2005 July/August, Volume 53 Number 7/8

CONTENTS

PAPERS

High-Efficiency Low-Bl Loudspeakers
Ronald M. Aarts   579
As a critical design parameter of loudspeakers, especially at low frequencies, the force factor (Bl) determines the efficiency, impedance, sound level, temporal response, weight, and cost. High-Bl drivers have good efficiency but require large magnet systems. An alternative approach, which yields much lower cost and weight while preserving efficiency, uses low-Bl drivers. Prototype drivers with moving magnets and stationary coils were evaluated in a limited frequency range where efficiency is highest. This approach is suited to small portable loudspeakers.

Discrimination of Group Delay in Clicklike Signals Presented via Headphones and Loudspeakers
Sheila Flanagan, Brian C. J. Moore, and Michael A. Stone   593
The threshold for detecting a frequency-dependent group delay in a clicklike sound was found to be independent of the center frequency of the delay (1-4 kHz) and was about 2 ms for presentation via headphones, or via loudspeakers in a nonreverberant room, for both binaural and monaural listening. In a reverberant room, thresholds increased, especially at low frequencies. These results suggest that the nonlinear phase response of loudspeakers is unlikely to have any audible effect in typical rooms.

A Simple Hybrid Approach to the Time-Scale Modification of Speech
Don Knox, Nicholas Bailey, and Iain Stewart   612
Time-domain methods for stretching speech usually produce stuttering and roughness artifacts from mismatches at signal segment boundaries, especially with time-stretch ratios greater than 1.3. By combining time-domain and analysis-synthesis methods, a simple hybrid approach greatly reduced such artifacts at ratios greater than 1.6. Formal listening tests demonstrate an improvement in speech quality without incurring the complexity burden of full analysis-synthesis methods. The hybrid algorithm counters spectral mismatch and transient repetition.

ENGINEERING REPORTS

Directivity of Artificial and Human Speech
Teemu Halkorsaari, Markus Vaalgamaa, and Matti Karjalainen   620
Having an artificial mouth with the same radiating characteristics of real speakers provides a useful working tool for telecommunications research. Responses to three mouth simulators were compared to that of a group of test subjects in order to evaluate their similarity. More than 10 dB of difference was discovered in the two cases. The main contributors to the human radiating characteristics are mouth aperture size and effects of the upper body.

LETTERS TO THE EDITOR

Comments on "Low-DC-Resistance, Low-Frequency Loudspeaker Enclosures"
Alex de Koster   632
Author's Reply
Carlo Zuccatti   632

CORRECTIONS

Correction to "Low-DC-Resistance, Low-Frequency Loudspeaker Enclosures"
Carlo Zuccatti   632

STANDARDS AND INFORMATION DOCUMENTS

AES Standards Committee News   633
High-resolution multichannel digital interface (HRMAI); digital measurements; digital interfacing; file transfer; transfer technologies; microphones; listening tests

FEATURES

118th Convention Report, Barcelona   642
   Exhibitors   658
   Program   661
119th Convention Preview, New York   714
   Exhibit Previews   716
High-Density Optical-Disk Formats   749
High-Resolution Audio in an Age of Universal Playback   754

DEPARTMENTS

Reviews of Acoustical Patents   636
News of the Sections   756
Sound Track   762
Upcoming Meetings   763
Available Literature   763
Membership Information   765
Advertiser Internet Directory   767
In Memoriam   775
Sections Contacts Directory   777
AES Conventions and Conferences   784

FPO For the cover:

2005 July/August, Volume 53 Number 7/8

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