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Thread: New crossover?

  1. #1
    Junior Member joetech's Avatar
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    New crossover?

    I have some L-88s that I have been tweaking for about a year now. I have replaced the original 8uF cap with a new polycap and upgraded the binding posts. I have added more fiberglass to the back. Now I have gone and replaced the old LE25-1 tweeters with some 035Tiís. I must say they sound pretty darn good. Both the old and new are suppose to cross at 3 kHz.
    I found a crossover formula datasheet at www.mhsoft.nl and http://ccs.exl.info/calc_cr.html#lpad both gave me a whole bunch of different values for one thing. A first order xover shows using a 13.25 mH inductor on the Woofer and a 13.25 cap on the tweeter. Does the fact that there is an inductor here change the value required for the cap?
    I have also looked at some of the crossovers that JBL uses for the L1 and L20T both of which are 2 ways with different woofers instead of my 123a.
    Question is, should I make a new xover? Right now the modeling program shows a x over point of5000 with an 8uF cap. Below are the T/s specs I have found on drivers.

    035Ti 123a
    Re 4 8
    Fs ave 1900 25
    Z max ave 15 ?
    F1 ave 1500 ?
    Qms @3 5.3
    Qes @1.5 .54
    Qts @ 1 .49

    Somewhere on this forum someone published the specs for the Le25 and the 035Ti and 035TiA . Above are an average for the measurements he found. The 123a are the specs from unibox. I wrote down the specs for the 035 and now I canít find the thread to write out the specs on the Le25. Iíve looked at many threads here on the L88, 035 L100 etc. and I am very confused. It seems that plugging the port is the way to go but in my situation it may not be. My main listening room is 13í wide x 15í The speakers are on the bookshelf (appropriate enough) about 40Ē off the floor to clear some heavily padded furniture and thatís the only place they fit. They are about a foot from a very short wall. Both sides open up with large archways to other rooms. A 6ft archway on the left to a 10x10 room and on the right a 9í archway into a room 14x15 so I get almost no gain from the walls. The 035s have opened up the sound stage. Being better at dispersion than the old cone tweeters and not as beamy. I must say I like them very much the way they are but I always say if it isnít broke tweak it.
    I see lots of options but none of the thread Iíve read on this and other forums seem to match. Do I copy a later JBL crossover even if it isnít a 123a woofer? Anything close? Do I use a 1st order xover with an inductor? Change the cap only?

  2. #2
    RIP 2011 Zilch's Avatar
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    It's gonna cost under $10 to try the port plugs. Notwithstanding boundary reinforcement, they're boomy by design. The plugs strip off the boom and leave the rest.

    Yes, when you go from 6 dB to 12 dB filters, the cap value changes.

    I've got filters on the woofers, but my design isn't final. Start with a Zobel and an inductor....

  3. #3
    Junior Member joetech's Avatar
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    to zilch

    yes I've read the long thread from a (few months ago?) about the closing of the port. I like the idea of using a plumbing test plug. But wasn't all that on a 3 way L100? Temporary and easy to remove if I don't like it. What value of inductor do you suggest I put on the woofer? Also, if I'm not mistaken, the Re of the LE25 is 8ohm and the 035 is 4ohms. I know this changes things as well. A zobel is an interesting idea but isn't a L-pad really the same function only more variable?

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    RIP 2011 Zilch's Avatar
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    Most of the work in that thread was done using L88, including the damping studies:

    http://audioheritage.org/vbulletin/s...070#post123070

    L100 was merely a "Sidebar."

    Zobel flattens the impedance so that the inductor works predictably.

    No L-Pad in the woofer circuit.

    Look to standard designs for an inductor value starting point....

  5. #5
    Junior Member joetech's Avatar
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    what values?

