   549
Available Literature   550
Membership Information   553
Advertiser Internet Directory   555
In Memoriam   558
Sections Contacts Directory   560
AES Conventions and Conferences   568

FPO For the cover:

2007 June, Volume 55 Number 6

spine: 2007 June, Volume 55 Number 6