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Author Topic: Group Delay  (Read 17034 times)

Doug Fowler

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Re: Group Delay
« Reply #20 on: November 25, 2012, 02:25:23 pm »

Since the topic of group delay is being discussed,can anyone describe the procedure to delay cabinets or subs using the group delay function? Is it as simple as delaying until the delay in ms is the same or close at the crossover frequency?

Thanks.

Yes it is possible, but group delay is very sensitive to noise.  With very good measurements it is a simple matter to adjust delay so that the frequencies of interest are aligned to the extent possible. 

I did demonstrations of this very procedure a couple of years ago at InfoComm using SysTune.   



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Phil Graham

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Re: Group Delay
« Reply #21 on: November 26, 2012, 09:35:28 am »

Since the topic of group delay is being discussed,can anyone describe the procedure to delay cabinets or subs using the group delay function? Is it as simple as delaying until the delay in ms is the same or close at the crossover frequency?

Thanks.

Alfredo,

A derivative tracks the rate of change of a signal. With noise on the signal, the derivative can oscillate wildly. If you have a "smooth," low noise phase trace, then doing the alignment with group delay is as simple as you imagine. The trick is getting a phase trace smooth enough that you can generate a well behaved derivative thereof.
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Phil Graham

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Re: Group Delay
« Reply #22 on: November 26, 2012, 09:40:46 am »

What direction does the nonlinear artifacts push things? Vs more group delay or less? Also how do you distinguish between where it goes from linear to nonlinear, its a gradual process right?

It doesn't really push them. The nonlinear artifacts generate new frequency components from the transducer, and to a first order approximation the relative phase of each of those components follows the global, linear phase response output of the speaker. The big issue is not shifting of the relative arrival, but rather production of new frequency components.
 
Quote
Applies for MF/HF too or?

The pulse spreading phenomenon is universally applicable for minimum phase (or greater) bandpass filters, independent of the frequencies involved. It is most obvious at low frequencies, as this is where the group delay is the largest.
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Rasmus Rosenberg

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Re: Group Delay
« Reply #23 on: December 14, 2012, 02:26:18 pm »

Thanks Phil,
It is not possible to change the Group delay of a speaker with out changing the Phase response, or ?

mvh
R
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Phil Graham

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Re: Group Delay
« Reply #24 on: December 19, 2012, 10:22:28 am »

Thanks Phil,
It is not possible to change the Group delay of a speaker with out changing the Phase response, or ?

mvh
R

You can change the total group delay by moving father away :) as the slope of the phase response due to pure acoustic delay is a straight line, and therefore the derivative is therefore a constant.

Otherwise, since the group delay is defined mathematically from the phase, they are linked at the hip.
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Rasmus Rosenberg

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Re: Group Delay
« Reply #25 on: December 20, 2012, 04:24:45 am »

You can change the total group delay by moving father away :) as the slope of the phase response due to pure acoustic delay is a straight line, and therefore the derivative is therefore a constant.

Otherwise, since the group delay is defined mathematically from the phase, they are linked at the hip.

Thanks Phil,
Really appreciate you commenting, Its such a pleasure to be able to get a clear, complicated, but correct answer to all the "grey zones" i audio knowledge, especially for one with a non mathematical background.
Its actually really fun because i have just been "grilled" in the field this past season by two parties, a competing software manufacture and a speaker manufacture, about group delay and its "difference and comparison" from the phase trace, and after showing them this post, it turns out I was right from the start, and got an apology.. 
/R
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Irwan Prasetyo

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Re: Group Delay
« Reply #26 on: May 05, 2014, 06:54:25 am »

Try this one instead, http://www.excelsior-audio.com/Publications/Phase_Response_&_Receive_Delay.pdf.

After that you might find this one interesting http://www.excelsior-audio.com/Publications/Subwoofer_Alignment.pdf.

Hello, this post is around one year ago.But i hope it's not too late to "up" this topic.
After read Charlie article, i try many times to consider group delay when alignment beetwen fullrange & sub.
I attach some pict from one of my measurement.The distance beetwen mic to spkr is around 20m.
Pict 1 is response of fullrange & sub has aligned.And we can see the summation.
But after look inside into group delay curve, this system have high group delay (pict 2).

Pict 3 is response of system after fine tune, so the group delay getting lower than before.

Pict 4 is response of system which have low group delay & we can see the phase response is not align anymore.But the freq response is still show good summation.

Pict 5 is compare group delay beetwen before & after fine tune.
Pink curve = before & Blue curve = after

My question is :
1.Why the summation is not change after the phase response not align anymore?
2.which one that you choose beetwen this two comparative response??because frequency response doesn't change, only the phase & group delay is different.
Thanks & any advice will be appreciate.
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Re: Group Delay
« Reply #26 on: May 05, 2014, 06:54:25 am »


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