Meeting Announcement – July with Don Keele at Farm Fresh Studios

The Central Indiana Section of the Audio Engineering Society is pleased to announce our July meeting, to be held Thursday July 18, 2013 featuring Don Keele speaking on the topic of “Introduction to CBT Loudspeaker Arrays.”

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.

We have invited percussionist John Marque ( to participate in a live-versus-recorded drum-kit shootout with the pair of CBT36 systems.

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.

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.

The meeting will be held July 18, 2013 at 7:30pm in Farm Fresh Studios To ensure an accurate count for the meeting, please RSVP .


Meeting Information

Date: July 18, 2013 at 7:30pm
Location: Farm Fresh Studios
2115 N Mount Gilead Rd
Bloomington, IN  47408 (map)

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