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Author Topic: Tweaking DR260 Factory Setting for SRX722  (Read 479 times)

Mike Karseboom

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Tweaking DR260 Factory Setting for SRX722
« on: May 01, 2014, 09:56:05 am »

I have a question about the advisability of making a change to a DR260 factory setting. 


The "program" is for an SRX722  run passive over an SRX728.  The speakers are driven  from  identical Xti4000 amps run stereo with attenuators fully open.  The program can be keyed in manually from the JBL published tunings.  The same settings can be achieved by using the Wizard on the DR260.


Systune is used to provide a pink noise signal and a dual FFT measurement is made with the DR260 as the Device under test.  Prior to testing, a hard wire is used to bypass the DR260 to verify that the measurement setup yields a perfectly flat frequency and phase response.  It does so the assumption is that during testing any frequency and phase response changes are due only to the DR260.


The question relates to the phase response and whether a delay should be added to the sub channel output.  Note that the measurements here are purely the electrical output of the DR260, not acoustic measurements.  I am just looking at a "baseline" response from the DR260 and so will also assume that the speakers would be set up with the 722's directly over the 728's with the front grills aligned.  That is- the physical spacing of the speakers is not a factor  of itself that would affect phase alignment.


The screen shot below shows:
Mid-High output    RED
Subs - No Delay    Dark Grey
Subs - 3ms Delay  Light Blue


The factory settings show the sub and mid-high outputs tracking along with each other very nicely for an extended range of frequencies on both sides of the crossover  point (about 78Hz).  But there is also a consistent 75 degrees of phase shift throughout the crossover area.   It seems to me that right around the crossover area a better alignment is achieved by adding the 3ms of delay to the sub bandpass.  Yet I am reluctant to second guess the Harmon engineers and there vastly superior experience.


Would you add the 3ms delay and expect to have better phase alignment at the crossover (at least electrically)?
Or is there some other factor I am not considering that make the factory tuning superior?











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--Mike
"If your not confused, you don't know what is going on"

Live Sound for the Mt. Shasta area
http://www.shastalivesound.com

David Sturzenbecher

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Re: Tweaking DR260 Factory Setting for SRX722
« Reply #1 on: May 01, 2014, 10:04:56 am »

I have a question about the advisability of making a change to a DR260 factory setting. 


The "program" is for an SRX722  run passive over an SRX728.  The speakers are driven  from  identical Xti4000 amps run stereo with attenuators fully open.  The program can be keyed in manually from the JBL published tunings.  The same settings can be achieved by using the Wizard on the DR260.


Systune is used to provide a pink noise signal and a dual FFT measurement is made with the DR260 as the Device under test.  Prior to testing, a hard wire is used to bypass the DR260 to verify that the measurement setup yields a perfectly flat frequency and phase response.  It does so the assumption is that during testing any frequency and phase response changes are due only to the DR260.


The question relates to the phase response and whether a delay should be added to the sub channel output.  Note that the measurements here are purely the electrical output of the DR260, not acoustic measurements.  I am just looking at a "baseline" response from the DR260 and so will also assume that the speakers would be set up with the 722's directly over the 728's with the front grills aligned.  That is- the physical spacing of the speakers is not a factor  of itself that would affect phase alignment.


The screen shot below shows:
Mid-High output    RED
Subs - No Delay    Dark Grey
Subs - 3ms Delay  Light Blue


The factory settings show the sub and mid-high outputs tracking along with each other very nicely for an extended range of frequencies on both sides of the crossover  point (about 78Hz).  But there is also a consistent 75 degrees of phase shift throughout the crossover area.   It seems to me that right around the crossover area a better alignment is achieved by adding the 3ms of delay to the sub bandpass.  Yet I am reluctant to second guess the Harmon engineers and there vastly superior experience.


Would you add the 3ms delay and expect to have better phase alignment at the crossover (at least electrically)?
Or is there some other factor I am not considering that make the factory tuning superior?

It is the acoustical response that matters, not just the electrical. Based on what you have posted, you have systune, which is a good start.  Do you have a mic?  Even if you just have an SM58, you should be able to see the relative phase response between the 722 and 728.
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Mike Karseboom

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Re: Tweaking DR260 Factory Setting for SRX722
« Reply #2 on: May 01, 2014, 11:04:11 am »

David- thank you for your reply.  I do realize it is the acoustic response that matters and would always ultimately defer to the results of the acoustic testing results.  I have the DBX RTA mic and have used Systune to take acoustic measurements a couple dozen or more times.  Unfortunately that process has usually resulted in traces fraught with anomalies and the results have been hard to replicate or interpret.    It it mostly my skill level but also I don't have a good space (open field) in which to make measurements. 


Notwithstanding the final acoustic results, wouldn't you think the DR260 electrical output should produce a phase response at the crossover that is a little tighter than 70-80 degrees out of phase?  I mean as a "baseline" correct response that then gets further tweeking  with acoustic measurments.


Or is there some sort of "group delay" with the SRX728 physical box that would result in an effective 3ms delay that is being taken into account by the DR260 factory setting?
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--Mike
"If your not confused, you don't know what is going on"

Live Sound for the Mt. Shasta area
http://www.shastalivesound.com

Doug Fowler

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Re: Tweaking DR260 Factory Setting for SRX722
« Reply #3 on: May 01, 2014, 11:55:06 am »

 


Notwithstanding the final acoustic results, wouldn't you think the DR260 electrical output should produce a phase response at the crossover that is a little tighter than 70-80 degrees out of phase?  I mean as a "baseline" correct response that then gets further tweeking  with acoustic measurments.


Not if that's what it takes to get the acoustic response right.
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Mike Karseboom

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Re: Tweaking DR260 Factory Setting for SRX722
« Reply #4 on: May 01, 2014, 07:22:10 pm »

Not if that's what it takes to get the acoustic response right.


I did an acoustic measurement with the SRX722 on top of an SRX728 focusing on the phase at the crossover.  It does indeed seem like there is a good alignment with no delay added.  Adding delay makes it worse.


Nice to see it working well this way and in the future I won't put too much emphasis on the electrical response and focus more on the acoustic measurements.












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--Mike
"If your not confused, you don't know what is going on"

Live Sound for the Mt. Shasta area
http://www.shastalivesound.com
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