Can someone explain "phase" to me?

Discussion in 'Archived Threads 2001-2004' started by tom_furman, Sep 29, 2002.

  1. tom_furman

    tom_furman Stunt Coordinator

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    I'm setting up my new 225l tempest and I've been eyeing the Phase knob on the amp. What exactly does it do? any links/info would be appreciated! thanks, tom
     
  2. Mark Fitzsimmons

    Mark Fitzsimmons Supporting Actor

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    Have you ever studied trig? Because, most simply, sound is nothing but a bunch of sine curves. All the phase does, is translate the sine curve generated by your amp by a certain amount. All it does is adjust the phase shift. This allows you to better blend your sub with your mains.

    The best way to set your phase is to play a tone at your crossover frequency and adjust the phase until SPL is maximized.

    Thats my take on it, maybe someone else will be able to explain it simpler if you don't understand me.
     
  3. Chris Tsutsui

    Chris Tsutsui Screenwriter

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    It's easier to understand phase when you understand the physics behind it. Check out the FAQ in the hardware archives as well.
    The effect the phase knob has is at the crossover frequency where the mains and subwoofer overlap. This is because the mains produce (ie 80hz) in addition to the sub producing 80hz causing an overlap. Both speakers are playing the same frequency so what happens is those frequencies can either cancel eachother out, or reinforce eachother.
    Phase control adjusts how much of the 80hz you want to hear. You can adjust phase so the crossover frequencies are loudest by doing what Mark said, or adjust the phase so the crossover region is quietest by doing the opposite.
    I think it's best to adust phase so there's no spike or dip at the crossover point. So depending on the room interactions and listening position, the phase adjustment may vary.
    The difference phase has on my room and listening position can have a difference in loudness up to 6 decibels from 0 degrees phase to 180 deg. This is why I think of phase as more of a fine tuning measure that allows users to adjust the 80hz (or crossover) region similar to how an equializer can.
    Come to think about it, it's basically like a one band equalizer at the crossover point between sub and mains.
     
  4. tom_furman

    tom_furman Stunt Coordinator

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    Thanks guys! That helps...whether or not i'll ever be able to tell the difference when i adjust the knob is another question [​IMG] i must have the most tone-deaf ears in the world when it comes it speakers/subs.
    Now...i'm gonna put the sub into it's normal "spot" in my room. Smack dab between the wall and the bureau that my Tv sits on. Will this make the sun sound like crap? Being so smooshed in between objects? I thought with bass it was better if u can put it near a corner/wall right? its ALOT of moving so i want to make sure i'm not gonna have to move it back right away.
     
  5. Mark Fitzsimmons

    Mark Fitzsimmons Supporting Actor

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    The best way to test where the sub will sound best is to put the sub at the listening position, and then crawl (yes, crawl) around the floor of the room until the bass sounds the best to your ears. Once you found that spot, put the sub there.

    I know its alot of moving, I own a DIY Tempest myself, not quite as large as yours but huge none the less. It is a pain to move, but once its in place you should be done.
     
  6. Chris Tsutsui

    Chris Tsutsui Screenwriter

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    BTW, you can be tone deaf and still tune phase because you just have to be able to tell the difference in volume levels. [​IMG]
    Here's my opinion on the crawl tuning.
    By placing a sub on the ground at the listening position, I do not believe it is necessary to have to crawl on the ground. The only reason to crawl instead of stand would be to hear the effects the height of the room has on bass...
    So, what you "should" do is prop the subwoofer in the listening position so that the driver is also at the listening head height, and then crawl with your head at the height of the subwoofer when it's laying on the ground.
    You are basically swapping your head with the drivers position.
    If you don't do it that way I see no immediate benefits from crawling on the ground and having a sub on the ground as well. It would kinda be like calibrating your sub with the mic on the ground.
    In other words, I wouldn't crawl on the ground to tune if the subwoofer is also on the ground.
    Does this make sense?
     
  7. Wes

    Wes Screenwriter

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    Or you could put a good bass song on the CD player have a seat on your nice comfy cozy couch and have the wife adjust the Phase knob, and when your smile is the biggest then thats the correct setting!
    No crawling or lifting of heavy objects![​IMG]
    Wes
     
  8. Mark Fitzsimmons

    Mark Fitzsimmons Supporting Actor

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  9. BruceD

    BruceD Screenwriter

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    A little more explaining about phase and subs:

    If the actual sub driver cone is pushing out while the main speaker driver cone is pushing in, the two speakers are essentially 180 degrees out of phase and will tend to cancel each others output (in other words the bass frequency both are trying to output is reduced).

    On the other hand if both the cone drivers on the sub and main speakers are synchronized (pushing out together), then the bass output is increased.

    How closely the two cones follow each other (or don't) in the time domain is indicated by phase degrees (0-360 degrees).

    Typically the above is true if the sub and main speakers are 6 feet or closer from each other. Things are not as simple when they are farther apart.
     

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