question on phasing issues with xovers

Discussion in 'Home Theater Projects' started by Sam A, Oct 14, 2004.

  1. Sam A

    Sam A Stunt Coordinator

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    ok so after being on this forum a while ive learned a hell of alot is the past few weeks. its teasing me to get into DIY. one question, ive seen tower speakers with 3 or 4 woofer midrangers in them. and always got confused as to how they managed the ohm values on multiple speakers and still had the phasing correct. I was thinking of getting 2 3 channel amps and using each channel for a different driver in the speaker. basically passive crossover or somethuing right? I know im missing something but want to understand the basics first.a any help?
     
  2. GrahamT

    GrahamT Supporting Actor

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    If you are going to get several amps you might as well do a digital crossover.
    I am not sure what you mean about phase. As far as I know, phase and impedance are independant. If you want to learn the basics, which aren't all that basic, pick up some speaker design books at the library.
     
  3. Sam A

    Sam A Stunt Coordinator

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    well if you have 2 equal speakers and wire them in parallel then the ohms are half and if you wire them in series then the ohms are double. but the speakers are out of phase if wired in series and are in phase if wired in parallel. so I thought to keep all the speakers in phase with each other, then you just need seperate amps for them all [​IMG]

    again, im an idiot when its about this stuff. what would a digi xover do? and would it resolve the phase issues?
     
  4. GrahamT

    GrahamT Supporting Actor

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    Dont know where you heard this, not true. Phase issues are from the reactive properties of passive crossover components (inductive and capacitive reactance). They can cause lobing and frequency response problems.

    I know very little about digital xovers, but they are very popular in the DIY crowd and apparantly do resolve some phase issues because they have no reactive components.
     
  5. Wayne A. Pflughaupt

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    It’s argued around here quit a bit how beneficial it is (or not) to use multiple amps with passive crossovers. Some people feel there is an improvement in sound quality, but that has to be weighed against the expense of using a second amp.

    As Graham noted, if you really want to use multiple amps with your speakers, the best way is to ditch the passive crossovers in favor of electronic ones. Passive crossovers rob power and they alter the sonic characteristics of the drivers they connect to.

    Regards,
    Wayne A. Pflughaupt
     
  6. Sam A

    Sam A Stunt Coordinator

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    "Sam, you’re confusing phase with polarity. But don’t feel bad – it’s a common mistake.

    Polarity has to do with the positive and negative connections of speakers being the same. If they are not, the result is that the two soundwaves are 180 degrees out of phase."

    so the end result IS out of phase, which is what I meant.

    "Typically the drivers are all wired in parallel"
    so these speakers with 4 and more drivers have driver ohm ratings @ 32+ ohms? havent seen those in a long time.
     
  7. GrahamT

    GrahamT Supporting Actor

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    Yes and no. When wiring 2 drivers in series, you always connect one of the driver's negative leads to the other driver's positive leads. They are in phase. However *If* you connect the drivers positive or negative leads together (positive to positive), they are out of phase, but there is no reason to do this when wiring in series.

    When Wayne says usually all drivers are wired in parallel, he was talking about pairs. Pairs are then placed in series for 4 woofers etc.
     
  8. Sam A

    Sam A Stunt Coordinator

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    "Yes and no. When wiring 2 drivers in series, you always connect one of the driver's negative leads to the other driver's positive leads. They are in phase"
    I thought that was out of phase, or reverse polarity meaning one moves in, one moves out.

    "However *If* you connect the drivers positive or negative leads together (positive to positive), they are out of phase, but there is no reason to do this when wiring in series."
    well thats parallel wiring anyway but they would both be moving the same direction so they would be in phase. or having the same polarity.


    "When Wayne says usually all drivers are wired in parallel, he was talking about pairs. Pairs are then placed in series for 4 woofers etc"
    so therefore the pairs of drivers will be in reverse polarity, or out of phase with other pairs they are wired in series with.


    this is just how I understand it. please explain in more detail if im wrong
     
  9. GrahamT

    GrahamT Supporting Actor

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    In series, for 2 drivers this is how you would wire them to make them the same acoustic phase:

    Positive from the amp to positive of first woofer, from the Negative of that woofer, to the positive of the second woofer. From the Negative of the second to Negative on the amp.

    On the second quote, I said if you connect the positives OR negatives together, you will be out of phase, this is still series wiring. If you connect both negatives together AND both positives together this is parallel wiring and in phase.

    I am not sure why you think certain drivers are in and out of phase. Maybe you are misinterpreting some of the terms. In series wiring, 2 drivers can be in phase or out of phase as I described above. Same with parallel, 2 drivers can be in or out of phase depending on how you wire it. Even when using parallel-series circuits they can be wired either way.
    If you have some cheap drivers around and a 9V battery, you can do some experiments yourself to see which way the drivers move. I hope this helps.
     
