# Capacitors in Audio Applications?

Discussion in 'Audio' started by SaintApoc, Sep 10, 2017.

1. ### SaintApoc

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May 1, 2017
I have an interest in audio but a hard time understanding how the electronics really work. I only took half a year of electronics when I was in highschool and that was over a decade ago.

When it comes to electrolytic capacitors, I have a general understanding that the hold a charge, can dissipate a charge, and are unidirectional.
I see in forums and spreadsheets that capacitors are used as a "filter" for frequencies, in that adding one will change what sounds are produced more readily by the speaker driver. I am curious as to why this is.

1. Audio signals are more or less AC, so wouldn't that mean the capacitor is being harmed by the opposing flow of electrons?
2. If a current is like an electron flow, wouldn't a capacitor be "filled up" and then act like a straight connection - as in, how does it filter if it is "full?"

2. ### kellys_eye

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Jun 25, 2010
Capacitors have 'reactance' which, for the sake of simplicity, can be considered as 'AC resistance'. The amount of resistance it offers to a signal is related to the value of the capacitor and the frequency applied to it.

Its' resistance (reactance) is given by 1/2.pi.f.C

where f= frequency (in Hz) and C is capacitance (in Farads) (pi is in apples )

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3. ### SaintApoc

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May 1, 2017
Oh my gosh, that makes a LOT of sense! Thank you so much!

4. ### dorke

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665
Jun 20, 2015

1. Anything that isn't DC(fixed in time), is considered AC.
So,Audio signals are all AC.

Electrolytic Capacitors polarity relates to the DC voltage element only,
no problem whatsoever with the AC element of the signal(if the DC element isn't negative).

2. When applying AC signal to a capacitor the nature of the operation in your terms would be:

momentarily filling-up(charging) at the positive part of the cycle ,
momentarily un-filling(discharging) at the negative part of the cycle.

The net would be "zero charge" on the capacitor in an AC cycle.

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5. ### SaintApoc

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May 1, 2017
Oh wow, this also makes a lot of sense! Thank you for simplifying it for my brain to handle - this helps a lot!