capacitance using the equation: 1/(2*pi*R*C) to caculate the low freqquency cutoff. The cap works as a high pass filter (more on that
here) Basically, its 2 plates that are very close to each other, and when a charge accumulates on one plate, it repels the charge on the other (like how magnets push each other away when orientated right, kinda). but once there's no more charge to push away, it stops.. so basically, it wont respond to a constant charge on one plate after a very short time, but will respond to a changing one. The main purpose that we use them for is to block whats called "Direct Current", which is basically the constant flow of electrons in one direction that would ruin things like headphones. this DC is a result of constand voltages that signals oscillate around in the reproduction of the analog signal from the digital data, bla bla bla..
Back to the equation
R- Resistance of the load. In our case, an amplifier, whos load on a circuit is equal to a resistive load of anywhere between around 10,000 and 100,000 Ohms.
C- The capacitance of the capacitor. A value that indicates how much charge can accumulate one one plate before it stops accumulating more.
So, for example, a 50kOhm load with a capacitor of 1uF would give us a cut-off frequency (the frequency where the signal is attenuated by 3db (basically means only half the power of the signal goes through, as the frequency gets lower, less and less of it gets through. 0hz (dc) wont go through at all) of:
Fc=1/(2*pi*R*C)=1/(2*pi*50000*0.000001)=~3.2Hz.
(Hz- oscillations per second)
so with a common amp, a 1uF cap would give a cutoff frequency of 3.2Hz which is well below what we can hear anyway. we chose such low values cause the cap will continue to effect frequencies above that, to a lesser degree as they're higher... and for flexability.
a 47uF cap would give a cutoff frequency of about 0.5Hz for the same load.. overkill, yes, but we use them cause its effective and cheap cause of the type of cap it is. some of the lowe values, like 1uf, can get really expensive.
Bottom line:
I broad range of caps is good for us, anything above 1uF will have favorable functionality for a broad range of amps.. and all caps behave a little differently, and sound a little different, and here the fun starts.. pick your cap and see how it works, enjoy the music!
P.S Picking the 'right' cap isn't always easy, either go with the flow or browse the forums.. too much to talk about here. Forum user dsavitsk shared his valuable experience
here which is worth a go over, imho.
hope this helps more than it confuses....