2003 April, Vol 51 Number 4

CONTENT

PAPERS

The Bidirectional Microphone: A Forgotten Patriarch
Ron Streicher and Wes Dooley   211
After reviewing the history and general issues of microphones and their sensitivity patterns, the authors focus on a pure bidirectional microphone. It is the most difficult to use. Specifically, its major virtue is the ability to place nulls at orientations to suppress unwanted sound pickup. All microphone patterns can be described in terms of a combination of an omnidirectional and figure-of-eight pattern. Many common sense rules are discussed to avoid accidental destruction of microphones' ribbons.

Efficient Tempo and Beat Tracking in Audio Recordings
Jean Laroche   226
Automatically measuring musical beat is useful in sound analysis, crossfade synchronization, and audio editing. A proposed off-line system works well for music that has a relatively pronounced beat, yet without creating burdensome demands on computational resources. The algorithm is based on detecting rapid changes in energy within a short-term frequency representation. This produces a more reliable approach because overall energy can mask those spectral components that govern the perception of a beat. A least-square optimization then identifies the best tempo and downbeat location.

On the Acoustic Radiation from a Loudspeaker's Cabinet
Kevin J. Bastyr and Dean E. Capone   234
Although it is well known that the walls of a loudspeaker cabinet vibrate at low frequencies, the authors determined the actual sound energy being radiated. Initially, a vibrometer was used to measure the surface velocity along the surface, and then a boundary-element method was used to model the acoustic radiation. By applying this method to production loudspeakers, changes in the internal bracing allow the designers to control these unwanted surface resonances, which are true radiating sources. The effects of enclosure vibration affect the overall radiation pattern of the loudspeaker and must be included in the design.

ENGINEERING REPORTS

The Virtual Loudspeaker Cabinet
J. R. Wright   244
The effective volume of a loudspeaker cabinet can be enlarged by as much as a factor of 3 if activated carbon is included inside the enclosure. The acoustic compliance, the ratio of change in volume with increased pressure, increases because the carbon absorbs and desorbs air. While it is still not commercially viable, the author demonstrates a successful laboratory model, which was judged to sound like a larger cabinet. Special care is needed to ensure that the carbon is uniformly distributed and that it does not absorb water.

LETTERS TO THE EDITOR

Comments on "Dipole Loudspeaker Response in Listening Rooms" and "Perception of Reverberation Time in Small Listening Rooms"
Tomas Salava   248
Author's Reply   James M. Kates   250
Author's Reply   W. J. Davies   251
Comments on "President's Message"
David Lloyd ben Yaacov Yehuda Klepper   251
Author's Reply   Kees A. S. Immink   251

STANDARDS AND INFORMATION DOCUMENTS

AES Standards Committee News   253
Plane-wave tubes; MAD; acoustics and sound-source modeling; microphone measurement and characterization; listening tests

FEATURES

24th Conference Preview, Banff   258
     Calendar   260
     Program   262
     Registration Form   271
MIDI and Musical Instrument Control   272
Game Audio: Follow-up to Workshop at 113th Convention   277

DEPARTMENTS

Review of Acoustical Patents   256
News of the Sections   279
Upcoming Meetings   285
Sound Track   286
New Products and Developments   287
Advertiser Internet Directory   288
Membership Information   289
In Memoriam   290
AES Special Publications   293
Sections Contacts Directory   298
AES Conventions and Conferences   304

FPO For the cover:

2003 April, Vol 51 Number 4

spine: 2003 April, Vol 51 Number 4