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Old 5th December 2008, 04:36 AM   #1
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Default zobel / phase

dumb question, but how does a zobel affect phase response, if at all??
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Old 5th December 2008, 06:29 AM   #2
simon5 is offline simon5  Canada
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It will flatten the phase from an amplifier standpoint, but will not correct the phase from an audibility standpoint.

The amplifier will see something closer to a resistor, but it will not make the tweeter sounds better.

Often, I wonder why we are using Zobel in typical transistor designs... it only simplify slightly crossover designs at the expense of even more components.

I could be wrong, I'm not a professionnal, but that's how I see it.
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Old 5th December 2008, 01:15 PM   #3
sreten is offline sreten  United Kingdom
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Hi,

One of the reasons (rather than blindly) for using zobels or partial
zobels is to manipulate the phase response of the crossover.

The crossover for a zobelled bass/ mid driver will be very different
to a non-zobelled driver, phase and amplitude are affected.

Driven directly the zobel will not affect a drivers phase or response
for a typical transistor low source impedance voltage amplifier.

/sreten.
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Old 6th December 2008, 12:56 AM   #4
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re:'phase and amplitude are affected' -
I guess I need to refine my question, how predictable is the phase change of a zobel ?
i.e. can you say for an xover of given order, you will get a given amount of phase change, plus so much extra from the zobel (presumably above it's knee freq)?
( there will assumedly be some divergence between theory and reality, let's just consider it theoretically first...)
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Old 6th December 2008, 01:16 AM   #5
soongsc is offline soongsc  Taiwan
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Basically, if the impedance flattens out, so does the impedance phase. If one looks at some of the stereophile measurements, they show how impedance effects amplifier response. This is very real, but may be masked by how the driver itself performs.
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Old 6th December 2008, 02:22 AM   #6
Ron E is offline Ron E  United States
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It depends on how it is used.

The idea of a zobel separate from the crossover is a "cookbook" technique. Easy to explain, but only a small part of the story.... From professional designers you will see few "zobels" that merely cancel inductive rise - it is only another crossover component...to be manipulated like any other.
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Old 6th December 2008, 03:25 PM   #7
soongsc is offline soongsc  Taiwan
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Quite agree. When they are integrated with the XO design, it's possible to reduce total part count etc.
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Old 9th December 2008, 11:32 AM   #8
sreten is offline sreten  United Kingdom
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Quote:
Originally posted by PeteMcK
re:'phase and amplitude are affected' -
I guess I need to refine my question, how predictable is the phase change of a zobel ?
Hi,

The short answer is that it is not.

It depends and the load impedance and the source impedance.

A directly driven driver (low source impedance) it has little effect.
Via a crossover it does have an effect related to the crossover.

As stated often the crossover is fine without a full or partial zobel.

/sreten.
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Old 9th December 2008, 05:24 PM   #9
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Quote:
Originally posted by sreten
A directly driven driver (low source impedance) it has little effect.
Just in the latest aXp in the review of the Woofer Tester 3, examples are shown where it is very clear that both phase & impedance are flattened.

In this day when more & more people are using higher impedance amplifiers, this cannot be ignored.

dave
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Old 10th December 2008, 12:16 AM   #10
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Quote:
Originally posted by sreten


Hi,

The short answer is that it is not.

It depends and the load impedance and the source impedance.

A directly driven driver (low source impedance) it has little effect.
Via a crossover it does have an effect related to the crossover.

As stated often the crossover is fine without a full or partial zobel.

/sreten.

The impedance of the speaker varies widely with frequency.
It would be impossible to complete negate the impedance at every frequency.
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