Quote Originally Posted by icarus
As for nominal impedance, what is it refering to and how would an impedance of 8ohms perform compared to 4ohms?
Let me emphasize the word "nominal" in that the stated value is for a single frequency or range only. Most speakers (with a few exceptions like Magneplanars) vary their impedance by frequency. The curve for some speakers looks like a roller coaster. This is important for amplifier selection. I favor tube amps, but because of their high source or output impedance, their frequency response can be affected by those roller coaster curve speakers. While my 'stats are kinda evil at the top, they exhibit a pretty smooth curve that does not vary radically from octave to octave. On the other hand, look at this speaker:

Roller Coaster

So, is this a 3 ohm speaker? 6? 12? 20? Solid state amps tend to work better with this kind of speaker to maintain a neutral response.

I agree with the opinion that neither spec in and of itself provides any qualitative information. They do provide insight to matching an amplifier to your chosen speaker. This topic is crucial and often overlooked. The "best" amplifier for one speaker may not be the optimum choice for another.

rw