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Old 3rd April 2008, 04:53 PM   #1
Anglo is offline Anglo  Canada
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Default Coherence

Boys!

This forum seems to be the right place for me to share my thoughts on coherence.

So, to the point of the matter. Is coherence a subjective audiophile artifact?

I think it is an audiophile artifact that musicians do not talk about or see here an inexistant problem in LIVE unamplified concerts. To me the absolute coherence is one of the Fullrange driver. To me, and this is where the discussion lies, a multi-way system is never coherent like a fullrange driver. I can add here that the Acoustats are also absolutely coherent but I`d like to stay with fullrange drivers to simplify the matter.

This all said, what I am saying is, while wanting and achieving full frequency response, coherence takes a beating because in order to achieve the full 20 to 20, one must use a different approach than just one single driver. This in turn is choosing one`s poison.

I am not saying that multi way system can't produce a cohesif message, but rather, I am saying that as coherent as a patched togther sound can be "cohesif" and one could say it is indeed coherent, one listening session on a Fullrange driver will show the listener how incoherent a multi-way truly is.

Is this subjective or can we say it is objective and in fact can be measured?
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Old 3rd April 2008, 09:04 PM   #2
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Hi Anglo,

Most Fullrange (really only widerange) drivers are 'coherent' over a limited range only, that range being size dependent, and typically good at voice frequencies.

I feel that the main difference is that the phase changes wrt frquency are not so sudden as when a crossover is used with multiple drivers - until - the FR driver hits a natural HF limit where its phase change can be so much worse than when compared to a small separate tweeter.
When this HF limit is reached the driver does not suddenly stop transducing, it does so out of phase and reproduction becomes dissonant as energies fail to arrive coherently. This being a reason for adding a supertweeter to take over if a FR does not (cannot) cope as accurately as we would wish.

Cheers .......... Graham.
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Old 3rd April 2008, 09:18 PM   #3
tinitus is offline tinitus  Europe
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I agree completely...phase issues from early rolloff is often neglected...but trying to achieve full bandwith has its own flaws...nothings perfect
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Old 3rd April 2008, 09:19 PM   #4
Anglo is offline Anglo  Canada
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hi Graham

Man, you guys are quite the bunch. I love your response!

O.K., I have to break this down a bit.

>Most Fullrange (really only widerange) drivers are 'coherent' over a limited range only, that range being size dependent, and typically good at voice frequencies.<

I agree, that the fullrange drivers are limited in frequency response. I eluded to that in my initial post; where I lose you is when you say coherent depending on the frequency range. To me, I never hear a tweeter playing the highs (as limited and somewhat compressed as they are)

>I feel that the main difference is that the phase changes wrt frquency are not so sudden as when a crossover is used with multiple drivers - until - the FR driver hits a natural HF limit where its phase change can be so much worse than when compared to a small separate tweeter. <

Yes sudden phase shifts are very obvious on coherence i.e B&W speakers.


>When this HF limit is reached the driver does not suddenly stop transducing, it does so out of phase and reproduction becomes dissonant as energies fail to arrive coherently. <

Go a little further here, if I may sk you to do so.

>This being a reason for adding a supertweeter to take over if a FR does not (cannot) cope as accurately as we would wish.<
...because of the phase shift only?
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Old 3rd April 2008, 09:22 PM   #5
Anglo is offline Anglo  Canada
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>Phase issues from ealry roll off<

This inturn creates directivity too, right?
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Old 3rd April 2008, 09:24 PM   #6
tinitus is offline tinitus  Europe
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Some experience improved bass with the use of supertweeters

btw...the most coherent speaker may very well be 4way, you just have figure out how to do he crossover
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Old 3rd April 2008, 09:48 PM   #7
tinitus is offline tinitus  Europe
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Quote:
Originally posted by Anglo
>Phase issues from ealry roll off<

This inturn creates directivity too, right?

I suppose so, and may be what experts would call a change in "polar response pattern"...which may be non cohesive
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Old 4th April 2008, 09:17 AM   #8
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Quote:
you just have figure out how to do he crossover
A time- and phase-coherent one of course !

Regards

Charles
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Old 4th April 2008, 11:13 AM   #9
Anglo is offline Anglo  Canada
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>A time- and phase-coherent one of course<

So, if coherence is all about time and phase then it can be measured...right?
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Old 4th April 2008, 03:02 PM   #10
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If the coherence that YOU are talking about is the same one that I am talking about: YES !!

Regards

Charles
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