zobel / phase

PeteMcK · 5th December 2008, 04:36 AM

dumb question, but how does a zobel affect phase response, if at all??

simon5 · 5th December 2008, 06:29 AM

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.

sreten · 5th December 2008, 01:15 PM

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.

PeteMcK · 6th December 2008, 12:56 AM

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...)

soongsc · 6th December 2008, 01:16 AM

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.

Ron E · 6th December 2008, 02:22 AM

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.

soongsc · 6th December 2008, 03:25 PM

Quite agree. When they are integrated with the XO design, it's possible to reduce total part count etc.

sreten · 9th December 2008, 11:32 AM

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.

planet10 · 9th December 2008, 05:24 PM

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

nigelwright7557 · 10th December 2008, 12:16 AM

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.

5th December 2008, 04:36 AM	#1
PeteMcK diyAudio Member Join Date: Feb 2002 Location: Western Sydney	zobel / phase dumb question, but how does a zobel affect phase response, if at all?? __________________ Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency

5th December 2008, 06:29 AM	#2
simon5 diyAudio Member Join Date: Nov 2004 Location: Québec, Québec	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. __________________ DIYaudio for President !

6th December 2008, 12:56 AM	#4
PeteMcK diyAudio Member Join Date: Feb 2002 Location: Western Sydney	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...) __________________ Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency

6th December 2008, 01:16 AM	#5
soongsc diyAudio Member Join Date: Mar 2005 Location: Taiwan	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. __________________ Hear the real thing!

6th December 2008, 02:22 AM	#6
Ron E diyAudio Member Join Date: Jun 2002 Location: USA, MN	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. __________________ Our species needs, and deserves, a citizenry with minds wide awake and a basic understanding of how the world works. --Carl Sagan Armaments, universal debt, and planned obsolescence--those are the three pillars of Western prosperity. —Aldous Huxley


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5th December 2008, 01:15 PM	#3
sreten diyAudio Member Join Date: Nov 2003 Location: Brighton UK	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.

6th December 2008, 03:25 PM	#7
soongsc diyAudio Member Join Date: Mar 2005 Location: Taiwan	Quite agree. When they are integrated with the XO design, it's possible to reduce total part count etc. __________________ Hear the real thing!

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