What's with 4 ohm speakers?

They're not hard to drive if you have a good amp. Also, 4 ohms is an average. Depending on the frequency of the music you are playing, the speakers resistance will vary.

I'm just now reading through all this and have to apologize for my 1st post. Its really a half ass response, but I did it for a reason. As far as 4 ohms not being an average, thats my error. I always thought nominal meant average (in context of speaker impedance.) I also should have put an exception in for most tube amps and a few SS ones, as well.

When I read the OP, I couldn't make up my mind if it was an attempt by someone who doesn't like high end audio for some reason and just wants to start an argument, or possibly a beginner who just doesn't know. Its just a vague statement with no equipment or examples listed. Usually, when someone really wants to find out something, they do a little better with the specifics. Thats why I made the if you have a good amp comment. I just pictured a beginner with something like a Sony receiver possibly looking to move up. In that context, a typical entry level SS amp shouldn't have too much problem driving a 4 ohm load.

Unfortunately, it looks like I may be right. Everyone here is giving some really high quality answers and the OP is no where to be found. If it makes any difference, I read through all the posts and thought they were truly excellent.

"The statement is ambiguous. We know that doubling power is 3db, and that there is or should be a direct correlation with driver output. Since this is so then driver output is also proportional to power."

Wouldn't you have to take other factors into consideration like how the room interacts with the speaker, or possibly, the distance from the speaker to where the measurement is taken? Or is there some type of industry standard and everyone measures these type of things the same way?