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Why is ”bad phase tracking” really that bad?

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  • craigk
    replied
    Originally posted by a4eaudio View Post



    Craig - thanks for that link. Not only for the good technical info, but for the humor that Rod imparts in his writings. Laughed out loud reading about speakers on a Friday night.
    Glad you liked it.

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  • a4eaudio
    replied
    Originally posted by craigk View Post
    Regardless where you stand or sit, you will most likely be a different distance from each instrument. One could insinuate oneself into the very centre of the performers' space, but this is more likely to lead to your eviction from the venue than to improve your listening enjoyment.
    Craig - thanks for that link. Not only for the good technical info, but for the humor that Rod imparts in his writings. Laughed out loud reading about speakers on a Friday night.

    Leave a comment:


  • craigk
    replied
    http://sound.whsites.net/ptd.htm#s4

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  • jhollander
    replied
    Originally posted by Dave Bullet View Post

    I wonder therefore whether we focus too much on phase - knowing the measuring axis is never the listening axis in a real world situation, and therefore phase is different purely due to location.
    The measuring axis can be your listening axis. Certainly the design axis should be where you intend to listen. You should measure off axis to look for issues where you might have messed up the phase alignment.

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  • Dave Bullet
    replied
    I don't have a lot of build experience, and my theoretical knowledge is even less.... so take this with a grain of salt.

    Through all my reading, it seems the factors dominating the sound are:
    1. power response - avoiding slopes and baffle geometries that cause severe on axis or off axis peaks. Designing and measuring for just on-axis then finding you have a +3dB peak in the sensitive 2.5Khz - 4.5KHz area will make the speaker forward sounding and increase fatigue.

    2. Distortion. Asking a tweeter to play too low / shallow slope or a harder coned / domed woofer or mid playing too high (where primary breakup node non linear distortion lower down) will make a speaker harsh

    Phase seems to be mentioned after the above when it comes to designer trade offs and concerns. I'm not saying it should be ignored - but questioning its relative importance.

    I wonder therefore whether we focus too much on phase - knowing the measuring axis is never the listening axis in a real world situation, and therefore phase is different purely due to location.

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  • lasse
    replied
    Hi all,

    first I would like to thank you all for all the feedback on my initial questions in this thread. I have been offline for the better part of this day for pressing personal reasons and really need a good day to "digest" all the advice given by all of you.

    One thing stads out for me and that it really is a good idea to strive for good phase tracking in the overlap region and I will remodel my system to try to achieve that.

    I Will be back!!

    Thanks!!

    Best regards//lasse

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  • Dave Bullet
    replied
    Originally posted by ernperkins View Post

    Just to be clear, are you talking about a simulation or actual measured response?
    Measured response. By phase perfect I meant good tracking either side of of both Fc.

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  • ernperkins
    replied
    Originally posted by Dave Bullet View Post

    I had a "phase perfect" LR4 M/T @ 2KHz design. ruler flat on-axis (yes power response matters)..
    Just to be clear, are you talking about a simulation or actual measured response?

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  • Dave Bullet
    replied
    Originally posted by scottvalentin View Post

    That looks really good - I recall seeing your thread on HTGuide - you've put a lot of work into that crossover and it shows. Nice job!
    Cheers. It's been 11 years in the making. Largely because i put the hobby on hold. The tweeters' ferrofluid is probably drying up :-)

    I had a "phase perfect" LR4 M/T @ 2KHz design. ruler flat on-axis (yes power response matters). Anyway - it sounded worse than the tapered slope 3KHz steeper design I'm listening to now. Even though the mid and tweeter were padded to match sensitivity, the tweeter would dominate the mid on many recordings. Moving the Fc up fixed this, at the expense of increasing 3rd order HD on the mid. I might move it back down again. I'm also only playing on one speaker so have no idea of the imaging and soundstage presentation haha. I'm building the final cabinets as I'm pretty happy with the diffraction and driver placement.

