What really IS impedance..........

[John_C]

I have a basic knowledge of electricity from A level physics.......capacitors, transformers etc..
But impedance seems like a whole other business, lots of maths, complex numbers etc.... Is there a simple guide anywhere on the net that really explains impedances and practical application with respect to audio gear?
If not, is there anyone who could explain it to me?

 

[Torniojaws]

Impedance = resistance of AC circuits.

impede
v 1: be a hindrance or obstacle to; "She is impeding the progress
of our project" [syn: hinder]
2: block passage through; "obstruct the path" [syn: obstruct,
obturate, occlude, jam, block, close up] [ant: free]

 

[Slemmu]

There might be something useful on these articles:

http://www.soundonsound.com/sos/jan03/articles/impedanceworkshop.asp

http://www.wordiq.com/definition/Impedance

 

[JBroll]

The simple answer: it's the analogue to resistance for AC circuits.

The more complicated answer: learn a bit about complex numbers (and calculus with complex numbers) and we'll get to work.

Jeff

 

[Metaltastic]

So what's the difference between impedance and resistance? Or is impedance the measure of resistance?

 

[MT01]

To put it simply when dealing with DC circuits you are dealing with resistance and AC circuits you're dealing with Impedence.

Impedance (symbol Z) is a measure of the overall opposition of a circuit to current, in other words: how much the circuit impedes the flow of current. It is like resistance, but it also takes into account the effects of capacitance and inductance. Impedance is measured in ohms, symbol ohm.

Impedance is more complex than resistance because the effects of capacitance and inductance vary with the frequency of the current passing through the circuit and this means impedance varies with frequency! The effect of resistance is constant regardless of frequency.

The term 'impedance' is often used (quite correctly) for simple circuits which have no capacitance or inductance - for example to refer to their 'input impedance' or 'output impedance'. This can seem confusing if you are learning electronics, but for these simple circuits you can assume that it is just another word for resistance.

Four electrical quantities determine the impedance (Z) of a circuit:
resistance (R), capacitance (C), inductance (L) and frequency (f).

For more info see http://www.kpsec.freeuk.com/imped.htm

All this takes me back to my college days, however my memory is very hazy!

 

[JBroll]

So what's the difference between impedance and resistance? Or is impedance the measure of resistance?

MT01 did it well - impedance is to AC (for our purposes) what resistance is to DC. In my overly silly lemming analogy a few months back, resistance was whatever made it harder for lemmings to jump off a cliff; if, instead of jumping off a cliff, the lemmings were bouncing back and forth with bungee cords, impedance would be the tendency of the bungee cords to 'lose' a bit of momentum.

Jeff

 

[Sloan]

fuck. i still didn't know that Z stood for impedance and was like WHAT THE FUCK IS HI-Z AND LO-Z, but now i know.

 

[Keiffer]

impedance is the response Capacitors and Inductors have to changes in either Voltage or Current. it is non-linear and time based whereas a resistor's response is linear and time independent.

A Capacitor does not allow instantaneous Voltage change and an Inductor does not allow instantaneous Current change.

because of this the Voltage and Currents are said to lag and lead.

for example: when voltage is placed across a capacitor with a series resistor, the current will initially assume I = V/R and the the capacitor will then begin to charge and current will decrease and the Voltage across the Capacitor will increase. the Voltage is said to lag the current. this characteristic is impedance.

 

[slashvanyoung]

fuck. i still didn't know that Z stood for impedance and was like WHAT THE FUCK IS HI-Z AND LO-Z, but now i know.

Don't let THEM fool you! It's Zignal!!11

 

[MT01]

Who's up for some Fourier and Laplace transforms?

*Gets coat*

 

[Keiffer]

Who's up for some Fourier and Laplace transforms?

*Gets coat*

S Plane... let's go

 

[Nebulous]

Correct me if I'm wrong, but I always remembered the simple answer to impedance vs resistance as :
"Impedance is frequency dependant resistance"

So resistance would be more a general term, while impedance was a specific term, hence why we would use it so often in audio.

 

[John_C]

Thanks guys, some very good info!
I'll get back to you when i've read all the links and understand them a bit better.

And Jbroll, I'll have a look at calculus with complex numbers for a fuller understanding, although i suspect it'll be well over my head hehe