Doesnt resistance mean same as impedance??

Okay, Okay - we get it now:

'Resistance opposes Flow'

'Impedance rejects change'

Therefore:

Remocrats - go <against> the flow

Depublicans - impede all change  

and somewhere in there is a Phrase Change function too....

{ducking...}

Jim

In simple electronic models, a resistor is considered perfect as is a capacitor and an inductor. In practice, they all are flawed and have small elements of each other in their behaviour. For example a simple inductor can be a coil of wire, but obviously a length of wire has resistance.

Impedance is the real-world aspect of a circuit made up of resistors, inductors and capacitors. It accounts for e.g. voltage and current not being always in phase. In domestic audio, the measurement is encountered most reliably when describing loudspeakers with passive crossovers.

Impedance is resistance under load.

"There is NO frequency with DC, which is WHY, "resistance is constant".

The above is NOT true. You can still apply AC to simple resistance and its resistance will still NOT change, whereas a capacitor and/or an inductor’s resistance WILL change with AC.

Here is a table which shows how various components will respond to application of AC or DC voltage:

                  Resistor                            Inductor                    Capacitor
-----------------------------------------------------------------------------------------------

DC             constant R                        transient                   transient

AC             constant R                        varying R                  varying R

It seems many of these replies may be a bit more complicated than the OP is interested in. Both resistance and impedance are the opposition to current flow. Both are measured in ohms. The difference is resistance is a function of direct current electricity (DC) and impedance is for alternating current (AC). With audio components we are dealing with AC. For someone wishing to properly match components there are three main connections of concern: phono cartridge into phono pre-amp, system pre-amp into power amp and power amp into speaker. Ignoring the can of worms of cartridge loading, the input impedance of a power amp wants to be at least 10X the impedance of the pre-amp output for proper signal transfer. Most good pre-amps and amps easily meet this and so can, largely, be ignored. Speakers are another story. Yes, impedance does vary with frequency. In speaker measurements we see graphs of frequency vs. ohms. The speaker impedance will often vary from 4 to 20, or more, ohms. It is the lowest value we care about. Some power amps will have a hard time driving speakers that dip too far below 4 ohms because they cannot provide enough current and will get hot, distortion will rise and, in extreme cases, output transistors can be damaged. If you are considering speakers that get down to two ohms or less make sure the amp is capable of driving low impedances.

A final note of caution is if one is considering setting up two stereo amps in bridged mono for the increased power and reduced distortion, understand that a 4 ohm speaker looks like 2 ohms to an amp in mono and should only be done with speakers which do not go below 8 ohms.