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  • dlr
    replied
    To Lasse, understand that phase-tracking is not by default equal phase response of two drivers, it is achieving the intended phase response of the desired filtered responses. For instance, all odd-order Butterworth filters are intended to be 90 degrees out-of-phase or some multiple of that number (i.e. BW3 is 270 degrees) and are acceptable crossovers types for speaker systems with first order being the most used to my knowledge when it comes to Butterworth.

    Originally posted by Chris Roemer View Post
    From your 1st graph, I can see your Fc is near 2.5kHz (don't know if this is a sim, or actual measurement... whatever).
    Right at your Fc, it looks like the 2 drivers are "summing" +2-1/2dB (LR is typically +6, and BW is +3).
    I can also see that at Fc your drivers are OOP (out of phase) by about 100*. Theoretically, I'd reverse the tweeter to get them only 80* OOP. (They'd probably sum +3.5dB @ Fc then.)
    I think you mean that the filters are down, -6 or -3 db, at Fc. But that's not complete. LR sums flat on-axis with no off-axis lobing. Even-order Butterworth sums to +3db on-axis. Odd-order sums flat. All Butterworth filters have lobing off-axis as will pretty much all filters other than LR.

    dlr

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  • dlr
    replied
    I wrote a small program that allows you to examine and experiment with different acoustic crossover combinations (ideal drivers, of course). It's interesting to see the summed response of differing crossover types, slopes and offsets with sometimes surprising results.

    WinFilters

    dlr

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  • Mark65
    replied
    Originally posted by Dave Bullet View Post
    Below is my 3 way with phase data included. I had to use HBT extracted min phase as I could not use measured phase below my gated frequency to adequately design the W/M crossover. The curves are smoothed to 1/48th octave as that is what the HBT extraction process did. As you can see - woofer / mid line up nicely. This hit the LR2 target I was going for. I needed LR2 for healthy impedance in the midbass M/T isn't as good. I wanted steeper slopes for 2 reasons. 1. Midwoofer breakup node. 2. The seas tweeter did not like 2KHz (I don't care what people say - it wasn't forgiving on certain material and dominated the upper mid / lower treble with a harsh sound).
    I think the mid/tweet relationship is pretty darned good. Sure, the vertical "wrap" lines are not directly on top of each other, but the tracking above and below Fc is spot on. Lasse, my opinion on phase relationship is much the same as others here, in that having it track as closely as possible at least an octave above and below Fc is the goal. Will you reach that goal? And if not is it a problem? Only you can answer that, based on your preferences and your listening area. I also agree with Dave about letting the drivers tell you where they want to cross. I always start with a goal, and I sim xo's for the individual driver targets without looking at the overall summation, then adjust from there for phase and power response and largely ignore the individual targets and original Fc goal (while paying attention to potential driver issues, of course). So the end result is sometimes significantly different from the initial target. Now, if you want to see what difference your phase relationship makes, do some off axis measurements, and observe any differences at Fc. Then decide for yourself if they're objectionable or not, and whether is worth fussing over.

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  • scottvalentin
    replied
    Originally posted by Dave Bullet View Post
    Below is my 3 way with phase data included. I had to use HBT extracted min phase as I could not use measured phase below my gated frequency to adequately design the W/M crossover. The curves are smoothed to 1/48th octave as that is what the HBT extraction process did.

    As you can see - woofer / mid line up nicely. This hit the LR2 target I was going for. I needed LR2 for healthy impedance in the midbass

    M/T isn't as good. I wanted steeper slopes for 2 reasons. 1. Midwoofer breakup node. 2. The seas tweeter did not like 2KHz (I don't care what people say - it wasn't forgiving on certain material and dominated the upper mid / lower treble with a harsh sound).
    That looks really good - I recall seeing your thread on HTGuide - you've put a lot of work into that crossover and it shows. Nice job!

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  • jhollander
    replied
    I would add the baffle to the tweeter and woofer to improve your prediction.

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  • lasse
    replied
    Hi,

    I just realized one (embarrassing, perhaps one of many…) mistake in my modelling.

    I have not extrapolated the tweeter response 2nd order at low fq´s before extracting phase……

    Will be back with better phase information.

    Regards//lasse

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