Crossover ???

Discussion in 'Home Theater Projects' started by John Titan, Feb 21, 2006.

  1. John Titan

    John Titan Stunt Coordinator

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    Hi

    I have a question for you more advanced DIY guys.

    I have an older set of Yamaha floor speakers (model# NS-A570) 3-way w/12" woofer. Rated at 140 watt max into 8 ohms. Box Size is about 2.5 cubic foot. The tweeter and midrange look to be 2-1/2" and 3-1/2".

    The tweeter is using a 5 watt 7.5 ohm resistor and a Luxon 3.3 uf cap. Wired straight trough to the terminal cup (same as below)

    The midrange uses a 5 watt 6.8 ohm resistor and a Luxon 4.7uf cap. (both caps also say 5.0mv NP)

    The woofer has nothing on it.

    All 3 drivers have separate wires connected at the terminal cup.

    A few Questions
    What are the crossover points for the tweeter and midrange? ( I haven't been able to figure this out with the resistors in the mix)
    What ohm woofer would I use 4,8,16? I purchase a set of these http://www.partsexpress.com/pe/showd...number=290-335
    And while they do sound a little cleaner than the original ones they do lack some of the bass.( the old ones were dry rotted, and I needed a cheap replacement) Should I have gone with 4 or 16 ohm rather than the 8? I know the box volume is a little to low for this model but it seem to fit the best of the cheaper ones they sell. Will break-in
    help at all. They have much stiffer cones. Any help is appreciated.
     
  2. Dave Poehlman

    Dave Poehlman Producer

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    Any idea of the impedence rating of the original drivers?

    The driver you've selected has a pretty high total Q (Qts) meaning it has a stiff suspension. Probably why you're hearing less bass out of it.

    As far as the "crossover" goes... it sounds to me that the caps are there mainly to keep the smaller drivers from being damaged by low frequencies and the manufacturer is depending on the natural rolloff of the midrange and woofer to act as the crossover. The resistors are probably there to damp the drivers a little bit. I wouldn't expect there's much correlation between their values and what the drivers are capable of. A lot of big box retail speakers are like this. In a nutshell, it's a cheap way to build a speaker.

    If you can get impedence values for the midrange and the tweeter, I'd bet you could put together a cheap 3-way crossover that would make a world of difference IMO.
     
  3. John Titan

    John Titan Stunt Coordinator

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    They don't have anything on them. Is there anyway I can test them with a multi-meter.

    What about these:
    3-way crossover

    Or did you mean designing my own (this right now is beyond my scope). I can solder and I been trying to learn as much about speaker building and crossovers as I can but it's difficult to grasp at this point for me. ( I think I'm trying to learn to much at once!)

    Thanks for the help
     
  4. Dave Poehlman

    Dave Poehlman Producer

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    The crossover will help with overall clarity IMO. Right now, you're getting a lot of overlap and probably a lot of breakup from the mid and woofer.

    Wiring a 3 way for a first crossover might be a little daunting... and buying individual components can rack up in cost pretty quick. And, from the sound of it, you're not looking to invest a lot of cash here.

    Your bass issue is something related to the woofer you're using. Are your enclosures ported? If so, what size are they? (diameter/length) You might be able to tweak the port size/length to give you a little more bass.
     
  5. John Titan

    John Titan Stunt Coordinator

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    They're sealed with fiberglass dampening just on the back wall. 40'h x 14'w x 8.5d Outside measurement.

    I actually sent the woofers back to PE. I Didn't want to waste to much time trying to get them to work. I don't mind spending the money if there going to better the performance. When I used PE's woofer selection wizard this is the only one that came up ( I had to up the box size a little to even get a match, think I put in 3.25 cubic feet)
    I've heard that you can use a woofer made for a little bigger box size as long as you dampen the box.( not sure if I'm wrong on that) That's why I chose that one.

    As far as the crossover goes I'm pretty sure on my ability to physically make it. But designing it is what I can't do at this point.

    I would love to replace ALL the components and build a crossover for them, but to do it right I know you'd need some test equipment. But I would imagine most people would probably suggest I just build someone else's design from the ground up and not bother trying to work around the box size i've got.

    I know Madisound will design a crossover using there Leap modeling program for about 40$, but is it worth it?

    I just don't want to waste money for something that just isn't worth it.
     
  6. Brent_S

    Brent_S Second Unit

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    If you were satisfied with the Yamaha's sound, you could use one of the PE kits to replace the woofer surrounds, if that's the part that was damaged.

    Most likely, a LEAP designed xover will sound pretty decent. One that's been further tweaked by hand, like most of the published DIY projects or packaged kits, will sound even better. To design with your existing drivers, Madisound would need the T/S parameters, which they probably don't have access to either.

    If you're trying to reuse the cabinet, you could possibly find a published design that would work in your cabinet volume. You can make the cabinet "smaller", if needed, by placing solid material in it.


    wbs
     
  7. Dave Poehlman

    Dave Poehlman Producer

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    Here's where you start getting into subjective opinions about audio and what you're looking to get out of this project.

    Personally, I do DIY for the cost savings. I look for sale drivers, I work off factory specs, I keep my crossovers simple. If I can get them to sound nice for low cost, I'm happy.

    Others here are willing to pay a little more attention to detail and invest more time and money looking for that perfect response curve... and there's nothing wrong with that either.

    So to answer your question, is it worth it? It's up to you.

    If it were me... I might pick up a pair of THESE since they look like they'd be happy in a 2.5 cuft box. And, since nothing is really known about the mid or the tweeter, I'd just use the pre-fab crossover you mentioned earlier and call it a day. But, again it's entirely up to you.
     
  8. John Titan

    John Titan Stunt Coordinator

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    I was actually thinking about those Dayton's as well. Maybe I'll give them a try with the X-over and see.

    Worst case I'll send them back and be out a little money on shipping. These are cheap speakers to begin with so a decent woofer and x-over may make big difference.

    Thanks for the help guy's.
     
  9. Dave Poehlman

    Dave Poehlman Producer

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    Let us know how they turn out.
     
  10. John Titan

    John Titan Stunt Coordinator

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    Will do!
     
  11. christianCA

    christianCA Auditioning

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    [​IMG]
     

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