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Thread: Another DIY 4425

  1. #1
    Senior Member John W's Avatar
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    Another DIY 4425

    Another DIY 4425



    I am in the process of gathering the components for a pair of 4425 monitors. After reading parts of the quick and dirty 4430 thread I think I want to base the crossover off the NL200t3 network. Both networks use a 12 in woofer, the 2416h driver and cross over at 1200hz. Other than that, I am not sure on differences between the 120T3 and the 2214H woofers.

    I combined the low pass from the 4425 with the high pass of the NL200t3 and came up with this:

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  2. #2
    Senior Member John W's Avatar
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    This will be cheaper and easier to implement than the stock 4425 crossover, and if it falls flat, I can always rebuild the high pass. Has anyone tried anything similar?

    Also, I can duplicate the 4425 box using the measurements from the Technical Manual, but I am unsure of the port dimensions. For a 1.9ft3 box tuned to 34hz I calculate 2 ports 2 in diameter x 6.25 inches. Can someone with a 4425 measure the ports to verify this?

    Thanks for any input.


  3. #3
    Senior Member frank23's Avatar
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    Well, I haven't simulated the crossover, but I don't think this will work. The coil in the low pass is 3.8mH, a fairly large value is seems to me. The cap in the high pass is only 2.2uF, a fairly low value. Looks like there will be a large empty hole in the middle...

    I'm sorry I don't know what the NL200 is, but I think the 4425 horn needs compensation as it is a full biradial like the 2344 horn on the 4430 and this crossover does not seem to provide it.

    I have both 4425 crossovers, horns and 2416 drivers lying around, But I think it would be too much hassle to send them to the USA from Europe.

    I think the 4425 crossover is the 3124, look for those schematics. Unless you take a whole different route and design your own, there is no shortcut in JBL crossovers, they do what needs to be done I think.

    frank

  4. #4
    Senior Member John W's Avatar
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    This is good input:

    Here is a link to the l200t3, which I guess is fairly rare:

    http://manuals.harman.com/JBL/HOM/Te...200t3%20ts.pdf

  5. #5
    RIP 2011 Zilch's Avatar
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    It'll likely work fine. Use the parts list I provided in the Q&D thread for the HP.

    I sent the ones I made to Robh, who is building similar.

    If you want even simpler, just build the complete NL200t3 for starters.

    I played it with 2418H-1 and 2426H, both with 2235H in B380, with good results.

    Frank doesn't understand the circuit yet. The 2.2uF cleverly provides the requisite compensation.

    The 4425 ports are 2.5" x 6" deep here....

  6. #6
    Senior Member John W's Avatar
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    Thanks for the port sizes. I guess for starters I will try the stock NL200t3.

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    John / Zilch

    - One thing to watch for in this design exercise is a possible efficiency mismatch between the horn and the woofer . It might be necessary to insert a variable Lpad in the horn circuit for easier matching.

    - John, If you tire of waiting around for decent 2214 woofs / consider using the 128H .
    It has a long established pedigree . It may require a bit of rework to the lowpass circuit.

    - If it was my project I would start with a newer woofer and get a pair of le120h(s) from Harman . I figure, that if they are good enough to matchup with the 050ti tweeter / then they must be quite good . Here's a bit of info .
    ( The pics are were provided courtesy of Paragon, who pulled this woofer from one of his L90s, for this "Show & Tell" photo-op .

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  8. #8
    Senior Member John W's Avatar
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    Actually, I already have the 2416H/2342 combo and the 2214H woofers should be arriving next week.

  9. #9
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    Quote Originally Posted by John W
    Actually, I already have the 2416H/2342 combo and the 2214H woofers should be arriving next week.
    - Well then, you're good to go !

    - I'll let my comments stand for the future generations reading these archives .


  10. #10
    Senior Member Guido's Avatar
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    John, I did 4425 DIY!

    Why not build the stock networks? It's not that much work.

    Have a look here:
    http://www.audioheritage.org/vbullet...light=4425+DIY
    http://www.audioheritage.org/vbullet...light=4425+DIY

  11. #11
    Senior Member John W's Avatar
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    I saw these posts, its sort of what got me going on the project.

    The complete crossover is still an option. Mainly I want to hear what the simple crossover sounds like, then I can work my way up.

  12. #12
    RIP 2011 Zilch's Avatar
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    Quote Originally Posted by John W
    I guess for starters I will try the stock NL200t3.
    http://audioheritage.org/vbulletin/s...&page=23&pp=15

    Note: If you use my layout, rotate the big inductor 90° horizontal. There was some crosstalk between LF & HF sections as built....

  13. #13
    Senior Member John W's Avatar
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    Note: If you use my layout, rotate the big inductor 90° horizontal. There was some crosstalk between LF & HF sections as built....
    Thanks for the tip. I am debating between the big 15 gauge air core and the Erse 16 gauge iron core inductor. The 3mH air core has a DCR of .64 and the iron core a DCR of .18.

    dB = 20 log ((Rl / Z) + 1) = 20 log (((.64 - .18) / 5.6) + 1) = .69 dB

    Its not much, but I may need everything I can get out of the bottom end.

  14. #14
    RIP 2011 Zilch's Avatar
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    Quote Originally Posted by John W
    I am debating between the big 15 gauge air core and the Erse 16 gauge iron core inductor. The 3mH air core has a DCR of .64 and the iron core a DCR of .18.
    That'd work too, most likely. JBL used laminated core in the 4430 LP.

    I had an L-Pad on the HF output, but never used it. Turns out from the impedances that a 4-Ohm L-Pad would be required so's not to mess up the compensation frequency.

    Next ones I'm building will have biased HF, as well. Just a couple of bucks more to do it, since there's only one capacitor. I'd try a pair of 4.3 uF for starters there....

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