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Thread: How-To: Verify Phase Cohesion Through A Crossover

  1. Back To Top    #21

    Re: How-To: Verify Phase Cohesion Through A Crossover

    Quote Originally Posted by Cathul View Post
    Thanks for that tip. Just verified that the curves match, and they do.
    Guess my wife will hate me next week.
    On the other hand i don't really know if i need/want to do it over again as the system measures and sounds good right now.
    So i don't really know if i want to do it again just for the sake of getting rid of a phase flip.
    Don't kid yourself - you know you're going to do it over again. :-) I have a feeling that you are similar to me, in that the phase flip will continue to "bother" you until you "fix" it. Even though the end result would most likely be the same... It's just the way we're "wired" (pun intended). ;-)

    What's funny is that I recently changed all of my front stage speakers and have been re-tuning - and I couldn't figure out why my crossovers weren't lining up correctly. Here it's because I forgot about REW using some other crossover type for "Subwoofer" and "Bass Limited"! So I just made the exact same mistake even though I already knew about it! You post made a light-bulb go on and I realized what was wrong. :-) So thanks for bringing it up!

  2. Back To Top    #22
    Noob Cathul's Avatar
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    Re: How-To: Verify Phase Cohesion Through A Crossover

    Thing is... the overall response is better than it ever was when using the driver specific curves from the spreadsheet (sorry Jazzi). It‘s most probably user error in regards to tuning after the curves, but this time after flipping the phase it matched perfectly without the need to change the eq in the xover region, unlike before.

    But yes, someday next week I’ll do everything again on a different preset.
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    Re: How-To: Verify Phase Cohesion Through A Crossover

    I learned this from Andy Wehmeyer who goes into this exact same thing in his blogs and tutorials but Nick does an excellent job explaining it with REW and using examples. Nice job man.
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  4. Back To Top    #24

    Re: How-To: Verify Phase Cohesion Through A Crossover

    Holy crap dude, thanks for the vid. This made a unbelieveable difference for me retuning my system, took me awhile to figure the all pass stuff out but wow what a difference it made.

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    Re: How-To: Verify Phase Cohesion Through A Crossover

    Quote Originally Posted by jtrosky View Post
    Don't kid yourself - you know you're going to do it over again. :-) I have a feeling that you are similar to me, in that the phase flip will continue to "bother" you until you "fix" it. Even though the end result would most likely be the same... It's just the way we're "wired" (pun intended). ;-)

    What's funny is that I recently changed all of my front stage speakers and have been re-tuning - and I couldn't figure out why my crossovers weren't lining up correctly. Here it's because I forgot about REW using some other crossover type for "Subwoofer" and "Bass Limited"! So I just made the exact same mistake even though I already knew about it! You post made a light-bulb go on and I realized what was wrong. :-) So thanks for bringing it up!
    Redid it today on another preset with Jazzis spreadsheet.
    For whatever reason i cannot get the midbass and tweeters sum up to 6db where when i use "subwoofer" in REW for the slopes it sums perfectly.
    See for yourself.

    Click image for larger version. 

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    First is with choosing "subwoofer" in REW for the slopes and phase flip and second is with Jazzis spreadsheet without the phase flip.
    Distances (from tape measure) are the same, electrical crossovers are the same.
    First one is with sub, while i left out the sub in the second shot.
    And yes, first one is only 3-4 DB summation, but sums flat, while the LR24db slopes also only add up to 3-4 db, but i cannot reach the target curve.
    With Jazzis curves i fiddled with the delay of the tweeter on both sides, i.e. in 0.02 ms steps and remeasured after each step, but that was the best i could achieve. When i flipped the phase on the tweeter i got a huge dip with Jazzis curves as expected.
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  6. Back To Top    #26

    Re: How-To: Verify Phase Cohesion Through A Crossover

    Quote Originally Posted by Cathul View Post
    Redid it today on another preset with Jazzis spreadsheet.
    For whatever reason i cannot get the midbass and tweeters sum up to 6db where when i use "subwoofer" in REW for the slopes it sums perfectly.
    See for yourself.

    First is with choosing "subwoofer" in REW for the slopes and phase flip and second is with Jazzis spreadsheet without the phase flip.
    Distances (from tape measure) are the same, electrical crossovers are the same.
    First one is with sub, while i left out the sub in the second shot.
    And yes, first one is only 3-4 DB summation, but sums flat, while the LR24db slopes also only add up to 3-4 db, but i cannot reach the target curve.
    With Jazzis curves i fiddled with the delay of the tweeter on both sides, i.e. in 0.02 ms steps and remeasured after each step, but that was the best i could achieve. When i flipped the phase on the tweeter i got a huge dip with Jazzis curves as expected.
    Well, either way, you are only getting 3-4dB of summation at the crossover, which I believe is the actual problem. The difference is just that REW uses 24dB Butterworth crossovers when selecting "Subwoofer" - which I believe would normally (if you had full summation) have a "bump" at the crossover point. In your case, the butterworth crossover is coming out "flat", when it really should result in a "bump".

