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Phase filter on XTA DP448 uses?
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PolymorphicMark View Drop Down
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    Posted: 18 February 2012 at 1:56am
I do not own a xta dp448 but was looking through the manual for one. I noticed it has a filter type called a Phase Filter. I'm trying to work out what you would use this type of filter for? I was wondering if you could use it adjust the phase shift on say a bass reflex cab so it effectively has zero phase shift. I'm sure I''ve miss understood this type of filter and it uses so any help understanding it would be much appreciated.

Thanks, Mark
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Tedski View Drop Down
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Points: 333 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Tedski Quote  Post ReplyReply Direct Link To This Post Posted: 18 February 2012 at 6:12am
I understand what it does, but I'm a bit hazy on why you would need it as well, although I can grasp it's potential.

http://en.wikipedia.org/wiki/All-pass_filter





Edited by Tedski - 18 February 2012 at 6:20am
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Smiter View Drop Down
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It'll adjust the phase referenced to a certain frequency. Can be useful if tuning a system with tight crossover points.
 
 
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PolymorphicMark View Drop Down
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Points: 239 		Post Options Post Options   Thanks (0) Thanks(0)   Quote PolymorphicMark Quote  Post ReplyReply Direct Link To This Post Posted: 18 February 2012 at 2:22pm
Smiter can you expand on this please.
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PolymorphicMark View Drop Down
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Points: 239 		Post Options Post Options   Thanks (0) Thanks(0)   Quote PolymorphicMark Quote  Post ReplyReply Direct Link To This Post Posted: 18 February 2012 at 2:25pm
Originally posted by Tedski Tedski wrote:




I understand what it does, but I'm a bit hazy on why you would need it as well, although I can grasp it's potential.

http://en.wikipedia.org/wiki/All-pass_filter



The link you have given talks about All-phase filters which according to XTA are different. The DP448 has All-Pass filters and Phase filters?






Edited by PolymorphicMark - 18 February 2012 at 2:26pm
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The Phase filter is a different filter compared to the all-pass filter .
The phase filter adjusts phase over the intire freqency range on the output channel selected . Where the all-pass filter (2nd order within the XTA) will only give you phase shift @ a selected frequency range (select with bandwith) .
 
As phase is time over frequency you can use the all-pass filter to phase align drivers without the use of delay and to correct the phase response of the complete system .
To do so you have to have a measurement device so FFT analyzer and a good knowledge of how phase works . Also it will take some time to figure out how to make it work the way you want it to work .
 
go to the "Back to the future" post or start with the "How to change the phase response of a loudspeaker"post on my blog . This is where i use the 2nd order all-pass filters .
I did play around with a phase filter within my BSS BLU80's units but i do not have any data on these stored up to now .
I did try them a few times and @ that time i could adjust the phase trace in the real high end witch was going up (during that measurement) and move it down again to the 0dg line . 
The sound will be as good as the band play's
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PolymorphicMark View Drop Down
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Points: 239 		Post Options Post Options   Thanks (0) Thanks(0)   Quote PolymorphicMark Quote  Post ReplyReply Direct Link To This Post Posted: 22 February 2012 at 1:26pm
Thanks for the response Timo, nice of you to take the time for the in depth reply. I will check out the literature on your website.
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You can't just pick a frequency on the 448 and change its phase without altering the whole band. If you could, it would be amazing!
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Points: 62 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Timo Beckman Quote  Post ReplyReply Direct Link To This Post Posted: 22 February 2012 at 5:39pm
You can change the time on a small part of the response of the system by using 2nd order allpass filters if the have the abillity to change the bandwith of the filter .
 
Again you need a firm understanding of phase and where to apply the filter, a FFT analyzer and know where to put the microphone .
 
With multiple loudspeakers you can use the allpass to do a real phase allignment as to just time aligning als loudspeakers within that system . It means for instance That a 2way system witch will probably have less "time smear" can be phase corrected to match a 3 or more way system .
The sound will be as good as the band play's
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