Vifa Xt25, Pl18 - MTM

Discussion in 'Archived Threads 2001-2004' started by Bryan_G, May 12, 2002.

  1. Bryan_G

    Bryan_G Agent

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    Hello
    I came across this design
    http://www.speakerworkshop.com/Speak...onitor%20A.htm
    These speakers look impressive. I was wondering if anybody had any experence with these speakers(vifa xt35, vifa pl18). I would appreciate some feedback from you guys on what you think this design would sound like. I am new to speaker design, and would like to start off building somebody elses design before I jump in with my own speaker.
    The xt25 looks particularly impressive. Does anybody know of any other designs(or speakers) that use this tweeter?
    Thank You
    -Bryan
     
  2. Peter Johnson

    Peter Johnson Stunt Coordinator

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    nOrh, AV Reality, Krell (10-30x the price of the other two brands) use the XT tweeter.

    Everyone seems to be of the opinion that for the $, it is exceptional.

    I have never heard it...just read a lot about it.
     
  3. Patrick Sun

    Patrick Sun Moderator
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    Bryan, check out this thread on the XT25/PL18.
    My only comments on that Speakerworkshop XT25/PL18 design is that I would advise moving the woofers closer together (it's be okay to offset the tweeter off the center line), and front port the enclosure (for maximum placement flexibility), and design for parallel connection of the woofers (not series connection) for more SPL output. I wished the author would have told us what the crossover frequency was that he used in the crossover design.
    BTW, the XT25 is on sale at Parts Express for under $55 each.
     
  4. Bryan_G

    Bryan_G Agent

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    Wow, those are some pretty impressive names using this tweeter.
    Patrick, thank you for your input. I was thinking pretty strongly about moving the woofers closer together. A parallel design would be nice. Without designing a whole new crossover I don't see how it would be possible. Did you have a certain parallel design in mind? I am trying to find out more from speakerworkshop, but I haven't got a reply yet. This tweeter looks very impressive at that price. I am ready to hear how it sounds [​IMG] .
    -Bryan
     
  5. Patrick Sun

    Patrick Sun Moderator
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    Actually, to go from series to parallel for an electrical second order (given that you know the series values), you divide the inductance by 4 and quadruple the capacitance. That's a decent starting point if you were to mess around with the existing crossover.

    Then you'd have to fiddle around with the padding resistor on the tweeter to get the levels between the woofers and tweeter to match up.
     
  6. Mark Hayenga

    Mark Hayenga Supporting Actor

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    Is the XT25 sensitive enough to match two PL18s in parallel?
     
  7. Bryan_G

    Bryan_G Agent

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    (from pe)

    The xt25

    * Power handling: 99 watts RMS/140 watts max * Nominal impedance: 4 ohms * DC resistance: 3 ohms * Frequency range: 1,500-40,000 Hz * Magnet weight: 8.5 oz. * Fs: 500 Hz * SPL: 91.5 dB 1W/1m * Dimensions: A: 4-1/8", B: 2-15/16", C: 1-13/16", D: 2-15/16".

    The pl18

    *Power handling: 100 watts RMS/140 watts max *Voice coil diameter: 1-1/2" *Voice coil inductance: .85 mH *Nominal impedance: 8 ohms *DC resistance: 5.8 ohms *Frequency response: 40-4,000 Hz *Fs: 39 Hz *SPL: 87 dB 1W/1m *Vas: .847 cu. ft. *Qms: 2.42 *Qes: .41 *Qts: .35 *Xmax: 6.0mm *Net weight: 3.75 lbs. *Dimensions: A: 7-1/4", B: 5-3/4", C: 3", D: 3-9/16", E: 1-1/8".
     
  8. Patrick Sun

    Patrick Sun Moderator
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    It'd be close. Supposedly you get a 6dB boost in SPL when you parallel 2 woofer drivers, but toss in the baffle step compensation in real world, it's more like 3-6dB, so it's worth a shot to run the woofers in parallel just to see if XT25 will run with the woofers.
     
  9. yup. sensitivity should be fine. remember..you need to have a baffle step compensation in the XO.
     
