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Old 5th June 2011, 06:08 PM   #1
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Default Best Place to Put a Zobel Network

Shall I mount the Zobel at the speaker or on the crossover board? Also I have seen networks that use inductor, capacitor, and resistor instead of just the capacitor and resistor. I am not sure what use they would have.
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Old 5th June 2011, 08:03 PM   #2
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An LCR vs a CR shunting filter are 2 very different things. LCR is a trap or notch that shunts to ground the nasties you have to avoid and/or remove. CR filters adjust the knee at the point of rolloff, smooth out the impedance of the driver on the upper end, or tilt down the response of a tweeter or mid.

A Zobel is a special-case CR filter. As defined, a zobel is used to flatten the inductive rise of the impedance in a driver. If the values differ from this method of use, then it is no longer acting as a zobel.

They both can serve differing purposes, but it depends on the method or place they are used.

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Old 5th June 2011, 08:25 PM   #3
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Thanks Wolf. Does it matter where physically the Zobel is positioned? At the driver or on the crossover?
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Old 5th June 2011, 08:55 PM   #4
Loren42 is offline Loren42  United States
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Originally Posted by swantzilla View Post
Thanks Wolf. Does it matter where physically the Zobel is positioned? At the driver or on the crossover?
As long as the wire between the driver and the Zobel is of low enough resistance it will not matter.
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Old 5th June 2011, 10:18 PM   #5
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I would put the zobel on the amplifier pcb.
A long speaker lead with have resistance and inductance.
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Old 5th June 2011, 10:42 PM   #6
Loren42 is offline Loren42  United States
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Originally Posted by nigelwright7557 View Post
I would put the zobel on the amplifier pcb.
A long speaker lead with have resistance and inductance.
Actually, you are trying to correct the driver's impedance curve, so, in an ideal world you would want it at the driver's terminals.

I would not expect any inductance in a speaker wire - unless you coil the wire.
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Old 5th June 2011, 10:46 PM   #7
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Actually, you are trying to correct the driver's impedance curve, so, in an ideal world you would want it at the driver's terminals.

I would not expect any inductance in a speaker wire - unless you coil the wire.
On the contrary the amp is the thing you are trying to give a flatter load to.
I have seen quite resistive speaker leads and like you say sometimes people coil them up. I run a mobile disco and can have upto 50 foot cables.
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Old 6th June 2011, 12:01 AM   #8
Loren42 is offline Loren42  United States
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Originally Posted by nigelwright7557 View Post
On the contrary the amp is the thing you are trying to give a flatter load to.
I have seen quite resistive speaker leads and like you say sometimes people coil them up. I run a mobile disco and can have upto 50 foot cables.
If I am reading the original post correctly, the speaker has a passive crossover.

In this case it's the crossover that needs to see a constant impedance.
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Old 6th June 2011, 12:04 AM   #9
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Originally Posted by Loren42 View Post

In this case it's the crossover that needs to see a constant impedance.
No, the zobel was designed to match the amplifier better to the load.
It gives a flatter load to the output transistors.

The crossover has to deal with speakers which are never a flat impedance.
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Old 6th June 2011, 12:27 AM   #10
Loren42 is offline Loren42  United States
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Originally Posted by nigelwright7557 View Post
No, the zobel was designed to match the amplifier better to the load.
It gives a flatter load to the output transistors.

The crossover has to deal with speakers which are never a flat impedance.
Well, that is not how I understood it. I can cite this website as a reference. If he is wrong I would like to understand why because I am in the midst of designing a two-way passive crossover now.

The link:

Passive Crossover Network Design

Look for the following statement in section 3.1.1:

"Once determined, the Zobel network must be treated as part of the loudspeaker. All measurements or calculations for the crossover network must include the Zobel network and loudspeaker driver combined. If correctly done, the combination of the two will give an acceptably flat and very usable impedance across the entire crossover region. This will result in a crossover filter with the minimum error possible."

I am reading that as the Zobel must be between the driver and the crossover network, which makes sense to me.
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