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Is anyone thinking about Don Keele's CBT Arrays?

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  • Is anyone thinking about Don Keele's CBT Arrays?

    Though the demo was brief..I was stunned ..I've never heard that sort of sound pressure and clarity from a speaker before.Are there plans from which to build these somewhere?

  • #2
    Re: Is anyone thinking about Don Keele's CBT Arrays?

    Originally posted by fred lewis View Post
    Though the demo was brief..I was stunned ..I've never heard that sort of sound pressure and clarity from a speaker before.Are there plans from which to build these somewhere?
    That's in the works. I've been discussing it with Marshall Kay and Don Keele.

    Comment


    • #3
      Re: Is anyone thinking about Don Keele's CBT Arrays?

      Fred,

      I was at the show too, and was impressed by the demonstrations I saw. However, what struck me most about the CBT array wasn't its output levels, but its consistency throughout the listening area and through multiple horizontal planes (that is, the sound didn't change when I stood up or sat down). However, I think that for most home listening rooms, a nearfield line array should be able to produce that same consistency in multiple horizontal planes, because the array could be built to extend from floor to ceiling. The CBT has its best application where a certain vertical coverage angle is required, and building an array from floor to ceiling is impractical (either due to a high ceiling or no ceiling). However, if you can build a nearfield line array that goes completely from floor to ceiling, you'd produce a line source that sonically seems to extend infinitely in either direction (due to the floor and ceiling reflections effectively extending the array), and you'd achieve consistent flat response in all horizontal planes from floor to ceiling. But if you only listen in one plane, a point source is still the best option because of its superior impulse response when compared to any type of array, and even better if some directivity control is at work to provide a seamless transition in power response from the woofer to the tweeter (such as designs by SP Technology, NuForce, Amphion, and Aurelia which incorporate HF waveguides).

      One shortcoming of the CBT arrays as Keele demonstrated was the required "Legendre Shading" (amplitude-shading of some of the drivers) which effectively decreases the output of the drivers in the upper, swept-back part of the CBT array. This would result in some drivers of the array reaching their mechanical limits before the others; in the arrays demonstrated with the ND90, the lower ND90s were beginning to produce audible noise from the turbulent air flow through their motors and small leaks in the box began to whistle while the upper drivers were loafing along comfortably. Every design has a tradeoff. However, an inductor wired in parallel with the shading resistor could allow the upper drivers to roll back in at the baffle step frequency and combat baffle step effects. Without the subwoofer, the arrays actually seemed to lack bass punch (I found them a little too polite in the 'slam' department), though they were well behaved, and they did sound very nice with the subwoofer deactivated. A line array would require less baffle step correction than a point-source enclosure, because the array wouldn't lose directivity in the vertical plane, so it would only become omnidirectional in a single plane, so only about 3 dB of baffle step would be needed instead of the usual 6 in a free field environment, and even less than that in a room. Also, Keele's arrays as-demonstrated didn't seem to give any attention to controlled directivity in the horizontal plane. The drivers used to form each line were small enough to radiate throughout 180 degrees -3dB up to about 7kHz and -6dB to 13 kHz. However, in long and narrow rooms where line arrays are most optimally applied in live sound, this wouldn't be advantageous -- it would create a significant side-wall reflection problem.

      The CBT array is undoubtedly Keele's landmark achievement, but there are a couple of practical concerns that would need some attention in a commercial product. For live sound, where horizontal pattern control is needed, I personally think much of what the CBT achieves is already achieved elegantly by Tom Danley's Shaded Amplitude Lens (the "Genesis Horn" project), and the Shaded Amplitude Lens could also be applied to performing the amplitude shading that makes the CBT array work.

      To counterbalance my minor criticisms of the particular implementation of CBT technology that was displayed at the event, I personally felt it was great to have Don's support at the event as a guest judge. I felt it showed that professional audio engineers have at least some respect and appreciation for what us hacks are trying to do. Talking with Don after the event, I learned that much of the CBT concept development wasn't done with rivers of R&D cash, but through favors from friends. It personally encouraged me to try to push the envelope.
      Best Regards,

      Rory Buszka

      Taterworks Audio

      "The work of the individual still remains the spark which moves mankind ahead, even more than teamwork." - Igor I. Sikorsky

      If it works, but you don't know why it works, then you haven't done any engineering.

