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Thread: New crossover design for L-100A

  1. #46
    RIP 2011 Zilch's Avatar
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    O.K., L100 enthusiasts, start building crossovers, now!


    The Zobel I came up with empirically is 6 Ohms and 30 uF, yielding a 5-Ohm impedance with the woofer.

    White shows 5.5 Ohms and 31 uF....

    Who'll tackle this with LEAP?

    Are White's models of the drivers good by today's standards?

  2. #47
    Senior Señor boputnam's Avatar
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    Quote Originally Posted by Swerd View Post
    ...it’s all in the crossover, and to a lesser extent, cabinet design. A well designed crossover can make average or even poor drivers sound decent, and a well designed crossover combined with genuinely good drivers can make for a truly excellent speaker.
    So true, and a valuable discovery (worth sharing!). Individual measurements of each driver's response mounted IN the actual baffle and cabinet provide invaluable information as to their contribution to the whole. Designing for that response is the only way.

    Collecting meaningful measurements is key. Can you provide details on the set-up Dennis Murphy uses? I cannot find description on his website. Poor data collection results in a flawed understanding of driver/baffle/cabinet response. Clearly, your results were good, having been based upon representative/reproducable measurements. It would be nice to know how he approaches this.

    Quote Originally Posted by Giskard View Post
    There are really good points that have been stressed again in this thread and I won't belabor them. ... Excellent presentation
    Agreed. From individual driver response and polarity ( ), to baffle layout, crossover point and slopes, and listening impressions (besides just nice plots) - and all that on L100's!!
    bo

    "Indeed, not!!"

  3. #48
    Senior Member DavidF's Avatar
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    Quote Originally Posted by Zilch View Post
    O.K., L100 enthusiasts, start building crossovers, now!


    The Zobel I came up with empirically is 6 Ohms and 30 uF, yielding a 5-Ohm impedance with the woofer.

    White shows 5.5 Ohms and 31 uF....

    Who'll tackle this with LEAP?


    Are White's models of the drivers good by today's standards?


    A pop quiz for true JBL D.Y.I types on the xover schematic on the magazine page 48. What is the translation to cone motion for the polarity scheme as shown?

    DavidF








    “+” x-over leg to woofer black terminal giving outward motion-positive pulse.
    “+” x-over leg to mid black terminal giving outward motion-positive pulse.
    “+” x-over leg to tweeter negative terminal giving inward motion-positive pulse.
    This was confirmed in a later issue. White mentioned he preferred this arrangement after listening and testing the polarity of the system drivers with a switch and a run of speaker wire that could invert phase in the listening position.

  4. #49
    Senior Member Hoerninger's Avatar
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    Quote Originally Posted by Zilch View Post
    Article courtesy DavidF.
    Great grip back! (1989)

    Found at Prosoundweb.com:
    ... CASD ... DOS-based package from Scientific Design Software that has since been discontinued ...
    Anywhere available? (could let it run)
    ____________
    Peter

  5. #50
    Senior Member Hoerninger's Avatar
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    Quote Originally Posted by Zilch View Post
    Are White's models of the drivers good by today's standards?
    Although I'm not sure about today's standards, seriously spoken, I regard White's model as sufficient in most cases.

    He models
    - speaker resonance and
    - the voice coil specs
    as far as i have understood the article. (Simulation of cone brakeups would be very specific and are hardly to implement in a general model.)

    In a "younger" articel in Speaker Builder 3/91 by Roy Mallory, I have a German translation published in ELRAD, they are only modeling the resonance frequency by SPICE.

    Marshall Leach has investigated the influence of voice coil losses using SPICE, which is very specific and not so much known:
    http://users.ece.gatech.edu/~mleach/papers/vcinduc.pdf

    Hope this was helpful.
    ____________
    Peter

    PS: OT in this thread, but I'm wondering how the influence of a horn /waveguide can be modeled in SPICE.
    Last edited by Hoerninger; 12-12-2006 at 08:08 AM. Reason: revised

  6. #51
    Senior Señor boputnam's Avatar
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    Quote Originally Posted by DavidF View Post
    What is the translation to cone motion for the polarity scheme as shown?
    I don't see anyone having replied, so...

    If that is a 123A-1 (likely since it's the L100A...), as diagramed, the woof will move in on (+) voltage. The 123A-1 is a positive transducer, a "lone woof" back in the day, but here is (+) signal connected to BLK terminal.

    What'd I win...?
    bo

    "Indeed, not!!"

