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Old 16th March 2004, 02:35 AM   #1
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Default Zobel Network

Ok I did do a search but couldn't find my answer. From what I have read on other sites dedicated to crossover design, a Zobel network is used to "stabalize a speaker's impediance". What I mean is it is supposed to get rid/help against peaks in impedance. Now my question is how much of a differance would one of these make when used on a subwoofer in the car audio relm? the way I see it if the impedance rises from the nominal 4 ohms to say 7 ohms, the amps power is almost cut in half at that frequency. Will a zobel network help stabalize the subs impedance at 4ohms? Or is it just a waste of time?

Thanks,

D.
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Old 16th March 2004, 04:31 AM   #2
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A Zobel cancels the rise in impedance of a speaker due to the inductance of the voice coil and makes it easier to design passive crossovers. Networks which compensate for an impedance peak such as seen at resonance are not called Zobels. In a car situation with electronic crossovers a Zobel is not needed.

On the other hand, zobels are just a resistor and cap and as such are cheap. I've never heard of an instance where they hurt anything and some say the sound is better with one, regardless.
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Old 16th March 2004, 05:43 AM   #3
Vivek is offline Vivek  India
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nuttinbutSQ, see http://lalena.com/audio/
I am designing a two way speaker. So, I would use a crossover filter and an impedance equalisation circuit for both the woofer and tweeter. I hope I am right.
Vivek
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Old 16th March 2004, 07:08 AM   #4
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For a passive 2-way system, it will be useful to have a C-R network across the bass unit to compensate for the rising impedance at higher frequencies due to the voice coil inductance. (Otherwise the attenuation of the HF signal out of the crossover won't be as much as you expect it to be).

It may also be useful to have a L-C-R network across the tweeter to compensate for the rise in inductance at resonance.

However, if your tweeter is more efficient than the bass unit, and has a resistive pad to drop the signal level, then you may find that the rise in impedance at resonance (as seen by the output of the HF section of the crossover network) isn't enough to need the L-C-R network. This is because the resistor across the tweeter reduces the rise in impedance at resonance.
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Old 16th March 2004, 07:25 AM   #5
sunil is offline sunil  India
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Hi,

Please read http://sound.westhost.com/lr-passive.htm.
It is well written, lucid, no b-s & easy to understand. It explains the whole thing, the why, how & what of passive X/O's
& yes, it answers your questions about zobels' as well.

cheers,
sunil
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Old 16th March 2004, 07:50 AM   #6
sreten is offline sreten  United Kingdom
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JMO but Zobels and tweeter impedance compensation
are useful for odd order parallel c/o networks, and
even order series c/o networks.

For even order parallel and odd order series it should
be carefully considered if they would serve any point.

Regarding the Zobel on a subwoofer, pointless IMO,
unless a first order parallel passive c/o is being used.

sreten.
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Old 16th March 2004, 08:19 AM   #7
Svante is offline Svante  Sweden
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I agree with Sreten. Zobels appear particularly useless when no passive crossover is used. I haven't thought of it in terms of odd and even order filters before, but I think you are right about this too, Sreten.
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