Are single drivers really phase coherent? - diyAudio
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Old 15th September 2008, 04:48 AM   #1
chuck55 is offline chuck55  United States
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Default 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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Old 15th September 2008, 06:17 AM   #2
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nope, they aren't.

but they have a large area where they are.

Norman
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Old 15th September 2008, 02:49 PM   #3
chuck55 is offline chuck55  United States
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Wow!

So much for Theil, GMA, and all the rest.
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Old 16th September 2008, 10:18 AM   #4
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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
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Old 16th September 2008, 10:45 AM   #5
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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
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Old 16th September 2008, 11:55 AM   #6
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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 !

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Charles
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Old 16th September 2008, 09:01 PM   #7
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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
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Old 17th September 2008, 07:47 AM   #8
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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
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Old 19th September 2008, 11:58 AM   #9
graaf is offline graaf  Poland
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Default Re: Are single drivers really phase coherent?

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
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Old 19th September 2008, 12:05 PM   #10
oshifis is offline oshifis  Hungary
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Not flat phase response, but flat (and low) group delay is important.
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