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Thread: Late 70's Custom JBL Builds - Info gathering mission - All help truly appreciated

  1. #1
    Member medwardb's Avatar
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    Late 70's Custom JBL Builds - Info gathering mission - All help truly appreciated

    Hi folks,
    I purchased a pair of custom JBL builds from an old gentleman (86) recently who built these back in the 70's. The cab dimensions are:
    18"in wide, 14-1/4"in deep & 28-3/4"in high.
    The driver compliment, [ea.] is:12"in 124H woofers, 2105 mids & 2405 HF rads. At the time of purchase the 124H's needed to be re-surrounded, and this I accomplished with the very kind assistance of Rick C. in Florida and his high quality JBL surround kits.
    [Thanks again Rick! Breakin' them in as I write. They're great. I'll be talking to you again soon. Very soon.]
    The cabinets are almost as impressive as the driver compliment. 7/8"in think solid marine grade ply w/ walnut vaneer. Nice and heavy.
    There is also a 1/2"in lag bolt goning through the rear straight through the front baffle, half-way up from bottom up but slightly "inside" from center (hmm?). Each "plane" "sandwiched" between a pair of nuts & 1.5"in washers inside & out. I imagine for front baffle and overall support. [The horizontal line on the right speaker is a stain drip, not a crack]
    Grills are quite solid also with 3 lateral 7.5" x 1."in. slots in each side due to their 2-3/4"in. thickness.
    Cabinet construction is s.o.l.i.d. solid. Not sure about which model the design que was taken from though not like any cab design I've seen as I recall.
    As for the crossovers they're HUGE. I'd say that the layout takes up most of the inside of one side of the 28"in. high cab!
    They provide two controls similar to that which is found on L100's/4311's etc. But I'm not sure if they are "Brillience & Prescence" or just [0-100 or cut-unity-boost] attenuation for mids and tweets.
    (I'm exploring the possiblity of opening one of one cabs for a clear pic and possible upgrade of the crosssovers, as the rear panels seem to be connected using "Allen" head type screws at the very least.)
    Crossover component quality is high, and build quality is capable though, from what I can see, was done by someone that had obviously built on this level before. The 3 inductors (at least the size of hocky pucks) are hand built and very well done.
    So, I've included some pics and am open to all impressions, info and hints.
    If and when I get the rear off of one I"ll include pics of the crossovers and attempt an interpretation of a schematic.(..uh,huh..)
    I'm very curious about whether there were home designed or taken from existing crossover design.
    Thanks to all for reading through this and letting me benefit from your cumulitive knowledge and experience. This is a great site and I truly appreciate everyones participation. Things are kind of rough here in Michigan but when I get the chance I will be making a $ contribution to the site in appreciation. Peace everyone,
    M.Edz
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    Was the seller 86 when he built the boxes or when he sold them to you? ...Anyway, 86 is not old.

    The pair look like a great score to me. If that time period is correct, I would have expected the slots to be 077s, but I could be wrong.

    It would be interesting if you could post a picture of the crossovers.

    What else can the young man who sold them to you tell you about their history?

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    Moderator hjames's Avatar
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    Generally, access to the big boxes is by removing the clamps and the woofers.

    Lay a towel or something like a small rug down on the floor.
    Lay the speakers down on their back.
    Loosen the clamps and carefully lift the woofers from out of the cavity.
    Using masking tape or a sticky tab, LABEL THE WIRES and the back of the woofer so you KNOW which wire connects to which connector.
    Remove the woofers and carefully put them aside.

    Now you can photograph or examine your crossover or whatever on the inside.
    2ch: WiiM Pro; Topping E30 II DAC; Oppo, Acurus RL-11, Acurus A200, JBL Dynamics Project - Offline: L212-TwinStack, VonSchweikert VR-4
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    Member medwardb's Avatar
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    Reply: Rob:...70's JBL Customs:

    Quote Originally Posted by robertbartsch View Post
    Was the seller 86 when he built the boxes or when he sold them to you? ...Anyway, 86 is not old.~
    ...What else can the young man who sold them to you tell you about their history?
    Rob,
    The gentleman was 86 when he sold them to me. [He'd be over 110 otherwise.]
    This was just before he relocated to, I believe, an assisted living community. He was a chemest and built them in the late '70's. As for the high freq rad.
    I"m not ab.positive about it being a 2405 or an 077. I didn't take it out though I did take out the woofer and the mid. Since he's moved I no longer have accesss to him. He had a beautiful pair of 3 way Dynaudio cabs he had built around that time also. Sounded great.
    They weren't for sale So, I can learn no more about them from him.
    His name is G. Valentine. A very nice man indeed, he was to me.
    I realy wish I could have spent more time with him.
    Thanks Rob,
    M. Edz

  5. #5
    Member medwardb's Avatar
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    Reply:[hjames] ....70's Custom JBL's...

