Subs phase alignment

Discussion in 'Official REW (Room EQ Wizard) Support Forum' started by Jaromir Mikes, Aug 7, 2017.

  1. Jaromir Mikes

    Jaromir Mikes New Member
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    Hi,

    what i would like to do is phase alignment of my subs to main speakers with using REW.
    Is anywhere some tutorial or how-to?
    What I have tried to do was - to measure my subs and main speakers and compare phases of both in "overlay" window.
    I was expecting changing delay on main speakers would shift the phase of main speakers, but it doesn't :(
    Any help?

    best regards

    mira
     
  2. jtalden

    jtalden Member

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    There is no easy step by step path that I have seen that reliability arrives at the best solution for phase tracking. One problem is that the SW to mains XO range falls into the room mode range of frequencies. This plays havoc with the phase at the LP. The best solution often requires an investigation of the XO frequency and delay/distance settings. It takes practice to find the best compromise solution in many cases. The other setup methods for XO timing may have equally favorable results and tend to be easier to explain.

    That said, I have experience in using this method and, given the proper measurements, can provide the best timing solution for a particular XO setting. You could use that finding to set your timing, or to confirm the results of another method. Most all the automated setup features provided in AVRs now will make the distance settings automatically. These often provide a very good solution, but can have similar difficulty with particular situations.

    If you want my recommendation for timing, please advise me your audio equipment and basic setup situation; I also need to know the mic and soundcard that is being used. I can then provide detail on the measurements that will be needed for my analysis.
     
  3. Jaromir Mikes

    Jaromir Mikes New Member
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    Hi,

    meanwhile I have found this article:
    http://www.hometheatershack.com/forums/rew-forum/28894-case-study-sub-alignment-using-rew-v5.html
    I am basically understand and agree that this problem is related only to frequencies close around XO freq.
    Frequencies which are reproduced by both subs and main speakers too.

    I am not using "home theater" system but rather would like to use this method on larger musical systems (concerts)
    where main PA is flown and subs are stacked on ground.
    I usually adjust delay on subs or main PA based on distance measurement using laser tool.
    I have focusrite 2i2 sound card and borrowed klark teknik measurement mic.

    I am searching for some time effective method as I am not working with one fixed installation,
    and system tune is only small part of my job which has to be done during a day ;)

    I know there pro SW like Smaart or Systune which should be able to help with this issue but they are too expensive for me
    and phase alignment is feature I would use them for.

    mira
     
  4. jtalden

    jtalden Member

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    There several other threads there where I have helped determine the best delay timing based on phase tracking analysis. A review of those may be all your need to gain enough info to understand the process. A search for 'phase tracking' and my user name should work reasonably well.

    Your situation may be easier than small rooms with less modes in the XO range, but I have no experience with those situations. I am not in a position to write up a detailed step by step at this time, but can answer a few a questions, confirm one of your setups, or find the proper timing for an example setup if given the proper measurements.
     
  5. Wayne A. Pflughaupt

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    I’m not sure there is an easy way to do this. Assuming the subs are roughly directly below the mains, the problem is that people in the front seats are closer to the subs than they are to the mains overhead, while people further back are closer to equidistance between the two (assuming a large enough auditorium).

    You might get some relevant advice from the permanent installations section at the ProSoundWeb Forum.

    Regards,
    Wayne
     
  6. MasterLufier

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    First time, when we talk about big venue (not personal music listening room), we need find a mic position. Second part of this guide is very useful. Usually, i'm use "Method B", so it's make longer throw, much powerful and better coverage. And when you set mic position (typically it's so far from PA and it's must be on axis of one of you PA, left or right) you will need move you mic on soft foam or something else, like this. This method will help you capture fidelity phase response, without shifting from floor reflection on low frequency (usually, up to 1-2kHz).

    Ok, and now You can start measure. First time mute all you other PA side, all you subs, infill's, outfill's and center cluster and make top IR. And after mute top and unmute sub only on same side. And you will have something like my screenshot.
    K2.jpg SB28.jpg
    After this go to TOP impulse and click "Estimate IR delay". Remember shift time from popup window, go to SUB impulse window, and insert to "t=0 offset, ms" exactly the same time. Open Overlays window and go to phase. For much convenience I'm move window, like a screenshot.
    Снимок экрана от 2017-09-07 23-37-28.png
    Ok. And you will set cursor on overlays window on position, where phase angle (not a phase crossing, it's very important) of all measures maximum same. On my screenshot it's 100Hz. After, You will get sum phase angle on your calculator, without minus, if it have. On my trace it's 45+119 = 164. And after you will find which delay get phase shift your sum on your frequency on formula t(ms)=(Ph/(360*f))*1000. (For me it (164/(360x100))*1000 = 4.555ms
    And now you can insert this value to "t=0 offset, ms" on TOP impulse (but TOP phase is much flat, than SUB), you need add minus. See my next screenshot.
    Снимок экрана от 2017-09-08 00-02-33.png
    And if you loudspeaker processor have All Pass filter, you can set phase some better. this good for highest SPL, but not good for IR.
    Снимок экрана от 2017-09-08 00-19-21.png
    Sorry for my English, but i hope, i can help. Best regards, Mike.

    p's This is not a classic SUB+TOP alignment, so PA is L'acoustics K2 and subs SB28. K2 is fullrange system, and have more overlap with sub, but on normal SUB+TOP system you will need same. And sub's had flown, at 2 meters on rear top's
    20901396_1800033913370636_1504868348515152473_o.jpg
     
    #6 MasterLufier, Sep 7, 2017
    Last edited: Sep 7, 2017

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