    So you do not appear to be getting full summation at the crossover for whatever reason.

    Have you ever measured L+R speaker "pairs"? For example, left+right tweeters and left+right midbass? In my case, when I play L+R speaker pairs, the resulting "shape" of the response is slightly different that the individual speaker measurements. I have a few dips (one wide and one narrow) in my midbass L+R pair response that don't exist when I measure the speakers individually.

    I'll post some examples shortly. These dips don't seem to be phase-related - applying an allpass filter like Nick shows in the video has absolutely no effect whatsoever on these dips. Maybe the are reflection-related? They do respond normally to EQ, so I can easily apply an EQ filter to "fix" it - although, I'm not really sure if I even should fix it.... Again, will post some example pictures shortly (I'm not experiencing a nice flat summation at the crossovers either, so the post will also be on-topic).

  7. Back To Top    #27
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    Re: How-To: Verify Phase Cohesion Through A Crossover

    Well, i'm still fiddling with EQ and time alignment, and yes, my wife is looking angry at me whenever i go back to the car.
    Looks a bit better than before as the lowpass on both midbasses were not exactly where i wanted them to be. Same for the highpass of the tweeters.
    Now i get 4-5 db summing for both left+right which looks a lot better.
    Bass is spot on in the xover region though.
    Still have to measure them in pairs, but now i got to work first.

    It really sounds good now though, but it always could be better, right?
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  8. Back To Top    #28
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    Re: How-To: Verify Phase Cohesion Through A Crossover

    Well, i'm still fiddling with EQ and time alignment, and yes, my wife is looking angry at me whenever i go back to the car.
    Looks a bit better than before as the lowpass on both midbasses were not exactly where i wanted them to be. Same for the highpass of the tweeters.
    Now i get 4-5 db summing for both left+right which looks a lot better.
    Bass is spot on in the xover region though.
    Have to sill measure them in pairs, but now i got to work first.

    It really sounds good now though, but it always could be better, right?

    Click image for larger version. 

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    edit: nevermind... fucked up the slopes while dealing with the EQ. Am narrowing to a 4th order butterworth again.

    How do i deal with something like this if my DSP doesn't have allpass filters?
    F.e. the sub/mid integration if it's only summing up to 3 db with a LR24db alignment. Add time on midbass/tweeter until it matches? Maybe in 0.4ms increments (if 360° phase is 12.5 ms at 80Hz --> 11,25° would be ~0.4ms) and when it gets better do finer adjustments?
    Any tips?
    Last edited by Cathul; 05-18-2020 at 10:25 AM.
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  9. Back To Top    #29
    Wave Shepherd - aka Jazzi Justin Zazzi's Avatar
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    Re: How-To: Verify Phase Cohesion Through A Crossover

    Can you share a screenshot of the names of the target curve files you are using from my spreadsheet? That might help.

    Can you also share a screenshot of the equalizer settings within REW? Like the one below:

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    I overlaid them to see the difference. The one with the wider and more shallow gap between speakers has a poor summation.


    Click image for larger version. 

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  10. Back To Top    #30
    Noob Cathul's Avatar
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    Re: How-To: Verify Phase Cohesion Through A Crossover

    It's the same custom overall curve for both. Made a custom curve as both whitledge and half of whitledge didn't fit my taste in my Mustang.
    Whitledge had way too much bass and and not enough treble for my liking and half of whitledge not enough of bass and too much of treble. So i made up a curve that is somewhere in the middle between both, i.e. less bass than whitledge and less treble than half of whitledge.

    Screenshots for Subwoofer attached. First is for the wider gap, second with the more narrow gap (I verified that it's a Butterworth alignment if you use any of the Subwoofer or bass limited presets). Please note that i only used the overall curve for both to not have to load the single driver curves everytime.

    Click image for larger version. 

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    Either way. Both are not summing correctly as the more narrow gap should have a bump in the summed response and the LR24db alignment should sum flat, right?
    So i think i might have some phase issues in my system that should be solved regardless of the alignment i'm using.

    The one with the more shallow gap uses LR24db alignment as shown below for the midbass driver against the midbass curve from your spreadsheet.

    Click image for larger version. 

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    I think i put this in a seperate thread though as in my opinion it starts to get offtopic for this thread.
    Last edited by Cathul; 05-19-2020 at 12:33 AM.
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