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Don Keele on Constant Beam Transducer (CBT) Speakers and then some

amirm

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Don is one of those very down to earth people that is lovely to listen to, pun intended :). He was the one that discovered navy research for sonars in building transducers with unified patterns and applied it home and commercial speaker systems. CBT as it is called, has incredible benefits which he explains yet they are deceptively simple to build. It is one of those "cheat the laws" of physics kind of things.

Even though this presentation is about CBTs, he contrasts them frequently with how traditional speakers work including some really nice animations. Unfortunately everything is in short-hand so you may have to pay close attention. Topics covered are speaker lobing, effects of floor reflections, line arrays (what they are and aren't), horns, directivity, etc.

The videos are all HTML 5 so you can speed them up (I suggest doing that for the first video):

 
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Kevin Keele

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May 10, 2016 Don and Kevin Keele have released "The CBT Chronicles" on 'The Official D.B. Keele, Jr. Youtube page'. The CBT Chronicles are a nine-part video series by inventor Don Keele covering the history and technology of CBT (Constant Beamwidth Transducer) loudspeaker arrays including detailed comparative measurements of a traditional speaker system and a CBT array. You can access the playlist at: http://tinyurl.com/CBTChronicles (redirecting to Youtube)
For further information contact Don Keele at [email protected]



Published on May 9, 2016
The CBT Chronicles are a nine-part video series by inventor Don Keele covering the history and technology of CBT (Constant Beamwidth Transducer) loudspeaker arrays including detailed comparative measurements of a traditional speaker system and a CBT array. The first five parts of the nine-part CBT Chronicles are devoted to an introduction to CBT arrays covering the general background and history of CBT arrays. The last four parts of the Chronicles cover a series of real-time measurements comparing the coverage of a traditional well-designed three-way system with a two-way CBT array system both measured over a reflective ground-plane (a tile floor).

These videos are not a Power Point production but an extemporaneous and unrehearsed lecture by Don Keele with real (cheesy) props and actual loudspeakers.

Part 1 of 9: Introduction: CBT Background & History

This first part of this introduction goes into brief detail about CBT technology including its military roots, associated patents, Don Keele’s background and technical papers, and where the video series was produced.

Watch the full CBT Chronicles Here
https://www.youtube.com/playlist?list...

Reference Links

Church Production Magazine: CASE-STUDY: Self-Installation in the Extreme:
http://www.churchproduction.com/story...

JBL Pro Series of CBT Line Array Columns with “Constant Beamwidth Technology”
http://www.jblpro.com/www/products/in...

U.S. Navy Acoustical Society CBT Papers, ZIP Download Link:
http://tinyurl.com/NavyCBT

Keele Patent List
https://www.google.com/?tbm=pts&gws_r...

Don Keele Scientific and Technical Academy Award:
https://www.oscars.org/sci-tech/cerem...

The Official D.B. Keele Website
http://www.dbkeele.com
 
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AJ Soundfield

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I'd love to know how the do (did?) in Harmans blind tests vs the Salon 2, which is referenced in the CBT paper.
I've heard both on several occasions, sighted of course.
 

TBone

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welcome, enjoyed the videos, esp 4/6.
 

DonH56

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This is cool, I had forgotten about these after reading about them a few years ago.

My introduction to D.B. Keele was actually for sonar, years ago... He is mentioned in if not an author of one of my acoustics texts.
 

Cosmik

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I love this sort of thing - thanks for the links.

How does it sound? I saw one comment referring to a demo at a show that said "They don't image like monitors". Is this actually the case? If so, which is the more 'correct' - the CBT or the monitor?
 

Archaea

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I love this sort of thing - thanks for the links.

How does it sound? I saw one comment referring to a demo at a show that said "They don't image like monitors". Is this actually the case? If so, which is the more 'correct' - the CBT or the monitor?

It sounds very different to monitors. The sound doesn’t seem to originate from anywhere. You might say there is no extremely focused sweet spot like traditional monitors, instead — everywhere is a “less focused” giant sweet spot. Its a very unique room filling sound!

I experienced hearing a CBT design Don helped design at Axpona 2017 when Don Keele, in person, helped introduce the Epique CBT24K speaker in partnership with Parts-Express. In an open area of the giant hotel hallway of the trade show floor I walked by a mammoth pile of Parts-Express speakers (various products they carried) with the CBT24K out front stand alone. As I walked by the display the sound was like a uniform wall, it sounded the same no matter where I walked within like an 18' range. I couldn't' tell where it sourced from. It wasn't directional and barely changed volume as you walked closer or further away? It was “weird” and novel! My friend I was with asked me if it the line arrays playing, since he spotted and recognized Don Keele, and understood the CBT technology more than me. I told him no - it didn't sound like those little line array speakers with the tiny drivers could be doing that. I proceeded to walk up to the mountain of speakers and start putting my ear next the drivers trying to figure out what speaker was producing such a uniform sound regardless of where you were??? We’re all the speakers on I initially wondered??? I came to the realization it WAS that little line array pair with tiny drivers. I was blown away. My buddy and I each bought a pair right there at the trade show floor. Sadly I never got around to putting mine together. Life happens - it's still unfinished, and in the meantime I bought 13 JBL CBT 70j-1line array speakers for my HT room so there isn’t a whole lot of motivation, but someday I’ll get back to them. I plan to finish them nicely (started, but stalled out) and then put them in our living room.

These are the ones I bought at the show:
195865_upload_2019-2-20_14-59-29.png


https://www.parts-express.com/epique-cbt24k-line-array-speaker-kit-pair--301-984

They have a big brother called the CBT36K
https://www.parts-express.com/cbt36k-line-array-speaker-pair-kit--301-980

The story on the JBL CBTs I’m now using in my HT is here:
https://www.audiosciencereview.com/...eakers-in-commercial-project.310/#post-435727
 
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