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      • #4
        Re: Is anyone thinking about Don Keele's CBT Arrays?

        They were cool.
        18hz is scary.

        Comment


        • #5
          Re: Is anyone thinking about Don Keele's CBT Arrays?

          http://www.jblpro.com/catalog/suppor...1460&doctype=3

          http://www.jblproservice.com/pdf/CBT/CBT%2050LA-WH.pdf

          Comment


          • #6
            Re: Is anyone thinking about Don Keele's CBT Arrays?

            Cannot display/download the first document? any alternative. Thanks.

            Comment


            • #7
              Re: Is anyone thinking about Don Keele's CBT Arrays?

              Originally posted by ttan98 View Post
              Cannot display/download the first document? any alternative. Thanks.
              Working fine now here.
              http://www.nytimes.com/2010/10/14/bu...html?src=busln

              http://mixonline.com/mag/audio_new_york_metro_46/

              Comment


              • #8
                Re: Is anyone thinking about Don Keele's CBT Arrays?

                Go to JBL Pro.com, click "Downloads," then "Technical Notes." Scroll down to Vol. 1 #35, "CBT."

                Comment


                • #9
                  Re: Is anyone thinking about Don Keele's CBT Arrays?

                  Hi,

                  Thanks fellows, it didn't on my Chrome V5, but works on MS explorer.

                  Comment


                  • #10
                    Re: Is anyone thinking about Don Keele's CBT Arrays?

                    The Novak article reference (from the JBL article above) is now on line (it used to be available only through the AES for a fee).

                    http://www.ee.ic.ac.uk/naylor/LineSo...rs/novak62.pdf

                    I have a pair of the Jensen CalStar 1010 described, from the early 60's, rescued several years ago from a then-soon-to-be-demolished restaurant . . . the drivers are not in the best of shape, but the directionality is (more or less) as advertised. I've contemplated replacing the drivers with some closeouts and re-working the delay networks, but will probably (if I ever get around to it) just build new lines.

                    Not much "new" under the (audio) Sun . . . CBT is at least 50 years old . . .
                    "It suggests that there is something that is happening in the real system that is not quite captured in the models."

                    Comment


                    • #11
                      Re: Is anyone thinking about Don Keele's CBT Arrays?

                      Referring to the JBL paper Zilch provided a link for, "CBT, Constant Beamwidth Technology," can PCD help design CBT arrays? I mean working out the passive ladder delays for virtual curves, driver spacing, etc.? And how about the 5 way constant beamwidth array in fig. 15?

                      Curious as to what software designers use to design this sort of line array.
                      http://www.nytimes.com/2010/10/14/bu...html?src=busln

                      http://mixonline.com/mag/audio_new_york_metro_46/

                      Comment


                      • #12
                        Re: Is anyone thinking about Don Keele's CBT Arrays?

                        I'm looking for 2" full-rangers to build the little guy.

                        There WAS a $2.00 buyout that would have worked:

                        http://www.parts-express.com/pe/show...number=289-124

                        Comment


                        • #13
                          Re: Is anyone thinking about Don Keele's CBT Arrays?

                          Pardon the line array ignorance...but what happens above 14kHz with a full ranger like that? The JBL paper states the LF from the multiple drivers combine to compensate for roll off, but that does not happen for the HF.

                          This would be a good build maybe to flank an apt. dwellers flat panel TV, with appropriate angle down to the couch, if required. Of course, add a sub.

                          Virtual curve, right? I might be in on the build.
                          http://www.nytimes.com/2010/10/14/bu...html?src=busln

                          http://mixonline.com/mag/audio_new_york_metro_46/

                          Comment


                          • #14
                            Re: Is anyone thinking about Don Keele's CBT Arrays?

                            No clue 'til we build, which means find a suitable driver.

                            Cool thing is using group delay to steer the array.

                            [These guys are smarter than your ordinary Zilchster.... :D ]

                            Comment


                            • #15
                              Re: Is anyone thinking about Don Keele's CBT Arrays?

                              Madisound has a couple of 2-3" drivers for sale: https://www.madisound.com/store/specials.php

                              Here's their regular selection of 2" FR drivers: https://www.madisound.com/store/inde...ath=45_241_283
                              "He who fights with monsters should look to it that he himself does not become a monster. And when you gaze long into an abyss the abyss also gazes into you." Friedrich Nietzsche

                              http://www.diy-ny.com/

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