Audio Engineering Society
Chicago Section
Meeting Recap - April 23, 2013
AES
Chicago Section Meeting Notice
Meeting Date: April
23,
2013
TOPIC:
Introduction
to CBT Loudspeaker Arrays
PRESENTER:
Don
Keele of Audio
Artistry
LOCATION:
Shure
Incorporated
5800 W. Touhy Ave, Niles, IL 60714 -
Directions below
ABOUT
THE PRESENTATION:
Come
out and hear Don Keele talk about his loudspeaker line arrays
based on CBT technology. He has been an ardent advocate and
evangelist for the concepts for over ten years and believes the
CBT know-how can vastly improve the sound field uniformity of
existing line arrays and conventional loudspeaker systems. Don
will discuss the background and history of CBT arrays and will
describe and discuss the measurement and simulation results of
several CBT line arrays including the Audio Artistry CBT36
high-end home loudspeaker which is sold in an inexpensive DIY kit
form by Parts Express and finished form by Audio Artistry. The
CBT36 system will be setup for listening.
CBT, which stands for “Constant Beamwidth Transducer,” is a term originated by the U.S. military in a series of three un-classified Naval Research Lab ASA papers published in the late 70s and early 80s. These papers describe spherical-cap underwater transducers with special frequency-independent “Legendre” shading that provide extremely-uniform broadband coverage without the need for any special or complex signal processing. Don applied the technology to loudspeaker arrays in a series of six AES papers between 2000 and 2010 and some of the technology is now in the public domain. The CBT arrays provide a broadband constant-directivity 3D sound field that is incredibly uniform and well behaved with frequency at all distances from very close to far away. The vertical beamwidth control and coverage of the CBT line arrays often exceeds even the finest constant-directivity pro horns.
The CBT line-array concept dictates that multiple loudspeakers be placed evenly around a circular arc and that frequency-independent shading (simple changes in level) be applied to each speaker. An alternate, but much more complex, CBT implementation method is based on the use of delays to provide the circular curvature of a straight-line array. Circular-arc CBT arrays can be implemented passively and do not require any sophisticated DSP signal processing except for simple level changes. CBT array possibilities extend over the full loudspeaker product range from professional, commercial, consumer, home theater, computer, and multimedia. Note that Harman/JBL has copyrighted the term “CBT” in the loudspeaker industry where it stands for “Constant Beamwidth Technology” and has three patents issued to Keele on some of the CBT concepts
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ABOUT
THIS MONTH’S SPEAKER:
D.B.
(Don) Keele, Jr. has worked for several companies in the area of
loudspeaker R&D and measurement technology including
Electro-Voice, Klipsch, JBL, Crown, and Harman International. He
holds eight patents with topics including "constant-directivity"
loudspeaker horns, loudspeaker arrays, and signal processing. He
is a fellow of AES. For ten years he wrote for Audio Magazine as a
Senior Editor performing loudspeaker reviews. More recently, he
worked for Harman/Becker Automotive Systems in the advanced
technology development group and was a member of the Harman
corporate acoustics engineering group working under Floyd Toole.
Currently he heads his own consulting company DBK Associates and
Labs and recently joined loudspeaker manufacturer Audio Artistry
as VP of R&D. His passion for the last eleven years has been
to promote the use of CBT (Constant Beamwidth Transducer)
loudspeaker technology in the loudspeaker industry.
Mr. Keele holds two BS degrees in EE and Physics from California State Polytechnic University and an MSEE degree from Brigham Young University where he minored in acoustics. He has presented and published over 40 technical papers on loudspeaker design and measurement methods and other related topics, among them the paper for which he won the AES Publication Award, "Low-Frequency Loudspeaker Assessment by Nearfield Sound-Pressure Measurement". He is a frequent speaker at AES section meetings and workshops, has chaired several AES technical paper sessions, and is a past member of the AES review board. Mr. Keele is a past member of the AES Board of Governors and is past Vice President, Central Region USA/Canada of the AES. Mr. Keele received the TEF Richard C. Heyser Award in 2001. In 2002, he received a Scientific and Engineering Academy Award from the Academy of Motion Picture Arts and Sciences for work he did on cinema constant-directivity loudspeakers. In 2011 he received the ALMA Beryllium Lifetime Achievement Award for contributions to the loudspeaker industry.
