Are single drivers really phase coherent?

chuck55 · 15th September 2008, 04:48 AM

Here is a question I've always wondered about.
Looking at the Jordan JX-92
JX-92

it shows the phase changing with frequency response. This is typical of all single driver speakers.
Does this mean the speaker would not be time and phase coherent?
If so, is ANY speaker truly time and phase coherent?

http://www.ejjordan.co.uk/drivers/jx92.html

norman bates · 15th September 2008, 06:17 AM

nope, they aren't.

but they have a large area where they are.

Norman

chuck55 · 15th September 2008, 02:49 PM

Wow!

So much for Theil, GMA, and all the rest.

phase_accurate · 16th September 2008, 10:18 AM

At their lower end and in the middle of their range fullrangers are usually excellent. Only a few are good at their upper end however.

But the Jordan driver in question is a particularly good one in this respect !

Regards

Charles

norman bates · 16th September 2008, 10:45 AM

I think a time aligned 2 or 3 way has a good chance at phase from low to highs.

I think gma claimed +/- 10 degrees from 100-20khz but I could be wrong.

Norman

phase_accurate · 16th September 2008, 11:55 AM

But then he might also have used a tweeter that is reaching > 100 kHz or used some electronic phase-compensation or he simply made a measurement error !

Regards

Charles

norman bates · 16th September 2008, 09:01 PM

true, I had not though of that.

It is tough on a 6db because rule of thumb is the driver need flat freq response 2 octaves beyond crossover point. Although some probably are flat only 1 octave.

And the driver will roll off when it hits its own rolloff point.

Thiel crossovers are quite large, I think they compensate for that but I'm unsure.

Norman

phase_accurate · 17th September 2008, 07:47 AM

Phase starts to deviate from zero long before the cutoff frequencies are reached. This can be seen very well in the diagrams of the aforementioned Jordan driver. So a speaker with an upper cutoff-frequency between 40 and 50 kHz will most probably show more than 10 degress of phase-lag at 20 kHz due to the rolloff alone. This could be corrected electronically however.

10 degrees of phase-shift at 20 kHz is the same as around 0.5mm of sound travel through the air. I wonder how someone determines the point in space - where a wave originates from - at this accuracy.

OTOH I don't doubt that the mentioned design as such is a competent one.

Regards

Charles

graaf · 19th September 2008, 11:58 AM

Quote:

Originally posted by chuck55
[B]If so, is ANY speaker truly time and phase coherent?

good single drivers are not perfect

BUT they are time and phase coherent ENOUGH to fool our hearing

multiways are not

best!
graaf

oshifis · 19th September 2008, 12:05 PM

Not flat phase response, but flat (and low) group delay is important.

15th September 2008, 04:48 AM	#1
chuck55 diyAudio Member Join Date: Dec 2003 Location: New England	Are single drivers really phase coherent? Here is a question I've always wondered about. Looking at the Jordan JX-92 JX-92 it shows the phase changing with frequency response. This is typical of all single driver speakers. Does this mean the speaker would not be time and phase coherent? If so, is ANY speaker truly time and phase coherent? http://www.ejjordan.co.uk/drivers/jx92.html

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15th September 2008, 06:17 AM	#2
norman bates diyAudio Member Join Date: Nov 2003 Location: iowa	nope, they aren't. but they have a large area where they are. Norman

15th September 2008, 02:49 PM	#3
chuck55 diyAudio Member Join Date: Dec 2003 Location: New England	Wow! So much for Theil, GMA, and all the rest.

16th September 2008, 10:18 AM	#4
phase_accurate diyAudio Member Join Date: May 2002 Location: Switzerland	At their lower end and in the middle of their range fullrangers are usually excellent. Only a few are good at their upper end however. But the Jordan driver in question is a particularly good one in this respect ! Regards Charles

16th September 2008, 10:45 AM	#5
norman bates diyAudio Member Join Date: Nov 2003 Location: iowa	I think a time aligned 2 or 3 way has a good chance at phase from low to highs. I think gma claimed +/- 10 degrees from 100-20khz but I could be wrong. Norman

16th September 2008, 11:55 AM	#6
phase_accurate diyAudio Member Join Date: May 2002 Location: Switzerland	But then he might also have used a tweeter that is reaching > 100 kHz or used some electronic phase-compensation or he simply made a measurement error ! Regards Charles

16th September 2008, 09:01 PM	#7
norman bates diyAudio Member Join Date: Nov 2003 Location: iowa	true, I had not though of that. It is tough on a 6db because rule of thumb is the driver need flat freq response 2 octaves beyond crossover point. Although some probably are flat only 1 octave. And the driver will roll off when it hits its own rolloff point. Thiel crossovers are quite large, I think they compensate for that but I'm unsure. Norman

17th September 2008, 07:47 AM	#8
phase_accurate diyAudio Member Join Date: May 2002 Location: Switzerland	Phase starts to deviate from zero long before the cutoff frequencies are reached. This can be seen very well in the diagrams of the aforementioned Jordan driver. So a speaker with an upper cutoff-frequency between 40 and 50 kHz will most probably show more than 10 degress of phase-lag at 20 kHz due to the rolloff alone. This could be corrected electronically however. 10 degrees of phase-shift at 20 kHz is the same as around 0.5mm of sound travel through the air. I wonder how someone determines the point in space - where a wave originates from - at this accuracy. OTOH I don't doubt that the mentioned design as such is a competent one. Regards Charles

19th September 2008, 12:05 PM	#10
oshifis diyAudio Member Join Date: Mar 2004 Location: Budapest, Hungary	Not flat phase response, but flat (and low) group delay is important.