  10. Bryan_G

    Bryan_G Agent

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    I am going to try to put the enclosures together today. If everything goes smoothly I should order the drivers and crossover stuff this week. Then I should be able to play around with things a bit.
    Here is a link to the crossover he used
    http://www.speakerworkshop.com/Speak...r%20Design.htm
    I need some help coming up with a new crossover using one of those. Hopefully a simpler one.
    p.s. This forum is a great forum and all you guys are helping me out a lot. Thanks
    -Bryan
     
  11. Patrick Sun

    Patrick Sun Moderator
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    Using the guy's simple XO network, with the woofers in parallel, try:

    L2=0.94mH (some close to that value, maybe 1mH)

    C3=28uF

    On the tweeter portion, you might want to change the RZ1 anywhere from 2 ohms to 4 ohms (experiment with the padding on the tweeter with this resistor). Keep the rest of the tweeter filter as drawn up.

    This will give you a start on the XO. After this, it's up to you to tweak and play around if you're so inclined.
     
  12. Bryan_G

    Bryan_G Agent

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    Well, I got most of the parts cut out tonight, I will have to cut a few more tomorrow and try to assemble it. If I remember I will start taking pictures and show you guys how its going.

    Patrick,

    Thanks man I will have to try those values. If I moved the ports to the front what would that do to the sound? Would I need to readjust the port lengths?

    -Bryan
     
  13. Patrick Sun

    Patrick Sun Moderator
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    Nope, just get the lengths the same.
     
  14. Bryan_G

    Bryan_G Agent

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  15. Bryan_G

    Bryan_G Agent

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    Its finally coming together. I have 1 speaker together. Partsexpress sent me 1 wrong inductor so I have to wait until tomorrow to put the other speaker together. I have some photos here
    http://members12.clubphoto.com/bryan...ner-3059.phtml
    I don't know what I am going to finish them in. I'm thinking veneer or maybe black marbled Formica.
    The speaker is lacking in the bass department. I will have to add a subwoofer, but I pretty much new that would be the case. It is clear, but not quite as revealing as my akg 240df headphones. This is probably a good thing because my headphones are often times fatiguing. I can't really tell how well it images with just 1 speaker. I am going to try and make some graphs one day. That may take a while, since I haven't ever done that before. Once I get them both together I will try and do some more listening and give you guys a better feel of what they sound like.
    -brayn
     
  16. Patrick Sun

    Patrick Sun Moderator
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    Does this crossover provide baffle step compensation? That could be why you think the bass is thin (what's really happening is the midrange and tweeter frequency region is too loud compared to the bass region).
     
  17. Bryan_G

    Bryan_G Agent

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    I used the crossover in the pictures. In the article he said that the crossover induces a droop in low frequency, and that would compensate for the baffle step. However that doesn't make any sense with what you are saying.

    Do you know of any good web sites that deal with measuring frequency response? I don't really trust my ears to give me a good basis for a flat response.

    Thanks for all of your help.

    -Bryan
     
  18. Patrick Sun

    Patrick Sun Moderator
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    The hard way is to buy a SPL meter from Radio Shack (analog's cheaper, digital costs more), and then get a CD with test tones. Stryke offers a CD with 1/3 octave test tones (both sine waves, and warble tones).
    Then hook up one speaker channel up to the speaker, choose some volume level that will get you readings around 70-80dB with the SPL meter around 1 meter from the speaker. Then play the tones one at a time, and record the SPL from the meter. Do this for all of the tones from 30Hz to 20KHz.
    To see how the crossover is working, disconnect the woofer lead from the crossover, and just measure the tweeter output. Then disconnect the tweeter lead from the crossover, and connect the woofer lead back to the crossover and measure the woofer output. Put this on a graph (frequency on the X-axis, and SPL output on the Y-axis) and see what it looks like. If you find a big dip from the woofer filter kicking in too early, then you have some tinkering to do with the woofer filter. If the tweeter output is too high/loud, you may just have to bite the bullet and use the guy's original crossover design with the woofers hooked up in series (not parallel).
    It's quite a painful process. I know, I've done it countless times. It's much easier if you know someone with a speaker testing mic setup. You get the SPL output graphs in scant seconds if you know what you're doing.
     
  19. Bryan_G

    Bryan_G Agent

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    That looks like what I am going to have to do. There is alot that goes into building speakers, but I'm pretty sure this wont be my last one [​IMG] They ups guy was running late today so I got my inductor early. I will still have to wait until tomorrow to put the other speaker together though. If the local radio shack has a spl meter in stock i will probably pick one up, and do some testing tomorrow night. If I do I will keep you posted.
     

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