Impedance

--- For a resistive source and load, model your source as a voltage source in series with a resistance and your load as a resistance to ground. Your circuit then becomes a simple voltage divider:

Vs | [Rs] | +--->Vl | [Rl] | GND

Where: Vs is the voltage source Rs is the source resistance Vl is the voltage appearing across the load Rl is the load resistance

And can be described by:

Vs * Rl Vl = --------- (1) Rs + Rl

--- Charge gets transferred, But it's voltage that pushes it around.

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--- What what exactly mean?

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--- The longer the cable, the higher the capacitance, so the lower the capacitive reactance and the greater the loading on the source (generator) as frequency increases:

Vs>---[Rs]--->>--+--[Rc]-->>--+---Vl | | [Cc] [Rl] | | GND>--------->>--+-------->>--+---0V

Rc is the resistance of the cable connecting the source and the load,and Cc is the distributed cable capacitance shown as lumped, so Rc and Cc form a low pass filter with the reactance of Cc shunting high frequencies to ground.

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--- If it's a passive dynamic microphone, yes. If it's active, It may be AC riding on DC.

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--- The microphone is simply a generator sending a signal to the load and instantaneous values of the signal can be described by equation (1) if the system is resistive.

-- John Fields

When a source(e.g.Mic or guitar)is added to load (Mic Input),how does the source become affected in transferring its signal? I believe that circuits work as voltage transfer rather than current transfer. What this exactly mean and why do we have things like high-F rolloffs when cables are too long in unbalanced systems? Is Mic output A/C seeing that it's a magnet? How is the voltge "understood" by the load input?

Thanks

You may be only interested in the voltage from a source, but before that voltage can swing across cable capacitance, that capacitance must be charged twice a cycle by current from the source. The impedance of the source tells you how much current it can deliver before its output voltage gets loaded down by a given amount. For instance, if it is connected to a load impedance equal to its own, its output will fall to half of the unloaded value. High impedance sources work fine when connected with short wires (low capacitance) to high impedance amplifier inputs. But if you want to drive high cable capacitance without having that capacitance act as a low pass filter, you need to get the source impedance lower than the impedance of that capacitance. One way to do this is to put a step down transformer at the source to lower its voltage while increasing its current capability (lower its impedance). Amplifiers with so called "low impedance" inputs are just ones with higher voltage gain to compensate for the voltage step down.