  7. #52
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    Quote Originally Posted by boputnam View Post
    Can you provide details on the set-up Dennis Murphy uses?
    When I read your post yesterday, I emailed Dennis to get some details. No answer yet.

    I do know he uses LspCAD professional (http://www.ijdata.com/products.html) for design and emulation and Praxis (http://www.libinst.com/) for measurements. LspCAD pro requires a full duplex sound card. I don't know which sound card or microphone he uses.

    When I hear from Dennis I'll pass on whatever additional info he adds.

  8. #53
    Senior Señor boputnam's Avatar
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    Quote Originally Posted by Swerd View Post
    When I hear from Dennis I'll pass on whatever additional info he adds.
    Great, thanks.

    Also ask about the physical set-up - driver and mic placement/positioning, in-doors or out, proximity, etc.

    Everyone has their little tweaks that work for them...
    bo

    "Indeed, not!!"

  9. #54
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    Quote Originally Posted by boputnam View Post
    Also ask about the physical set-up - driver and mic placement/positioning, in-doors or out, proximity, etc.
    This is what I can remember.

    All the measurements were done in-doors. So the responses below 200 Hz reflected the standing wave patterns in Dennis's workroom. He had recently moved to different house and was not real familiar with these bass patterns. This was one reason why I was initially inclined to ignore the bass peak from the ported small-volume L-100 cabinet. We thought it might be due to room response.

    The cabinet was always standing vertically on an 18" tall stand with the tweeter on top.

    The overall distance from the mic to the front baffle was more than 1 meter, perhaps as much as 2 meters, but not more than that. A lot of trial and error was done to determine mic placement relative to the drivers while making measurements. With a large 3-way speaker, just where you place the mic relative to each of the drivers makes a difference, and I don't remember what that placement was. Dennis tried a large number of locations before he was satisfied that he was getting representative sweeps.

    A listening distance of about 10' or 3 meters was assumed while designing the crossover.

  10. #55
    Senior Señor boputnam's Avatar
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    Quote Originally Posted by Swerd View Post
    A listening distance of about 10' or 3 meters was assumed while designing the crossover.
    That is a very interesting thought - it may engender some discussion here. By that I mean, in a parallel topic, many EQ their system at close-in positions - others prefer the listening position. Results certainly differ, but what matters is the result in the listening position.

    I know that using my roadgear I "tune" the response of the mains at fairly close range (out-doors) - this includes parametric EQ presets for each output (i.e., speaker element) of my tri-amp system, and then time align, same-same. When I get to the venue, I leave those output presets unchanged, and use input parametrics to tune to the venue.

    Since you are optimizing the speakers for your setting, in your case it makes sense to go the "listening position" route. I suppose mass marketing for variable / unknown listening positions demands speaker makers use closer-in measurements of the elements themselves / together, minimizing room / acoustic affects.

    Thanks for the reply. Interesting thread - and it's about L100's!!
    bo

    "Indeed, not!!"

  11. #56
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    4311

    One of my new JBL converts is starting with 4311s. Years ago I hot rodded a set with a 12 db crossover and replaced the LE25 with an 035T. I cannot find my schematic so I forwarded him your crossover design. I did find in my pile of JBL literature the tech sheet for S70 Alpha III. It had a 12db crossover typical of other L series and had almost the same components as the L-100. I was thinking this crossover might be another starting point.

  12. #57
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    Quote Originally Posted by Swerd View Post
    All the parts for two new crossovers cost me about $130. If any one is interested in a parts list, email or PM me with your email address and I'll send it to you.
    Several people have asked for this parts list along with a crossover layout diagram. I posted these on another thread located here:

    http://audioheritage.org/vbulletin/s...952#post156952

  13. #58
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    JBL polarity

    I'm sure it has been discussed many times but is there a copy of the JBL technical bulletin on polarity posted? It should be referenced whenever the 4311 or L-100s and crossovers are discussed because of the oddity of the 123A polarity. If the bulletin isn't posted I can scan it and post it.

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  15. #60
    Senior Member Russellc's Avatar
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    Quote Originally Posted by Robh3606 View Post
    There was an article in Speaker Builder??? years back where they redid the network and changed the tweeter. This is from here-say as I never saw the article myself. Could be urban legend territory

    Rob
    You are correct, I may still have that issue. I believe it was audio Amatuer back then. I'm in the middle of getting ready to move, so it will likely turn up.
    Whoops, forgot how old this post was...I see it was scanned long ago!

    Russellc

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