4 Ohm vs. 8 Ohm, what does it mean.....

It's a good question and typically misunderstood by many--even some designers. You are correct in thinking that the higher load would be more "accurate". It has less demands on the amplifier and is easier to drive. However, the trade off is that it has less output per watt that it's 4 ohm counterpart. For this reason many manufacturers reduce (or trade off) the load for higher output. In addition the load (4 ohm vs 8 ohm) that you are referring to is the "nominal" impedance of the speaker. Many speakers rated at 4 ohms can go down to 2 ohms at certain frequencies or even lower. This can create very difficult loads to drive and they can be very demanding on amplifiers. So, as someone once said to me after a lecture, "what's the take home pay?" These nominal impedances have little meaning. You need to see what the impedance curves are throughout the range and once you know these you can narrow down the amplifiers that might be appropriate for that speaker. A speaker with relatively flat impedance curves even if it's rated as a 4 ohm speaker will be easier to drive than a speaker that has wild swings through the frequency range.

also keep in mind that Tube amplifiers like higher impedences such as 8 ohms or higher, were as Solid State amps can drive more power into lower impedences such as 4 ohms. although even some of the best Solid State amps can still have trouble driving very low impedences such as 2 ohms. speakers that drop down this low I would stay away from because they will limit the choice of amplifiers you can use on them.

I absolutely agree with the above responses from artistic Audio and from Rives, The Manufacturers have focused on 4 ohm speakers to market them more effectively. They sound louder in the demo rooms than would an 8 ohm speaker at the same electronics setting. I suggest taking a sound level meter with whem auditioning speakers. Also bring your own music and don't rush the demo. Take your time and stop back a second time if necessary. Better yet, take the speakers home because the room is a big factor in the evaluation process. Good Luck

In almost every aspect, performance of an amplifier is "better" at 8 ohms that it will be at 4 ohms. Distortion is typically lower and more linear across the frequency range, bass will be more controlled i.e. "damped", less heat to build up or dissipate, etc...

Only problem is that higher impedances make it harder to transfer large amounts of power and current. While tubes can get around the power transfer problems as they tend to like higher impedances better, they still won't deliver the high current necessary to keep an "iron grip" on a woofer. If one can keep a reasonable impedance ( 6 - 10 ohms ) without a lot of reactive swings as frequency changes and do it with high sensitivity, you would pretty much have the perfect load for an amp. Whether or not the frequency response, transient response and dispersion characteristics of that speaker would work for you may be a whole 'nother ball of wax though : )

Unfortunately, many of the speakers that i personally like and own are both low impedance and low sensitivity. This makes for an up-hill battle all the way. There are only two cures for that i.e. either throw them out and buy different speakers that are a lot less finicky or run amps that are built like tanks. Guess which path i took ??? : ) Sean
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Sneaky follow on--what does it mean that McIntosh has always given its' ratings (even back in the 60's)at 2, 4, and 8 ohms? I assume its' a sign (guarantee?) of linearity. I run a 7270 and 7300.