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Help me understand Zobel

Discussion in 'Amps and Cabs [BG]' started by SeayBass, Jun 4, 2017.

  1. Hi all.
    Please help me understand Zobel Networks. I have read a bit on talkbass and many other sites- mostly forums- about zobels, and realize I don't know enough. I do understand that Zobel networks assist us in getting our crossover filters accurate. I have read many folks say that they don't affect the sound of a driver. I have also read several others who say they do. I am sure they do something to the sound, since they're added components. And I can hear it.

    I have put zobels on woofers and hear that it does tame the spike at the top of its range. For example, when I put a zobel on Kappalite 3012LF, I can hear that the spikey ~2kHz is less spikey. I have recently tried the same thing with the Kappalite 3012HO and heard similar results. Is this because the flattening of the impedance rise with frequency affects the output of woofer respectively?

    So I would like to know- are Zobels are bad for an amp?
    Has anyone else used them in this fashion?

    I am not well educated when it comes to audio electronics. You're invited to expound. Especially if I'm going to blow something up!

    thanks in advance
  2. Until the design engineers show up (I'm just a technician) here is my simplistic idea of what I think happens.

    A speaker voice coil is made up of a lenth of wire.
    A lenth of straight wire will have a very small inductance value.
    It will also have some resistance value because no conductor is lossless.
    If you wind the wire into a coil, as is done for a speaker's voice coil, the inductance increases significantly.
    The resistance of the wire however remains the same.

    If you apply a DC current, like a battery, to the coil, the inductance will have little affect on the circuit.
    The main affect on the circuit would be the resistance of the wire.
    However, if you apply an AC voltage to the coil, (audio is a form of AC) the inductance comes into play.

    At a certain constant frequency, the inductance in the voice coil will present a certain amount if reactance. Reactance in an AC circuit is very much like resistance in a DC circuit. It opposes current flow. The amount of reactance is dependant on the frequency applied to the coil. So you can see that audio, applied to a speaker will cause the reactance to vary as the frequency changes. This reactance contributes to the impedance of the speaker as seen by the amplifier.

    Amplifiers work best if the impedance they see is within their designed operating range.
    So if the reactance changes with frequency and that affects impedance, and that is affected by frequency, a speaker operating at a wide range of frequencies will present a wide range of impedances to an amp.

    In an AC circuit, a capacitor reacts to AC voltages in the opposite manner than that seen by an inductor.
    Thus, so does the capacitive reactance. While the reactive component of one is increasing with frequency, the reactive component of the other is reducing. Together, they act to help balance out the impedance variations seen by the amplifier.

    So this helps the load on the amplifier to not vary over such a large range as it would without the capacitive reactance being there.

    Resistance acts to further dampen the peaks of the variations. The resistor in series with the capacitor acts like the resistance of the coil to keep the impedance swings in the capacitive circuit somewhat the same as the inductive swings which are in opposition to the capacitive peaks.

    Amplifiers prefer a purely resistive load, void of any capacitive or inductive components. At one frequency and one frequency only, the reactance of a capacitor and an inductor will be equal, but opposite and cancel each other out leaving just the resistive component. This never happens as a practical matter, at least not long enough to do any good.
    So the best we get is a the capacitive reactance always opposing the inductive reactance at some level. Rarely perfectly, yet still offering a more stable load to the amplifier than if it were not there.

    Last edited: Jun 4, 2017
  3. that is an excellent and very informative explanation. And I gather I should worry less for my amp with a zobel than without. I thank you kindly!

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