  10. Sam A

    Sam A Stunt Coordinator

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    "I am not sure why you think certain drivers are in and out of phase"

    huh? one driver cannot be out of phase. out of phase with what? if its reverse polarity, its just reverse not out of phase. maybe you are misunderstanding me.
     
  11. GrahamT

    GrahamT Supporting Actor

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    Yes, that is possible. But the statements Wayne and I have made are true. It is also possible for one driver to be out of phase with another. If you dont believe us try it for yourself.
     
  12. Wayne A. Pflughaupt

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    Are you referring to four or more woofers or that many drivers total?

    If they’re all woofers, they might be connected in a combination series/parallel configuration, as Graham mentioned: I.e., two pairs of 8-ohm drivers in parallel, each equaling 4-ohms. Connect the two pairs in series, you’re back to 8-ohms.

    If you’re talking about that many drivers total, it might be a tweeter, a midrange and a pair of woofers in a three-way design. A crossover can easily be designed to handle either as 4- or 8-ohm drivers, or a combination of the two. As mentioned, often resistors are employed in the crossover to accomplish desired system impedance at the binding post.

    Case in point: I used to have some home speakers that were 8-ohm two-way with a 10” woofer. Since they were sitting around doing nothing, I decided to throw them in my car as make-do subs. The tweeters and woofers were 4-ohms at their voice coils, so I figured that taking out the tweeter would get me a 4-ohm cabinet. Didn’t happen: I took out the tweeters and was still getting an 8-ohm reading at the binding posts, courtesy of the passive crossover that was still in place.

    Also consider than what may appear to be four woofers might not actually be all woofers. For instance, so-called “two-a-half-way” designs are pretty popular now, and they typically use identical-sized woofers. In the case of four such woofers being utilized in a two-and-a-half design, one pair will run full-range from the tweeter’s crossover point, while the second pair will low pass at maybe 100-200Hz. The result is that two drivers are carrying the mids, and all four carry the bass. Each pair could be 8-ohm drivers connected in parallel to separate sections of the crossover.

    Hope this helps.

    Regards,
    Wayne A. Pflughaupt
     
  13. Sam A

    Sam A Stunt Coordinator

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    "is also possible for one driver to be out of phase with another." if you read what I typed, I never said it couldnt. im just curious as to how they get 8 ohm values from like 4 woofers and a tweeter while keeping all the drivers in equal polarity or in phase with each other using one amp rated at 8 ohms instead of using multiple channels rated at 8 ohms
     
  14. Patrick Sun

    Patrick Sun Moderator
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    It depends on the woofer drivers used impedance-wise.

    For this concrete example, 4 woofers. If each woofer is rated with a nominal impedance of 8 ohms, then what Wayne offered is how it's accomplished:

    2 woofers are paralleled for a combined nominal impedance of 4 ohms.

    The other 2 woofers are also paralleled for a combined nominal impedance of 4 ohms.

    With 2 sets of paralleled woofers each acting like a 4 ohm load, to get 8 ohms nominally, you simply connect each set in a serial fashion.
     
  15. Sam A

    Sam A Stunt Coordinator

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    ok, my next question is, would it be better to leave the speakers playing full range on seperate amp channels than to xover them because they are on the same channel?
     
  16. Patrick Sun

    Patrick Sun Moderator
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    I think you're making this more complicated than it has to be. I don't follow your question.
     
  17. Sam A

    Sam A Stunt Coordinator

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    basically, which is better, multiple drivers at their full range on seperate amps or multiple drivers off one channel x'dover?

    do i make this clear? im wondering why theri arent more multiple channel speakers out there?
     
  18. Patrick Sun

    Patrick Sun Moderator
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    I think you're asking if it's better to bi-amp the drivers within a speaker (you wouldn't want to just use amps to drive the drivers full-range because you want the integration of tweeter/woofers to produce a smooth frequency response curve so the speaker sound good). Running the drivers full-range for both tweeters and woofers will usually produce a hump in the midrange that wouldn't sound good in the long run.

    Bi-amping different parts of the speaker, with the filters that cross over the frequencies to the different driver sections, is purely a user's prerogative, some like it, some think it's a waste of money to double up on the amps when it's not really needed or produces negligible benefits.
     
  19. Sam A

    Sam A Stunt Coordinator

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    then can you please explain line array speakers and how all that works if the drivers arent full range. and are all the drivers in phase with each other. ive read somewhere half of the speakers are out of phase on those.
     
  20. Patrick Sun

    Patrick Sun Moderator
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