Phase shift

Discussion in 'Archived Threads 2001-2004' started by Troy_j, Dec 8, 2002.

  1. Troy_j

    Troy_j Agent

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    Isn't it true that a 180 pase shift will be introduced if you wire a speaker + to- the amp + to +. I'm wondeing about a way to introduce phase shifting into a n amp that isn't set-up for it. Also how inportant is it anyway?

    Thanks am planning on driving a Tempest with a mono carver m1.0t.
     
  2. ThomasW

    ThomasW Cinematographer

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    Depends on the phase relationship between the amp and the speakers.....

    If 'in-phase' wiring is amp +/- to speaker +/-, then 180 degrees out of phase is amp +/- to speaker -/+

    It's important to have the sub in-phase with the mains because if they aren't, the frequencies that overlap will be cancelling each other =less bass.

    A quick and easy way to check phase is to play something with a fair amount of bass energy. Using one hand gently place your finger tips on the edge of sub surround. Place the other hand on the edge of the surround of one of the mains. If they are moving in and out at the same time the speakers are in-phase
     
  3. Dave Milne

    Dave Milne Supporting Actor

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  4. Troy_j

    Troy_j Agent

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    What I meant was Red binding post speaker wire from receiver, going to the red binding post on the driver. E.g. red to red, and black to black, for say the left channel; that would normal, and " in phase." And conversely if the red binding post from the receiver wire going to the black binding post of the driver; would be 180 out of phase. I hope I'm making sense, and also this is for only one channel:b
    Just Taken from:
    www.hifi.com/store/category.cgi?category=hookup_connection_gen
     
  5. Dave Milne

    Dave Milne Supporting Actor

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    Troy,
    I thought that might have been your intent. And you're right, connecting the red amp terminal to black speaker terminal will put it 180 out of phase.

    As to which connection is best for your system... that's a bit more complex. Phase angle is a "moving target" because of the phase shifts introduced by the crossovers and the speakers themselves. About the best you can do is try to pick the closest phase match at the crossover frequency and hope that it doesn't deviate too much in the "overlap region". For example, the second-order, 80 Hz "THX standard" crossovers are only down 12dB an octave on either side (40Hz to 160Hz).

    The simplest way to select proper polarity is to play a test tone at the crossover frequency through the system. The subwoofer polarity that yields the highest level at the listening position is generally best. A better approach is to measure the frequency response of the system (from the listening position) with both polarities and select the flattest one.

    Finally, with all due respect Thomas, I can't imagine that your fingers are sensitive enough to tell if drivers are moving in or out at any usable frequency. I wouldn't trust any of my body parts to differentiate 6 ms (half-wavelength at 80 Hz).
     
  6. ThomasW

    ThomasW Cinematographer

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  7. Troy_j

    Troy_j Agent

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    Thomas,and Dave Thank you both. Each of your responces shed light on my question, and I appriciate it. I never did understand why my parents amp had a " phase" dial............[​IMG]
     

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