Let's take this from a different perspective.

When Low Impedance feeds High Impedance, you have Maximum Signal Transfer.

When High Impedance feed Low Impedance, you have Maximum Current Transfer.

When an Equal Impedance feeds an Equal Impedance, you have Maximum Power Transfer.

One would think Max Power Xfer would be the idea, but it is not.

In the case of Audio Amps, though it may be obtained by artificial means, you want the Amplifier Internal Impedance as small as possible. You can get some sense of the Internal relative to External Impedance by looking at the Amp's DAMP FACTOR.

Amp with low Damp Factor tend to be exceptionally clear, but far less stable. Amps with High Damp Factor then to be very stable but less clear. Though we are talking relative terms here. Common amps have Damp Factors in the 100 to 300 range. Amps with Low Damp Factor tend to be less than 100, and I think I might have some Amps where it is 50.

What a Damp Factor of 50 means is that the internal impedance of the amp is 50 times SMALLER than the standard load. So, if the standard load is 8 ohms, then the internal resistance is 8/50 =* 0.16 ohms*, or if the Damp Factor happens to be 300, then the internal resistance of the amp would be 8/300 = *0.027 ohms. *

To understand why this matters, let's look at speaker wire. The higher the speaker wire Resistance, the more signal is lost in the wire, and the less is available to the speakers. Every time there is a surge in Current, the voltage across the speaker wire increases stealing more of the signal from the speakers.

The same is true with the Amps internal resistance, the higher is its the more signal it steals.

But, there is much more to the design of an amp than Damp Factor. So that one spec alone is not an indication of the quality of the amp.

I suspect though you might be alluding to whether the amp is 8 ohm rated as in ... *100w/ch to 8 ohms*. That is completely different. That is simply an amp whose power is rated to an international standard so all amps can be fairly compared to each other. When you find amps rated at 4 ohms or 6 ohms, that is simply an attempt by the manufacturer to inflate the seeming power. So, if that is what you are referring to, as before, that alone has nothing to do with the quality of the Amp.

I have a Amp that was low cost, about £175, that has a Damp Factor of 50, and it is very clear, but doesn't seem to have the weight of my other amps. My second amp is Damp Factor rated at about 300 and cost about £400. My third amp also has a Damp Factor that is high, over 300 and it cost £1400. All are rated compatible with speaker loads in the 4 ohm to 16 ohm range.

If you want a more direct answer, you are going to have to explain what prompted you to ask this question. Or what is it you really want to know? Generally, while the question can be discussed, Impedance has nothing to do with the quality of the amp.

Now of course that assume standard quality amps. You might find an amp with a Damp Factor of 10, which would not be generally good, and while it will tell you something about the amp, it doesn't necessarily tell you if the amp is good or not.

Then we have *"Z" vs "R"*, generally we are referring to general Resistance. That's done for simplicity of conversation. In reality any impedance is going to be a combination of* Resistance, Inductance*, and* Capacitance*.

Resistance is always in-phase or 0 phase.

Pure Inductance is always +90° out of phase

Pure Capacitance is always -90° out of phase.

The "Z" or functional impedance is the vector some of all these components. It will have both Amplitude (voltage) and Phase Angle.

The formula for *Power is Volts X Amps, *so you would think they would be the same thing. But if you look and the voltage and power information of the back panel of your amps, it is always rated in VA* (voltamps)* instead of Power, because there is a Phase Angle involved and a simple *Volts X Amps* does not tell the whole story.

I suspect while informative, that does not answer your question, but I'm not actually sure what your question is or why you asked it.

One final point, informative, but not responsive to your question, Damp Factor can be artificially increased with the use of *Negative Feedback,* a small bit of the output signal is inverted and feed back into the input. Again, this is a delicate balancing act. It can make Amps more stable, but perhaps not sounding as good. Not having Negative Feedback can yield a smaller Damp Factor, and while the amp *might *sound better, it will be less stable.

We have to trust manufacturers to have made all this analysis, and made the best decisions for their amps within their design philosophy and price point. And within limits, we can trust the price and the brands reputation.

Keep in mind, I think if I looked long enough and hard enough, I would have no trouble finding amps in the 6-digit range, and perhaps, after a very long search in the 7-digit range. So us mere mortal who are in the 3 and 4-digit range will just have to settle for the best we can afford.

Steve/bluewizard