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Author Topic: Delay mains vs subs  (Read 6581 times)

Luke Geis

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Re: Delay mains vs subs
« Reply #30 on: October 24, 2018, 04:24:23 PM »

Tim,

   Worded sorta wrong, but clarified at the same time. The phase shift is advanced by half the group delay for hi's and the lows of course lag by the other half of the total group delay. When we measure we see the leading phase as essentially zero and the total phase shift between the two halves is, of course, the total of the group delay.

It is otherwise known as phase lead and phase lag. The use of time to describe the phase lead was a little off course, but the idea was to give the notion that there is an advance and a retard that occurs within the filter network. If we look at it from a time perspective the impulse that we see from the hi's would be ahead in time of the lows. The amount of time ahead would be the total of the group delay.

This link touches on it and was one of the first I could find about phase lead and phase lag:

https://www.electronics-tutorials.ws/filter/filter_3.html
« Last Edit: October 24, 2018, 04:33:16 PM by Luke Geis »
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Tim McCulloch

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Re: Delay mains vs subs
« Reply #31 on: October 24, 2018, 04:52:57 PM »

Tim,

   Worded sorta wrong, but clarified at the same time. The phase shift is advanced by half the group delay for hi's and the lows of course lag by the other half of the total group delay. When we measure we see the leading phase as essentially zero and the total phase shift between the two halves is, of course, the total of the group delay.

It is otherwise known as phase lead and phase lag. The use of time to describe the phase lead was a little off course, but the idea was to give the notion that there is an advance and a retard that occurs within the filter network. If we look at it from a time perspective the impulse that we see from the hi's would be ahead in time of the lows. The amount of time ahead would be the total of the group delay.

Maybe it's a semantics thing but it is not possible for a filter to "advance" time.  That's my point.  Whatever the *measurement* moment of origin (the zero point), everything happens after it or you moved the starting line.
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Luke Geis

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Re: Delay mains vs subs
« Reply #32 on: October 24, 2018, 09:27:49 PM »

I think the phase lead has more to do with the charging of the capacitors because of the AC nature of an audio signal. Basically, it comes down to math that for this thread is over the top. While I won't say it physically advances in time, the phase shift in the positive direction ( which indicates a phase shift that is ahead in time ) does preclude the signal. Looking at the webpage I directed, it prescribes that the input starts at +45* ahead of the input and then of course shifts to the nominal phase shortly thereafter. The lower portion of the passband does not shift back to zero however. In either case, it is a phenomenon and a consideration.

When we use Smaart and other such tools to align the phase slopes, the phase shift of the subs relative to the mains is a measurement of the acoustic average and not so much the electrical anomalies that math prescribes. The averaging, weighting and sample frequency of the measurement is surely much lower in resolution than the electrical actuality, not that we could " see it " in the air anyway. In short, we simply couldn't see or hear that phase lead anyway. We align the impulse/phase slopes to the best we can and it is close enough at the areas that count to work.

Many years have gone by where subs and mains were grossly misaligned and the people have been happy enough if not enthralled by the quality of the sound. Be it by total accident or simply that we can't really tell in a blind situation the basic way that nearly 100% of new " sound guys " have been doing it since the beginning of time has worked well enough for most. The cream rises to the top and those with a greater understanding tend to get better and more consistent results with less work and effort required. Knowing is half the battle while implementing and applying that knowledge is the other half.
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Re: Delay mains vs subs
« Reply #32 on: October 24, 2018, 09:27:49 PM »


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