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Jim's new CBT Arrays

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  • #16
    Another fantastic build Kevin! This is oozing with Kevin's signature attention to care for every little thing.

    Originally posted by xmax View Post
    I'm no expert on line arrays and with all due respect, seemingly with all that Sd one could be designed with ample low end,
    is there something with a line array that makes that not practical? I see subs are often recommend with them.
    There is not as much Sd as you would think. There is only 20cm^2 on each driver. With 24 of them you have 480cm^2. While that's the equivalent Sd of a 12" woofer, these 2.5" drivers only have 2.65mm of Xmax. Therefore, the displacement is only 480cm^2 x 2.65mm = 1272, which is about the same as a 8" woofer with 5.8mm of excursion (220cm^2 x 5.8 = 1276). To look at it another way, a single Dayton RS225 has more bass capabilities than the 24 drivers combined.

    But wait! This is a sealed speaker. Therefore, it is only equal to a single average 8" woofer in a sealed box! A ported speaker can play 3-10dB louder than the sealed equivalent in the bass region depending on the size of the enclosure and port. Let's be conservative, and say the ported speaker reduce the displacement requirement by half (in reality it is more, a lot more if it is around tuning). Taking that into account, now the CBT's bass capabilities is equivalent to a 6.5" woofer with 4.5mm of excursion, which is very average for a 6.5".

    While a CBT looks big, it doesn't actually have nearly as much displacement as you would think. On the other extreme, there is my speaker, which has the equivalent displacement capabilities of a sealed 12" subwoofer with 10mm Xmax in a speaker the size of an overnight sensation by stuffing it with drivers. That said, even if the displacement is available, utilizing them is not easy as the currently available commercial DSPs don't have the proper protection circuitry to allow for a lot of bass boost without the risk of easily bottoming out the speaker.

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    • #17
      I understand that, why not use some bigger drivers?

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      • #18
        Originally posted by xmax View Post
        I understand that, why not use some bigger drivers?
        Then you need tweeters, and a CBT with tweeters creates additional complexity and substantially more cost.

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        • #19
          Originally posted by Jim Griffin View Post
          Don,

          Have boxes. Will travel.

          Jim

          Holy cow, Batman! Just have to find a venue now.

          I think I hear a difference - wow, it's amazing!" Ethan Winer: audio myths
          "As God is my witness I'll never be without a good pair of speakers!" Scarlett O'Hara

          High value, high quality RS150/TB28-537SH bookshelf - TARGAS NLA!
          SB13/Vifa BC25SC06 MTM DCR Galeons-SB13-MTM
          My Voxel min sub Yet-another-Voxel-build

          Tangband W6-sub

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          • #20
            Don, realize I have lots to do before the music plays--finishing, assembly, testing, etc. will consume the next month. I may have them ready to show at the Kentucky DIY in mid-November but with minimal listening time. With holiday stuff and a Florida vacation it will push things into next year.

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            • #21
              Originally posted by xmax View Post
              I'm no expert on line arrays and with all due respect, seemingly with all that Sd one could be designed with ample low end,
              is there something with a line array that makes that not practical? I see subs are often recommend with them.
              Line arrays are build and designed to present different type of virtual imaging. As far as frequency response of a line array speaker goes, it presents challenges just like conventional speaker designs.
              Having said that, you could build a full range driver array, 2-way or 3-way array or even design a bass array.
              What you do get with the array is a huge life-like image and incredible dynamics.
              http://www.diy-ny.com/

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              • #22
                Originally posted by r-carpenter View Post
                Line arrays are build and designed to present different type of virtual imaging. As far as frequency response of a line array speaker goes, it presents challenges just like conventional speaker designs...
                Absolutely, like any other tool.

                What is the arc angle?

                "Not a Speaker Designer - Not even on the Internet"
                "If the freedom of speech is taken away, then dumb and silent we may be led, like sheep to the slaughter."

