When matching the Impedance of an Amplifier's output stage to a set of Loudspeakers or to Headphones, is it best to make the match exact, or is best sound had from making the output Impedance of the Amplifier somewhat lower than the Impedance of the Speakers?

I guess the same question would apply to transformer coupling the drive stage of an amp to it's final stage. Do Amplifiers like a bit of a load to push against?

Thanks, Brian

Impedance matching maximizes power transfer, whether or not that optimizes the sound depends on lots of other factors, not least of which is what sounds good to you. But there are a few technical factors to consider.

Transformers modify the sound, to a greater or lesser degree depending on how good they are, but the greater the turns ratio, i.e. the more step up or step down, the greater the modification. There are lots of reviews of tube amps that say they sound best from the 4 ohm taps regardless of speaker, and that may be because transformer sounds good and the 4 ohm taps use the most turns.

The musical signal in your system is voltage, and while impedance matching maximizes power transfer it does not maximize voltage transfer. This is most obvious in a MC phono stage where the preferred loading is usually something like 10 times the cartridge impedance. So how the designer trades that off is yet another factor that determines how a component will sound.

And of course the fact that we're talking about impedance rather than resistance means everything is frequency dependent so what is happening at 20 Hz can be very different from what is happening at 200 or 2000 Hz.  

So there's a lot going on.

It was a great help ! Thank you very much for sharing this !