Originally Posted by
Asliang
Well the simple way to say is, impedence swing = harder for amp to drive in a certain frequency range (overload).
When amps overload, they give off an individual type of distortion. Tube amps give off even (pleasant, warm) order distortion, solid state give off odd (not so pleasant, harsh) distortion. I believe in if the orders are higher (say fifth vs third), it becomes more annoying even if the THD% isn't any higher. If the Panny has a really high order distortion, this might be the cause of the harshness, even though it only measures at 0.03% at 1W input.