Page 2 of 2 FirstFirst 12
Results 11 to 17 of 17

Thread: O-scope, crossovers, and delay

  1. Back To Top    #11

    Re: O-scope, crossovers, and delay

    Quote Originally Posted by Justin Zazzi View Post
    I think the middle cycle where the two speakers overlap will be twice as tall because they should sum together.
    At least, this is how it might look in a textbook before real-life makes it messy.

    OMG you HAVE to try this!


    Attachment 10584

    I'll try some of this in the next couple of days, but I think for an 80 hz xover example (one cycle is 12.5 ms) the added delay would just delay every frequency by 12.5 ms, making things much worse. Enter the all-pass filter, for the win, maybe, if real life doesn't screw it up.

  2. Back To Top    #12

    Re: O-scope, crossovers, and delay

    I almost forgot the screenshots of the different delay from the phase adjustment on the amplifier. First is the 0 degree setting, second is the 180 degree setting, horizontal scale is 50 ms per major division with hash marks at 10 ms, vertical scale is 100 mV per major division with hash marks at 10 mV. Excuse me, 20 mV hashes.
    Attachment 10626
    Attachment 10627
    Last edited by ckirocz28; 05-02-2020 at 10:31 PM.

  3. Back To Top    #13

    Re: O-scope, crossovers, and delay

    Invalid links

  4. Back To Top    #14
    Wave Shepherd - aka Jazzi Justin Zazzi's Avatar
    Location
    Northridge, CA
    Posts
    670
    Join Date
    Aug 2018

    Re: O-scope, crossovers, and delay

    Quote Originally Posted by ckirocz28 View Post
    Ok, after some modeling, I've learned that the xovers only add group delay (same group delay for LP and HP) and the processing time is under 1ms in most cases, so totally ignore the above mentioned math.
    After some more experimenting, I've discovered the cause, my subwoofer amps have a phase adjustment control that seems to be a straight delay circuit, set at 180 degrees there is 10ms less delay than having it set at 0 degrees. So I am totally blaming the subwoofer amps for the additional delay. Maybe someone else with an amp with a phase control can test their amp and see if this is the case for all of this type phase control.

    I hope this little investigation will help someone else.
    If it is truly a phase adjustment knob, then it will be a variable time delay that is frequency dependent. A 10ms delay at 80 doesn't mean you'll get a 10ms delay at 70hz too.

    If it is a polarity switch and mislabeled as a phase knob (which is totally possible), then it will just make the ups and downs on the scope go flippy-floppy.
    Measure with mics, mark with chalk, cut with torch, grind to fit, sand to finish, paint to match.
    Updated Justin tuning sheet (Justin and Erica tuning companion for SMAART and REW)
    Do it for them.

  5. Back To Top    #15

    Re: O-scope, crossovers, and delay

    Quote Originally Posted by Justin Zazzi View Post
    I think the middle cycle where the two speakers overlap will be twice as tall because they should sum together.
    At least, this is how it might look in a textbook before real-life makes it messy.

    OMG you HAVE to try this!


    Attachment 10584
    I wish I was set up to try this - I have ZERO equipment with a delay set up right now. I have an O-scope, so technically I could perfectly align them...

    If someone can do this, here's my prediction:
    You wouldn't notice. Especially at higher frequencies. At least not with a single frequency.
    The problem with this also is that it's ONLY going to align at a single frequency. So in actuality, with full-range music - you'd definitely notice.

    The reason is - if you aligned it at, say, 100hz - then at 100hz, you probably wouldn't notice. The waves are perfectly aligned -zero loss, really. You'd never notice "one wave's worth" on one side or the other.
    But what you've really done is create a delay with a time factor equal to one wave (whatever time that calculates out to at 100hz, using the speed of sound and 100 cycles per second).
    So - progressively - as you move away from 100hz in the lower direction, your waves will fall out of alignment and gradually cancel increasingly...if I'm thinking about this right (one octave = half or double the frequency), 50hz would cancel. Maybe I'm thinking of time wrong, or not thinking of it all in my head - but there will be some point where it shifts enough to cancel entirely.

    And - as you move away from 100hz in the upper direction, your waves will fall out of alignment and gradually cancel increasingly also...
    BUT - we have many more octaves in this direction. So I think by the time you reach 200 cycles per second (unless, again, my mental math is not factoring in time), you'll completely cancel - but then by 400hz you'll be back in alignment. 800 hz, more cancellation... 1600 hz back in alignment. Etc.

    So you create that "comb pattern" that is bad news:
    https://audiouniversityonline.com/co...ing-explained/
    The leading image there shows an actually aligned response on top, and a slightly offset response on the bottom (as measured from a listening position).

    Not to complicate things further - but we inherently suffer this in car audio. Just from sitting off-center, in a car - you get this delay, inherently. And while you can fix it for one side OR the other by introducing delay, you can't fix it for both sides - if you add delay to the left speaker to fix it for the driver's side, you inherently compound the problem for the passenger's side. It's why people try to put their stereo speakers at the furthest distance possible for any given interior, as that equalizes the two pathlength distances - therefore minimizing this delay effect.

  6. Back To Top    #16

    Re: O-scope, crossovers, and delay

    Quote Originally Posted by Justin Zazzi View Post
    If it is truly a phase adjustment knob, then it will be a variable time delay that is frequency dependent. A 10ms delay at 80 doesn't mean you'll get a 10ms delay at 70hz too.

    If it is a polarity switch and mislabeled as a phase knob (which is totally possible), then it will just make the ups and downs on the scope go flippy-floppy.
    I watched the o-scope as I turned the phase adjustment, it literally just added 10 ms delay at 0 degrees and none at 180 degrees (other than the base 14 ms delay), with no change between the two.

  7. Back To Top    #17

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Back To Top