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Audio
Engineering Society
Chicago SectionMeeting 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
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.
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