    Quote Originally Posted by hjames View Post
    Generally, access to the big boxes is by removing the clamps and the woofers.~
    ....Remove the woofers and carefully put them aside.
    Now you can photograph or examine your crossover or whatever on the inside.
    hjames,
    thanks for the reply and instructions. I thought I mentioned in the original post that I had replaced the surrounds, so, I'm good with a good deal of repair. But thanks, I do appreciate it. Honestly I realy didn't think about putting a digi-cam inside the cab and trying to take an individual or composite pic of the crossover w/the aid of a flash.
    Hence, not needing to open the back of the cab. There's a good deal of insulation, and the inner enclosure for the mid, but hopefully it should be possible.
    Though that would be the only way to do any repairs on it. As I mentioned it's on a rather large board that has to be at least 18"x14" I'd guess. So taking it out of the woofer port is in no way possible. I"m going to attempt to take photos of the crossover now. Wish me luck, and thanks again for your reply.

    -M.Edz>

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    Senior Member Russellc's Avatar
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    Looks sort of like a DIY JUBAL, or L-65. Is the piece inside the tweeter slot black or glass?

    Russellc

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    Member medwardb's Avatar
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    Quote Originally Posted by Russellc View Post
    Looks sort of like a DIY JUBAL, or L-65. Is the piece inside the tweeter slot black or glass?

    Russellc
    ..it's black.

    -M.Edz>

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    To me it looks like a DIY cab as well. The 2405 came out very early 70's so it could be either. If the phase plug is metal it will be a 2405, if plastic it will be an 077. So people have been known to paint the clear plastic phase plugs black for some strange reason. But either way they would be a good find.

    Allan.

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    Member medwardb's Avatar
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    Re: Phase Plug (2405)

    Quote Originally Posted by Allanvh5150 View Post
    To me it looks like a DIY cab as well. The 2405 came out very early 70's so it could be either. If the phase plug is metal it will be a 2405, if plastic it will be an 077. So people have been known to paint the clear plastic phase plugs black for some strange reason. But either way they would be a good find.

    Allan.
    Hi Allan,
    thanks for the info about the phase plugs. As far as I can tell without
    taking the thing apart the phase plug is black and metal. I tapp'd it lightly
    with a piece of plastic and got a metalic sound, so..
    When I get around to photographing the crossovers, hopefully soon, I'll attempt popping them out for a look see.
    Thanks again Allan,

    -M.Edz>

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    Senior Member Doctor_Electron's Avatar
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    Can you put up some pictures of the crossovers, and component values?

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    Senior Member spkrman57's Avatar
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    Port stuffed?

    I was curious why use ports and stuff them???

    Ron
    JBL Pro for home use!

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    Member medwardb's Avatar
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    Crossover Pics:

    Quote Originally Posted by Doctor_Electron View Post
    Can you put up some pictures of the crossovers, and component values?
    Hello Doc, and thanks for the reply.
    I have been planning to try to get photos of the crossovers while still inside
    the cabs (..the crossovers, not me) as they are too large to remove without
    removing the back of the cab. But I've just been too busy to get to it lately.
    I will accomplish this though. Hopefully within the next few days as I myself
    am very interested in their makeup.
    I'll then try to accompany the pics with component values as well.

    Thanks again Doc,

    -MEdz> *

  13. #13
    Member medwardb's Avatar
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    Re: Stuffed Ports:

    Quote Originally Posted by spkrman57 View Post
    I was curious why use ports and stuff them???

    Ron
    Hi Spkrman57, thanks for the question? I myself kind of wondered this as I was replacing the woofers that I had re-foamed. I didn't design these and I didn't build them either. (Please refer to first post for thier history)
    I've been meaing to unstuff them and see what I get and I think I'll do that today if I get a chance to A-B them in this fashion.
    I'm curious as to wether anyone else does this with their ports and for what reasons.
    I'll let you know what I hear soon with the A-B testing of the stuffed and unstuffed ports.
    Thanks again SpkrMan57,

    -MEdz> *

  14. #14
    Senior Member spkrman57's Avatar
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    Do you have a woofer tester?

    You could test it in the current state of the ports stuffed, then test it without.

    Regards, Ron
    JBL Pro for home use!

  15. #15
    Senior Member duaneage's Avatar
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    Stuffing the ports at best could be described as a aperiodic vent. Dynaudio pioneered this approach. Basically it is a restrictive vent for a sealed box system that allows some relief at resonance. Usually they are on the rear of the cabinet. A proper sealed or vented box would probably be a better bet, I am not familiar with the `124 driver enough to comment on tuning or box size but it looks large enough to be vented.

    In the end if you like the performance that is what counts. Just watch out for unloaded drivers at low frequencies that can jump the gap at high volume. Almost any tuning works at low power, at higher volumes the box and respective tuning protects the driver and controls excessive cone movement.
    Why buy used when you can build your own?

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