Need X-over Design Help

Discussion in 'Archived Threads 2001-2004' started by Mike_Seerden, Feb 25, 2002.

  1. Mike_Seerden

    Mike_Seerden Extra

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    I am planning on building bookshelf monitors for L/C/R and surrounds all the same. I wanted to use the new VIFA XT25TG-30 1" Dual Concentric dome tweeter and the VIFA M18W0-09-08 6.5" woofer. I would like to build a sealed box as I am using a nice Tempest sub to fill in the low end. I need some suggestions on choosing a crossover design or trying to figure one out. Norh uses these drivers in the Prism line but I can guess they wouldn't tell me their x-over design. Is there software available to help design one.

    Another option that probably would be out of my budget for now but an interesting design. Purchase 5 premium 2 way active x-overs (Audio Control or RANE perhaps). 2 ATI 1505 or other nice 5 channel amps. An Outlaw 950 pre/pro to run the amps when available. Run the tweets and woofer on seperate amps kind of like a pro sound setup. This would certainly take out the interactions that a passive x-over has on drivers and how the network effects the drivers sound and dispersion. What do you all think?
     
  2. Patrick Sun

    Patrick Sun Moderator
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    The problem with that combo of drivers is that the XT25 tweeter doesn't like being crossed over low (under 2.5KHz with a series XO, or probably over 3KHz with a parallel XO), and the M18 doesn't like being crossed over high (over 2KHz), so you might left with either hole in the midrange, or some raggedness if you cross the woofer high.
    I would suggest posting this question over on the Madisound Discussion Board for more in-depth attention to your question.
    But, there's is an AR webpage that's almost dedicated to fine-tuning series XOs.
    There's also one project that's close to your needs that's called "The Nebula" which can be access if you have a Yahoo account. The only difference is that instead of the Vifa M18, Ken Perkins uses the Vifa PL18 for the woofer. Ken's a good guy (actually met him in in October of last year at a DIY meet) and really dedicated to fine-tuning XOs. Ken used the AR series XO concept to solve some shortcomings of the XT25 to get it to perform correctly and to fix a resonance peak to get a relatively smooth impedance curve for the The Nebula.
     
  3. Mark Krawiec

    Mark Krawiec Agent

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    hey patrick,

    do you have any links- i searched the madisound board and couldn't find a thread where the xt25 doesn't like xovers lower than 2.5-3k. that's somewhat puzzling looking at fs and the response curve of this driver

    mark
     
  4. Patrick Sun

    Patrick Sun Moderator
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    Mark, this is just from reading Madisound and the PartsExpress Tech board. Post a question at the PE board and you'll get some responses for the optimal XO frequency for the XT25, and it's not super low like 2KHz or under (people tried various resonance traps for it, but it was not until people started using series XOs for the XT25 that they were happy with its performance, which has been described as colorless, transparent, and a bit dry - never calls attention to itself).
    I remember following the discussion on this new tweeter when it was all the rage because, well, it's got that mesmerizing nipple phase plug thing going for it. [​IMG]
    Don't always assume a low resonance frequency means it'll preform well when it is crossed over at 2 times its resonance frequency.
    This is why you don't see to many people racing to use this with 2-way systems, the more commonly held wisdom for this driver is for use in 3-way systems due to its optimal XO frequency in the 2.5-3KHz range or higher.
     
  5. Mark Krawiec

    Mark Krawiec Agent

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    thanks patrick
    there does seem to be quite a bit more at the pe board regarding this tweeter[​IMG]
     
  6. Dave Poehlman

    Dave Poehlman Producer

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    Mark, let us know how you solve your problem. I like the look of that Vifa tweeter.
     
  7. Mark Krawiec

    Mark Krawiec Agent

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    well, i'm not so sure i'm going to get one of these.
    for my current project i'm looking for drivers with fairly low fs (~500 give or take) that i can cross over fairly low. it's kind of a drag to have to buy a driver, then find out after testing it, that it really won't work. still, it's a very cool looking driver (i mean i know it's the sound, but a little visual appeal never hurt[​IMG] )
    on the other hand, if any of you around sacramento want to buy a couple and we'll drag my clio setup out (if i ever get it from old colony!!) and play with them, i'm game.
     
  8. Mike_Seerden

    Mike_Seerden Extra

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    Thanks all for your help. I am just in the planning stages so have not committed to buying a particular woofer. Perhaps I will look for a 5.25" driver instead that would be more comfortable crossing over 2.5K to 3K. I will dig through the forums you guys suggested and see if I can find a better match.

    What about using active cross overs? Anybody doing it? I would only need 3 units as they come stereo so that is better than five I was thinking. Wouldn't the sound coming out of the drivers be less tarnished by any x-over network? I would think the driver would just reproduce it's range without any ill side effects. Let me know what you think.

    Mike
     
  9. Patrick Sun

    Patrick Sun Moderator
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    Mike, if you're married to the XT25, why not just use the Vifa PL18's in Ken Perkins's design of "The Nebula"? The guy's a tweaking maniac, so when he's happy with a XO, I'm confident it'll do the job for you.

    I'm not into active XO's because I'm not too keen on having to worry about external power supplies for active XO's in conjunction with the speakers. But that's just personal preference.

    The thing about XO design is that you have to treat everything (the drivers, the XO, the enclosure, the stuffing, the porting, etc) as one big system, and you can't just rely on the XO to just cut out unwanted frequency regions because you have to also consider the effect on the total system impedance by the XO and drivers, plus the phase response (and time aligning the drivers so your ears hear both drivers in sync with the music/voices), and the low end response (the F3 of the enclosure/response) and baffle step compensation to thicken up the bass under 500Hz.

    I wish I had the nice testing gear and XO software, it makes iterating to a good XO a much less taxing process.

    Madisound also offers a LEAP XO design service (as long as you use drivers that they sell) for $60/design, and you can specify the dimensions of the baffle (they'll suggest final internal volume which helps in determine the depth of the box) and they'll apply it to the LEAP design parameters. The design will get you within 90% of the most optimal XO design, so if you don't have the testing gear or software, it's not a bad deal or start.
     
  10. Ryan Schnacke

    Ryan Schnacke Supporting Actor

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    If you're still considering active crossovers check out this link
    www.t-linespeakers.org/pomann/crossover.htm
    I just recently found this. Haven't ordered anything from the guy. And really I haven't tried his Excel crossover component calculator. But I've read most of his pages and its good stuff.
    Seems like a DIY active crossover would be perfect for your project. Try one xover design and if you don't like it, just try another one - different frequency, different order. Going active makes these changes easy - cheap components, breadboard for experimenting, cookbook style design.
     
  11. Mike_Seerden

    Mike_Seerden Extra

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    Your right Patrick, the Nebula looks good. Don't want to reinvent the wheel.

    That active thing looks interesting Ryan. Thanks
     

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