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Author Topic: Choosing the best sub for me  (Read 41652 times)

Ivan Beaver

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Re: Choosing the best sub for me
« Reply #90 on: June 19, 2015, 09:42:36 PM »

I feel we are starting to come to a consensus.  On the point of phase shift due to crossover, if what Mac was saying is accurate, then I stand corrected.  I would like to understand how a crossover effects phase so much.  I think it ought to be a new thread though.  Which forum should it be in?
Just use any measurement system and look at the phase response

Run it through a high and low pass filter and observe
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Ivan Beaver
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Jacob Shaw

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Re: Choosing the best sub for me
« Reply #91 on: June 20, 2015, 03:57:03 PM »

Looking at the results of measurement does not seem to explain why the phase shift occurs, only that it occurs.  The concept that I am grappling with is how you can have negative latency.  Eli the ice man did help a little in explaining the phase relationship between current and voltage, although I will have to ponder on how this applies to latency in audio.
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Caleb Dueck

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Re: Choosing the best sub for me
« Reply #92 on: June 20, 2015, 04:01:14 PM »

You can't have negative latency, IE time travel.  Just added latency, IE delay, on the relatively early arrivals.

Look up how high and low pass filters work, electrically speaking.
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Mac Kerr

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Re: Choosing the best phase for me
« Reply #93 on: June 20, 2015, 09:03:05 PM »

Looking at the results of measurement does not seem to explain why the phase shift occurs, only that it occurs.  The concept that I am grappling with is how you can have negative latency.  Eli the ice man did help a little in explaining the phase relationship between current and voltage, although I will have to ponder on how this applies to latency in audio.

You don't have negative latency, you have PHASE SHIFT, the 2 are not the same thing. The only thing similar is that we use delay to partially fix phase alignment between 2 speakers that have a phase offset between them. Because we are not correcting the actual phase we can only fix it over a limited range, but that is usually enough to get us good summation through the crossover range. I use the term crossover range because it is in fact a range that is centered around the actual acoustic crossover frequency.

With modern digital processing we can fix the phase, but that would involve negative latency, which is not possible, so we shift everything later so everything is in the positive time domain. This is much of the reason correcting phase with FIR filters induces so much latency.

Mac
« Last Edit: June 20, 2015, 10:36:39 PM by Mac Kerr »
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Ivan Beaver

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Re: Choosing the best phase for me
« Reply #94 on: June 20, 2015, 10:12:16 PM »

Y I use the term crossover range because it is in fact a range that is centered around the actual acoustic crossover frequency.


Mac
And just to add-it is the ACOUSTIC crossover we are interested in, NOT the ELECTRICAL crossover.  Those are often very different-sometimes on the order of an octave.-but easily a half octave.
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Ivan Beaver
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Jacob Shaw

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Re: Choosing the best sub for me
« Reply #95 on: June 22, 2015, 11:20:00 AM »

According to what I read in a paper published by rane, a low pass causes a negative shift in phase near the crossover frequency, and a highpass causes a positive shift near the crossover frequency.  This suggests that a transducer receives the signal near the crossover frequency before it receives the higher frequencies.  How is this possible?  I understand how a capasitor can delay a signal because it stores energy, but how can a circuit advance a voltage signal?
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Ivan Beaver

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Re: Choosing the best sub for me
« Reply #96 on: June 22, 2015, 01:20:48 PM »

According to what I read in a paper published by rane, a low pass causes a negative shift in phase near the crossover frequency, and a highpass causes a positive shift near the crossover frequency.  This suggests that a transducer receives the signal near the crossover frequency before it receives the higher frequencies.  How is this possible?  I understand how a capasitor can delay a signal because it stores energy, but how can a circuit advance a voltage signal?
It is all "relative". One point relative to another.

 If you change your reference point, the phase will change.

Just look at the phase trace on any measurement program.  Now change the delay time and the phase will change.

It is simply the phase as relative to the delay time.
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A complex question is easily answered by a simple-easy to understand WRONG answer!

Ivan Beaver
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PHYSICS- NOT FADS!

Tim McCulloch

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Re: Choosing the best sub for me
« Reply #97 on: June 23, 2015, 09:36:32 AM »

I feel we are starting to come to a consensus.  On the point of phase shift due to crossover, if what Mac was saying is accurate, then I stand corrected.  I would like to understand how a crossover effects phase so much.  I think it ought to be a new thread though.  Which forum should it be in?

You need to read up on filters in general, and how they work.  The generic answer is "time."  The lower the center/corner frequency (as appropriate to the type of filter) and the steeper the slope (the number of poles to the filter), the longer it takes for the filter to do its job.

I was ready to give you the Flaming Twit Award (Mac is correct in his statements, and then some) but your interest in furthering your knowledge has postponed the ceremony.  It's reasonable to want to understand most fully the things that influence the DUT, but it's also acceptable to take to heart the statements of Mac, Ivan, Caleb and most of the others that have responded to your assertions.  They really DO know their shit and aren't just jerking your chain.

You would benefit from learning more about *measurement* as time (phase) is as the heart and soul of the process.  It's still up to the operator to make decisions about what is seen in Smaart/SysTune displays, but without these tools you're flying time-blind.

Does phase alignment make a difference?  Hell yes.  I did impulse alignments for a very long time and those represented an improvement over my prior techniques (flipping polarity of a pass band and delaying for max cancellation at crossover, then flipping back).  Jamie Anderson opened my ears and eyes in my first Smaart class in 2004.  I've never gone back to Thee Olde Wayz.  How much of a difference can phase alignment make?  Up to 6dB across almost 2 octaves.  Proper alignment can cut a significant amount of stuff from the truck pack.  The accountant likes that, the crew likes that, and the rigs sound better.
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Ivan Beaver

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Re: Choosing the best sub for me
« Reply #98 on: June 23, 2015, 12:42:43 PM »


Does phase alignment make a difference?  Hell yes.  I did impulse alignments for a very long time and those represented an improvement over my prior techniques (flipping polarity of a pass band and delaying for max cancellation at crossover, then flipping back).  Jamie Anderson opened my ears and eyes in my first Smaart class in 2004.  I've never gone back to Thee Olde Wayz.  How much of a difference can phase alignment make?  Up to 6dB across almost 2 octaves.  Proper alignment can cut a significant amount of stuff from the truck pack.  The accountant likes that, the crew likes that, and the rigs sound better.
The problem with delaying at one freq is that you can get a gain at THAT freq, but yet have dips on either side of crossover and not know it.

When you phase align (getting the drivers to act more like ONE driver), you get a better summation AND better sound quality.

I ALWAYS look an octave on either side of acoustic crossover to make sure I am not getting cancellations.

As with anything you have to look at the OVERALL issue-not just one little piece
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A complex question is easily answered by a simple-easy to understand WRONG answer!

Ivan Beaver
Danley Sound Labs

PHYSICS- NOT FADS!

Jacob Shaw

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Re: Choosing the best sub for me
« Reply #99 on: June 23, 2015, 12:47:09 PM »

I don't believe anyone is trying to mislead me, but I have read up on how crossover networks work, and I don't see that anyone has taken a stab at directly answering my question. 
  If you have a lonely 10" transducer on a highpass filter,  what causes it to reproduce the frequencies near the corner ahead of the higher frequencies? 
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Re: Choosing the best sub for me
« Reply #99 on: June 23, 2015, 12:47:09 PM »


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