JBL L 100 mystery cabinets

Discussion in 'Speakers' started by 808_state, Sep 4, 2017.

  1. 808_state

    808_state Active Member

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    I was recently browsing Troels Graveson's upgrade page when I saw these mod cabinets for the JBL L100's. I thought they looked stunning and emailed Troels and he told me he no longer has the builder's email. The only info he has is "Brandon US"...might anybody here recognize these beauties or have more info? 3.jpg 2.jpg
    They appear as though the designer put a lot of time and thought into them and I'd like to know more about them.
     
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  2. slimecity

    slimecity Super Member

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    Those are wicked. Love the xover on display like that
     
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  3. Gazdatronik

    Gazdatronik Super Member

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    Maybe an L100 but if they had designed one to properly optimize the driver compliment. I see a lot more inductors there than an L100 would normally have. I bet it sounds great.
     
  4. turboyam

    turboyam The Kenwood fan!

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    The port (s) are probably in the back too?
     
  5. 808_state

    808_state Active Member

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    That's my guess and it appears as though the cabinet is modular with an upper section housing the drivers and a lower section housing the crossover/electronics. Do they come apart? This creation must have an amazing back story and I have so many questions! :biggrin:
     
  6. R Swerdlow

    R Swerdlow Member

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    I'd guess the cabinet shown above is sealed. The standard L100 cabinet is about 1.8 ft³, with a roughly 3" diameter port. That's too small for the 123A woofer, but JBL decided to keep the cabinet small so they could use it as a studio monitor.

    Better 123A bass performance comes with larger sealed cabinets, in the range of 3.9 to 5.9 ft³.
    Q curves.GIF
     
    Last edited: Sep 4, 2017
  7. 808_state

    808_state Active Member

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    Well hard to say if they're ported or not but I'm guessing he at least doubled the volume and that red curve looks pretty nice. I know Troels designed a diy cabinet to increase the volume but this guy made a definite statement with these. With substantial mass and non-parallel surfaces I bet they sound amazing.
     
  8. R Swerdlow

    R Swerdlow Member

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    Red curve, 109 liter, 3.9 ft³, Q = 0.8, F3 = 44 Hz

    Dark blue curve, 167 liter, 5.9 ft³, Q = 0.7, F3 = 39 Hz
     
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  9. 808_state

    808_state Active Member

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    Swerd, have you compared the Murphy and the Jantzen/Gravesen crossover designs? If so, does one have an advantage over the other? Is it possible to work the L-pads into the design or would it better to fashion a simple switch for toggling between the old and new crossover?
     
  10. R Swerdlow

    R Swerdlow Member

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    I have never heard L100 speakers with the Jantzen/Gravesen crossover. Troels Gravesen has a good reputation among DIY builders, so I believe his design should also sound good. I only know the Dennis Murphy design, which I am certain sounds good. Dennis Murphy also has an excellent reputation both as a DIY speaker designer, and as designer for the internet-direct sold commercial brands Salk Speakers and Philharmonic Audio. Dennis's crossover makes the L100's frequency response curve as flat a possible and tames much of the mid-range driver's misbehavior. The bass peak around 70-80 Hz comes from the too small cabinet, and only a new much larger sealed cabinet could fix that.
    I think the L-pads are a problem best avoided by eliminating them. They always oxidize and pit over time, causing major noise or drop outs if you move them. If you replace the L-pads with new ones, they eventually suffer from the same problem.

    Dennis Murphy's new crossover has built-in resistor padding to create a balanced neutral sound. I, and others as well, found that pleasing and eliminated any desire to raise or lower volume of the mid-range or tweeter.

    One of the people who built the new Murphy crossover fashioned some elaborately wired switches to allow toggling back and forth from the original JBL crossover (including the L-pads) to the new design. He posted under the name leesonic starting at post #73 http://forums.audioholics.com/forum...bl-west-coast-sound-becomes-the….25014/page-4. Unfortunately, the extensive photos of his work are now gone, probably they were on photobucket. He occasionally posts here. @leesonic, If you're reading, please post your switchable crossover schematic and photos again.

    You should probably read through that Audioholics thread for all of leesonic's posts. I'm not certain, but I recall that he later decided he liked the new crossovers much better and rarely switched back to the original JBL crossovers.
     
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  11. leesonic

    leesonic Hold on, here comes the bass. Subscriber

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  12. 808_state

    808_state Active Member

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    Thanks Swerd and Lee! I actually found the above thread not long after I posted the message above.

    My L-pads are in good shape (the previous owner was a speaker repair guy/JBL fanatic and cleaned them up fairly well) and it would be nice to at least be able to go back and forth (not necessarily for individual drivers).

    Here are my L-100's, they're in decent shape (I'm just missing one peg for the grilles):

    0912171719-1.jpg
     
  13. jobrewer1983

    jobrewer1983 AK Subscriber Subscriber

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    Not sure on the builder, or if they are just a one off.. Nonetheless they sure are bitchin!

    Kind Regards,
    John
     
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  14. 808_state

    808_state Active Member

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    I'm really hoping this guy will stumble upon this so we can get a detailed thread on the process & final sound result.
     
  15. jobrewer1983

    jobrewer1983 AK Subscriber Subscriber

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    You and me both, I've seen some hookey builds on the site, but this set looks pretty well made.

    Kind Regards,
    John
     

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