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  • JBL rebuild

    I've been commissioned to repair and improve the sound system for a local fraternity. They have four 15" 2way JBL PA cabinets and a Cerwin Vega FLH.

    They have a mishmash of electronics. Some good, some ok, some not so good. The amps consist of a pr of Crown 36x12s and a Crown xls2000. The mixer is a Gemini DJ board and there is a Berhinger cross over that is not being used currently.

    All four cabinets have blown tweeters and they had one cabinet actually catch fire. When i got to it, the cabinet was still covered in extinguisher media lol. The above crossover pic is the carnage inside. And the drivers are the "fix" someone else did over the summer. Ugh! They were told that original parts were used. Guess not!
    https://www.facebook.com/Mosaic-Audi...7373763888294/

  • #2
    Clueless Silly Frat Rats
    "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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    • #3
      Lol yep. Gains were cranked, eq maxed.
      https://www.facebook.com/Mosaic-Audi...7373763888294/

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      • #4
        Not a shocker there. Tone controls/eq must be touched if you catch eyesight of the dials/slides/buttons.
        Builds - C-Killa - Speedsters - LithMTM - Talking Sticks - Pocket Rockets - Khanspires - Dayton RS Center - RS225/28A - Kairos - Adelphos - SEOS TD12X - Dayton 8 - Needles - 871S - eD6c - Overnight Sensations - Tritrix (ported) - Lineup F4 - Stentorians - The Cheapies - Tub Thumpers - Barbells - Tuba HT - Numerous subwoofers - probably missing a few...... :p

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        • #5
          Nice project. Did they insist on going with original parts, because if not I'd suggest going with B&C drivers instead. It's interesting that there seems to be no protection in the x-over (and a lot of resistors). CV included protection in even the cheap PCX-153 build (though the ones my cousin had in his night club still tended to burn because of bad x-over design resulting in a 2-ohm load through the midbass/midrange region.
          Brian Steele
          www.diysubwoofers.org

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          • #6
            Nope, I can use what I want essentially, budget of course the concern. More than likely, I will be using Eminence drivers
            https://www.facebook.com/Mosaic-Audi...7373763888294/

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            • #7
              adding fuses would probably be a good addition, ya?

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              • #8
                Originally posted by hardcorecap View Post
                adding fuses would probably be a good addition, ya?
                Yes, but I will probably use a circuit breaker. I'm also adding a compressor and a locked cabinet for the amps.
                https://www.facebook.com/Mosaic-Audi...7373763888294/

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                • #9
                  Originally posted by isaeagle4031 View Post

                  Yes, but I will probably use a circuit breaker. I'm also adding a compressor and a locked cabinet for the amps.
                  Where I've seen difficulty is people adjusting the gain up for a softer tune and then forgetting to adjust before dropping the needle on some house-shaking party song.

                  Will a compressor allow you overcome this sort of issue?

                  I'm not familiar with how compressors work.

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                  • #10
                    Originally posted by philthien View Post
                    ...Will a compressor allow you overcome this sort of issue?...
                    Not really - especially in this situation
                    From a Tech note of setting up limiters "Relying on peak limiting for power control may be very harmful and can lead to speaker destruction. An important thing to consider is that peak limiting can raise up the RMS power level."
                    ( besides "killing" the transients )
                    and a locked cabinet for the amps.
                    A locked Liquor Cabinet would be helpful
                    Last edited by Sydney; 11-04-2017, 10:57 AM.
                    "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."

                    Comment


                    • #11
                      I suspect that these young men care more about sound pressure level than sound quality

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                      • #12
                        Originally posted by isaeagle4031 View Post
                        All four cabinets have blown tweeters and they had one cabinet actually catch fire.
                        That right there shows how the system was and will continue to be operated, so unless you do something to control the amount of power the speakers are seeing you're just wasting money buying better drivers. I'd suggest only spending what you need to make the speakers functional again(rebuilt crossovers and new CD diaphrams) and then buy a PA processor for it and setup conservative limiting.

                        If these boxes were biamped with the 36x12s then there is no need for a full passive crossover, but it wouldn't be a bad idea to setup an idiot proof connection system such as a patch panel with NL4 speakons on it.
                        Paul O

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                        • #13
                          Indeed - Indifferent ( probably drunken ) untrained "operators" ( as opposed to a singular sober trained individual ) who will use a device improperly* - raising the RMS level.

                          Gains were cranked, eq maxed.
                          * Case in point ( on a Gemini DJ board no less )
                          "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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                          • #14
                            Could also use a bulb(s) in the CD circuit to help protect it at high levels like the way Danley Sound does.

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                            • #15
                              The amps were not used correctly. Part of the overall problem as well. That too will be addressed. I may do away with the passive altogether and run thru the Berhinger crossover they have. NL4 connects are also being installed.
                              https://www.facebook.com/Mosaic-Audi...7373763888294/

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