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Jim's new CBT Arrays

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  • Kevin K.
    started a topic Jim's new CBT Arrays

    Jim's new CBT Arrays

    Mr. Griffin contacted me recently and inquired about cutting/assembling some Array cabinets for him. He desired something similar to the "Epiques" but wanted to utilize a different driver (SB65WBAC25-4) along with make a few minor changes to the cabinets (1" wider, braces, roundovers). After a few emails back and forth, I presented him with a CAD model for approval and we started the project.


    I didn't take a lot of pictures during the build process, sorry guys. Jim did give me permission to post what I have for you to see. If you have questions about the cabs, I'll gladly try to answer. If it's about the details of the design and the "why's", Jim will chime in to answer those.

    Here are the CAD screenshots (in greyscale), not sure what color Jim will be painting the cabs. Believe he has a local painter in mind.

    Click image for larger version

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    One of the first hurdles would be coming up with a way to secure the removable baseplates to the towers. Jim was prepared to use bolts and nuts which would require him to be able to get his hands in through the back of the tower to start the nuts and tighten them. I suggested we look at incorporating a plate with nuts welded to them so he wouldn't have to do that. He liked the idea and after giving this some more thought, I suggested the plate be changed to a bracket with legs that could also be secured to the sidewalls. This would increase the overall strength of the assembly and spread out the work load. Had some 1/4" thick 3"x3" angle iron on hand and decided to use that. Overkill, yep. 1/8" steel would probably have sufficed but the extra weight at the bottom of the array isn't gonna hurt us.

    After cutting 1.5" off of two pieces of the angle iron, they were welded together and then milled flat on the bottoms. This was followed by drilling holes for 5/16" bolts, tapping the holes and then welding nuts for even more threads to engage with the bolts. Sandblasted them next and then applied a Rustoleum paint and primer in one.

    Click image for larger version

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    More in the next post.

  • Kevin K.
    replied
    Originally posted by indyhank View Post
    Hi Kevin, Jim sent me your contact info and I'll send you a note asking about your CNC shop, etc. I'm in Austin. First question: did you consider using Baltic Birch rather than MDF? I've always built speakers out of MDF, but considering BB for next project.
    Hi Hank, welcome to the forum. No, I didn't consider BB because Jim specified MDF, probably since he will be having these painted. The Arrays could have been built out of either otherwise. Up to this point, everything I have built in the past has always used MDF as the substrate. There are "Pro's and Con's" to both materials and I'm not a fan of splinters, hence my choice to use MDF.

    Leave a comment:


  • indyhank
    replied
    Hi Kevin, Jim sent me your contact info and I'll send you a note asking about your CNC shop, etc. I'm in Austin. First question: did you consider using Baltic Birch rather than MDF? I've always built speakers out of MDF, but considering BB for next project.

    Leave a comment:


  • rickcraig
    replied
    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.
    I'll add to what Jim said. The lower group (bank) of drivers are driven with no attenuation. This means they are taxed more with greater excursion and the small 2.5" SB drivers have a limited amount of excursion. Adding on EQ to extend the bass makes it even more difficult; as a result, adding a sub is the way to go.

    Leave a comment:


  • malboro2
    replied
    Originally posted by xmax View Post

    Now that would be AWESOME!
    I'M building a 4-way, electronically crossed. Per channel: 1- 12 inch sub(equalized sealed 27-100), 1- 8 inch mid sub(100-600), 20- 2.5 inch mids, 10- Planars. I already built an awesome 8 foot high 3 way: with 2 12's, 34 mids, and 64 dome tweeters. This is for downstairs in the living room where the WAF has more input. Same Tube/cylinder cabinet construction though.

    Leave a comment:


  • Jim Griffin
    replied
    Several of you appear to not know about the two-way CBT36 that Don Keele developed and provided to P-E for a kit build a few years ago. That array was developed in conjunction with Audio Artistry. See:

    https://www.parts-express.com/audio-...r-kit--301-980

    Leave a comment:


  • xmax
    replied
    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.
    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.
    Now that would be AWESOME!

    Leave a comment:


  • donradick
    replied
    Originally posted by Paul K. View Post
    I wish I had Kevin's wood-working skills; many times I've been happy to still have all my digits and managed to assemble a cabinet that's completely square where is should be!
    Paul

    My wife will not let me live down those cabinets that were 1/8 inch out of square.
    I strive to do better......

    Leave a comment:


  • Kevin K.
    replied
    Originally posted by Paul K. View Post
    I wish I had Kevin's wood-working skills; many times I've been happy to still have all my digits and managed to assemble a cabinet that's completely square where is should be!
    Paul
    Thanks Paul! Your cabinets leave nothing to be desired, they're always flawless and beautiful.

    Leave a comment:


  • Paul K.
    replied
    I wish I had Kevin's wood-working skills; many times I've been happy to still have all my digits and managed to assemble a cabinet that's completely square where is should be!
    Paul

    Leave a comment:


  • Kevin K.
    replied
    Originally posted by xmax View Post
    Don't some of these designs use tweeters?
    Originally posted by malboro2 View Post

    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
    Here's another one the two of you may not have seen.

    http://techtalk.parts-express.com/fo...c-40-cbt-array

    Leave a comment:


  • malboro2
    replied
    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

    Leave a comment:


  • xmax
    replied
    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?

    Leave a comment:


  • KEtheredge87
    replied
    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!

    Leave a comment:


  • hongrn
    replied
    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

    Leave a comment:

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