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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => Audio Measurement and Testing => Topic started by: Mike Karseboom on April 27, 2015, 12:37:51 am

Title: New Amp / New Delay?
Post by: Mike Karseboom on April 27, 2015, 12:37:51 am
Well not new, but different.  I made some FFT measurements in a venue to get a good phase alignment  around the crossover frequency between the passive subs and powered tops at representative point on the dance floor.  I ended up with a 20ms delay on the subs and a pretty good alignment with the phase curves using systune.


When I took the measurements the passive subs were being powered by a indestructible old Peavey CS1200.  But now I want to drive these same subs with a PLX3402.  The tops and physical aspects all remain the same.


Do I need to make new measurements to check the delay or can I assume the PLX3402 will not change the phase response of the subs.   (apologies if I have not phrased this correctly).
Title: Re: New Amp / New Delay?
Post by: Mac Kerr on April 27, 2015, 12:58:44 am
When I took the measurements the passive subs were being powered by a indestructible old Peavey CS1200.  But now I want to drive these same subs with a PLX3402.  The tops and physical aspects all remain the same.


Do I need to make new measurements to check the delay or can I assume the PLX3402 will not change the phase response of the subs.   (apologies if I have not phrased this correctly).

The new amp will not make a change.

Mac
Title: Re: New Amp / New Delay?
Post by: Mike Karseboom on April 27, 2015, 01:25:58 am
The new amp will not make a change.

Mac


That is what I was hoping /assuming.  I guess my thought was that unless the amp has DSP, like an XTI-4000, that I would not have to make any changes.  So all my various PLX, PLX2,  and old iron crowns can all be considered "analog" with "instantaneous" electrical response.


On a slightly different tack - if I keep everything the same but change one set of passive subs for another model, should I assume that the new subs will need a new measurement  to check for phase?  Probably not the right terminology again - but should I assume that a different box will likely have a different group delay and require a new alignment measurement.
Title: Re: New Amp / New Delay?
Post by: Ivan Beaver on April 27, 2015, 07:32:26 am

That is what I was hoping /assuming.  I guess my thought was that unless the amp has DSP, like an XTI-4000, that I would not have to make any changes.  So all my various PLX, PLX2,  and old iron crowns can all be considered "analog" with "instantaneous" electrical response.


On a slightly different tack - if I keep everything the same but change one set of passive subs for another model, should I assume that the new subs will need a new measurement  to check for phase?  Probably not the right terminology again - but should I assume that a different box will likely have a different group delay and require a new alignment measurement.
If your subs are in a physical different place than the mains (say subs on floor and mains flown) , then I would not worry about any little differences that some amps might have-even an amp with processing).

Because as soon as you move your mic a little bit-your delay time will need to be changed.

Not enough to worry about.

The same thing goes for changing out sub boxes (unless you are going to or from a reflex box to a horn box).  With spaced devices, you can only get the delay "correct" in one position.  Move that position and the delay changes.

So you simply choose some position that "makes sense" and get it right there, knowing everywhere else will be "incorrect".

It is real easy to get "hung up" on the little things that overall don't make a difference.

You always have to ask yourself "What am I here to do?".