    Yes I know the Lpad is just for the tweeters. It was suggested on another forum (yes I've been seeing another forum) That a 1.1mH choke on the woofer and 8uF 2 cap on the tweeter and a 2ohm resistor be used but they didn't say if the restitor was in parallel or series. I assume one cap was in parallel and the other in series? I didn't follow up at the time for clarification.
    Does this sound like a good approach. I plan to check out in more detail the xovers for the L20t and L1 that both used the 035Ti. Any thoughts would be appriciated.

  6. #6
    Junior Member joetech's Avatar
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    A-B test to live music

    I went to a Cleveland Orch concert today. They were to play, among other selections, Stravinsky's Symphony in 3 Movements. I have a good CD of this. So, on Saturday I listened to it very closely. Then I went to my shop and made some plugs for the port. I listened again to the Stravinsky and others and the bottom end was less boomy.
    At the live concert, I must say my speakers do sound very good in comparison. Of course, a 3 hour plus time delay isn't a real comparison and nothing can compete with the live sound of a great orchestra in a very well designed venue. However, I wasn't 'suprised' to hear new sounds I hadn't heard before.

    Now my next experiment will be to see if adding a cap to the existing one will make much difference. Right now tweeter has an L-pad and 8mF Cap. That's all. The original tweeter, LE25-1 was 8 ohm. The new 035Ti is 4 ohm. Doing some quick calculations that means the tweeter was coming in at 2500 Hz (literature sayes 3000) but the 035 at 4 ohms is coming in at 5000! (If my calculations are correct.)

    So if I want to bring in the tweeter at 3K again, I need to increase the Cap to 13.25mF. I think I will try to do this by putting in parallel a 5mf cap. and see what happens. If I want to cross at 4000 I would have to go to 9.9 mF so I would put in a 2mF cap. Comments please.

    I know Troels Gravesen is working on redesigning some L-100s I was going to wait to see what he comes up with before I do anything drastic.

    Thanks Zilch for your input. The plug I made works great. I don't need plumbing supplies. I have a lathe. In fact I have 3. 1 wood and 2 engine lathes. I could go into business. Right now the plug is a temp but I think I could modify it to use an O-ring and center bolt to sqeeze the o'ring out and make it very rigid yet removable and flush to the baffle. Made of MDF instead of your silver pine plug

  7. #7
    RIP 2011 Zilch's Avatar
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    Why do you believe the 035 is 4 Ohms?

    Do you hear the difference in the bass response?

    Mr. Widget's test for a good seal is to gently press the woofer cone in about 1/4" and it should return to neutral sluggishly.

    [He said "snail's pace," actually, but slugs are kinda the same thing.... ]

  8. #8
    Junior Member joetech's Avatar
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    035 Ti 4 ohm

    This is a 4 ohm because JBL literature says it is. I also found, a few weeks ago, where someone had measured some 035Tia and 035Ti and all were 4 ohm nominal.
    Yes, I do hear some difference in the bass. Not quite as much 'punch' but a better over all sound. For example, in the Symphony in 3 movements there is a bass drum and tympany. Before the bass kind of overpowered the tympany but now they are more distinct. I just did this on 3 days ago and haven't had time to listen extensively.

    Yes, the woofers do return more slowly than before.
    Last edited by joetech; 03-26-2007 at 07:07 PM. Reason: add

  9. #9
    RIP 2011 Zilch's Avatar
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    http://www.jblproservice.com/pdf/Stu...ies/4410LR.pdf

    DCR spec. is 3.5 - 4.2 Ohms.

    That ain't the impedance.

    The diaphragm kit is D8R035tiA, 8 Ohms nominal....

  10. #10
    Moderator / Treasurer/Marketplace Czar boputnam's Avatar
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    Quote Originally Posted by joetech View Post
    ... Of course, a 3 hour plus time delay ..
    Dood - that is a REALLY long room!!
    bo

    "Indeed, not!!"

  11. #11
    Junior Member joetech's Avatar
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    OK I assume it would see 8 ohm because no matter what because I forgot about the L-pad which is 8ohm. So it looks like the tweeters still kick in about 2500. This is the same point the L60T crosses.

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