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                • #23
                  Originally posted by Sydney View Post

                  What is the arc angle?
                  36 degrees

                  My "No-Name" CC Speaker
                  Kerry's "Silverbacks"
                  Ben's Synchaeta's for Mom
                  The Archers
                  Rick's "db" Desktop CBT Arrays
                  The Gandalf's

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                  • #24
                    They look great... but I bet you have almost as much engineering in the box and packaging as in the actual speakers. I hope Jim keeps the boxes for any future travels!

                    TomZ
                    *Veneering curves, seams, using heat-lock iron on method *Trimming veneer & tips *Curved Sides glue-up video
                    *Part 2 *Gluing multiple curved laminations of HDF *Cello's Speaker Project Page

                    *Building the "Micro-B 2.1 Plate Amplifier -- Part 1 * Part 2 * Part 3 * Part 4 * * Part 5 'Review' * -- Assembly Instructions PDF

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                    • #25
                      Originally posted by tomzarbo View Post
                      They look great... but I bet you have almost as much engineering in the box and packaging as in the actual speakers. I hope Jim keeps the boxes for any future travels!

                      TomZ
                      Thanks Tom. Yea, I highly underestimated time and materials on the packaging for these but will have a better feel for something like this in the future. "Adequate packaging" takes on a whole new definition when it comes to enclosures being transported by UPS or FedEX, man they are rough on stuff. Jim did tell me he plans to reuse the packaging for transporting them to future events.
                      My "No-Name" CC Speaker
                      Kerry's "Silverbacks"
                      Ben's Synchaeta's for Mom
                      The Archers
                      Rick's "db" Desktop CBT Arrays
                      The Gandalf's

                      Comment


                      • #26
                        Originally posted by Jim Griffin View Post
                        Don, realize I have lots to do before the music plays--finishing, assembly, testing, etc. will consume the next month. I may have them ready to show at the Kentucky DIY in mid-November but with minimal listening time. With holiday stuff and a Florida vacation it will push things into next year.

                        No worries - I've been trying to have a DIY for several years.
                        With some luck, Spring next year may work for everyone.

                        I think I hear a difference - wow, it's amazing!" Ethan Winer: audio myths
                        "As God is my witness I'll never be without a good pair of speakers!" Scarlett O'Hara

                        High value, high quality RS150/TB28-537SH bookshelf - TARGAS NLA!
                        SB13/Vifa BC25SC06 MTM DCR Galeons-SB13-MTM
                        My Voxel min sub Yet-another-Voxel-build

                        Tangband W6-sub

                        Comment


                        • #27
                          Jim, what significant changes would you make to your line array white paper? Do you intend to publish the changes to account for the comb filtering? Thanks.

                          Hong
                          Some people are addicted to Vicodin. I'm addicted to speaker building.

                          The Chorales - Usher 8945A/Vifa XT25TG Build
                          ESP Project 101 Lateral MOSFET Amplifier
                          LM4780 Parallel Chipamp
                          Sonata Soundbar Project
                          The Renditions - Active/Passive Towers

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                          • #28
                            Hey Kevin and Jim! These look like an excellent successor to the CBT array project. Not sure I'll be able to make any of the mentioned DIY events to see them in person, but maybe MWAF 2018 or InDIYana 2018? Thanks for sharing the details that you have thus far. Keep up the great work!
                            Voxel Down Firing with Dayton SA70
                            Translam Subwoofers - The Jedi Mind Tricks
                            The Super Bees - Garage 2 way

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                            • #29
                              Originally posted by bcodemz View Post

                              Then you need tweeters, and a CBT with tweeters creates additional complexity and substantially more cost.
                              Don't some of these designs use tweeters?

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                              • #30
                                Originally posted by xmax View Post
                                Don't some of these designs use tweeters?
                                Yes.... Don's own: 19 mids and about 117 tiny tweeter thingies(what fun with all that soldering): http://www.xlrtechs.com/dbkeele.com/images/_MG_2364.jpg

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