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Thread: What does an inductor do in a speaker crossover?

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  1. #1
    Join Date: May 2008

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    Default What does an inductor do in a speaker crossover?

    I always see 2 spools of wire inductors in every cross over what do they do,I also noticed they are almost always next to a resistor.
    Jeff :UBERTHREADKILLER

  2. #2
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    Low pass filter.
    Sometimes they have a resistor in circuit to stabilise the speaker drive unit impedence.
    Chris



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  3. #3
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    Quote Originally Posted by Stratmangler View Post
    Low pass filter.
    Sometimes they have a resistor in circuit to stabilise the speaker drive unit impedence.
    I'm still not getting it,you mean it filters out low frequencies?
    Jeff :UBERTHREADKILLER

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    Passes them on.
    Chris



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    In the case of an inductor feeding a bass/mid it rolls off the treble. An inductor has a property known as inductive reactance & effectively what this means is that the resistance of the coil of wire increases the higher the frequency goes - so it rolls off the treble because it's in series with the bass/mid!

    In the case of a tweeter it will be in parallel with the tweeter & as it's resistance increases with frequency it will tend to shunt less power to ground the higher the frequency goes In co-operation with a capacitor this will increase the power to the tweeter as the frequency increases.

    Resistors are generally on the tweeter side as these tend to be a bit more efficient than bass/mids
    Bests, Mark



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  6. #6
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    Ok,so inductance creates the roll off,I always thought caps did that.
    Jeff :UBERTHREADKILLER

  7. #7
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    Caps are hi-pass.
    Chris



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    Capacitors do the opposite Well no, they do create a rolloff but in the opposite sense

    Capacitive reactance as it's known creates a reducing impedance (resistance) with increasing frequency.

    So imagine your bass/mid again, it has a choke (inductor) feeding it in series & a capacitor shunting the driver. As frequency increases the choke will increase in its AC resistance & the capacitor will decrease in it's AC resistance - it creates a steeper rolloff

    In the case of a tweeter being fed in series from a capacitor & having an inductor shunting it you get this... As the frequency decreases the capacitor displays more AC resistance thus rolling off the power to the driver & the inductor also has less AC resistance also creating a steeper rolloff..
    Bests, Mark



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  9. #9
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    It seems a miracle speaker crossovers work at all.
    What alot going on for so few parts.
    Jeff :UBERTHREADKILLER

  10. #10
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    Quote Originally Posted by goraman View Post
    It seems a miracle speaker crossovers work at all.
    What alot going on for so few parts.
    Jeff it gets worse as no drive unit has a fixed impedance, they all vary all over the place as well which can bugger up the crossover frequency & driver phase. As you can imagine this make things more complicated

    & just to make things even worse the driver sensitivity varies over frequency as well

    So yeah, it's a minefield out there



    This is why I like electronic crossovers as they are accurate. A whole lot of problems get left behind
    Bests, Mark



    "We must believe in free will. We have no choice" Isaac Bashevis Singer

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