I'm really confused

[crash32]

I am going to listen to the B&W 683's in a few days and I am also considering the Axiom M80's, but I am really confused about the whole 4 ohm and 8 ohm stuff.

The M80's are rated at 4 ohms which means it will be harder to drive than a 8 ohm speaker..... I really have no idea what that means though. Does that mean that I will have to put 100 watts into the M80's to get the same sound/volume I could get out of a 8 ohm speaker with only 50 watts?

If that is totally not accurate (which I suspect), could someone please explain it to me!

[Mr Peabody]

Neither would be harder to drive exactly. A 4 ohm speaker will require more current from your amp, especially if it's not very stable and swings much lower then 4 ohm impedance. A true "high current" amp will typically double it's power rating into 4 ohms. How loud you perceive the volume from the speaker has more to do with the speaker's sensitivity. If you intend to use a receiver a 8 ohm speaker will be safer and easier on it. The Onkyo may be alright with 4 ohms.

If a receiver driving a 4 ohm load without being fully capable it will run hot and when it's not able to produce the required current go into protection.

[blackraven]

Is your receiver the Onkyo 705? If it is, then it its rated for 4ohm speakers although it will not come close to doubling its power output as you only see that on more expensive equipment like my adcom which is rated at 145wpc at 8ohms and 268 at 4ohms.
Check the manual, I bet there is a switch or setting that you have to set to 4ohm which will limit the power output so that the receiver does not over heat and shut down.

Dont be affraid of 4ohm speakers but make sure that they are efficient and have a high sensitivity. One last thing. If you are considering running 2 sets of speakers for HT use, your receiver may not be able to run 4 speakers at 4ohms unless specified.