speaker sensitivity vs. speaker size

Depends totally on the impedence curve of the speakers. Usually the lower the impedence curve dips the more difficult the load. If you have a high current amp it won't make any difference.

Newbee (despite his name) is pretty much on target here. (Though I don't put much stock in the phrase "high current amp." As used by amp manufacturers/marketers, it can mean almost anything.)

The number of drivers is not the important factor here. Sensitivity is a measure of how loud a speaker can play with a certain amount of juice flowing through it. Based on the numbers you give, the floorstander will actually play a bit louder. (This assumes that both manufacturers tested their product's sensitivity the same way, which you cannot be sure of. That's why comparing specs is futile.)

Bomarc,

Mocking my moniker eh. Ah, whats in a name. A rose would smell the same (Forgive me Shakespeare for I haven't got a clue). Maybe I should just change it to Middlebee or Oldbee, but then it wouldn't bee as much fun. This way I get to catch some people asleep some times.

I thought you were just being humble!

A perfect example of this would be a pair of Revel M20's against a pair of B&W N803's. I had experience with this this past weekend. The Revels are far more inefficient than the 803's. The 803's are far larger in size and have double the amount of drivers.

This may help:
a gain in 3db of sensitivity will = double the wattage
a gain in 10db = double the perceived volume
Therefor, 100 watts on 86db speakers will be no louder than a 20 watt amp driving 94db speakers. That's why a lot of SET tube amps are only 5-10 watts.

The other thing to know is that most speakers are rated at a "nominal" rating for impedance and efficiency. Some will change a lot when driven really hard in the bass region. Therefor, a tiny speaker may be harder to drive since you are trying to get lots of bass out of a 5 or 6 in woofer vs a 10 or 12 inch woofer that is working less hard.

Loose -

Typically, the efficiency of the woofer sets the overall system efficiency.

And there is a trade-off relationship between bass extension, efficiency, and small box size - you can have any two of the three, but not all three.

Suppose you make a nice little 6.5" two-way mini-moniter. In order to get a good tonal balance, you might have to pad the midrange level down a tad, because the relatively small midwoofer is probably a bit weak in the bottom end. This lowers the overall system efficiency, but subjectively gives you a more balanced sound.

Now if you add a nice 8" woofer to do the bottom end, the midwoofer doesn't need to be padded down in the midrange any more. So the overall system efficiency can go up a bit without sacrificing the overall tonal balance.

This might be why the 6.5" two-way mini-monitor has a slightly lower rated efficiency than the 3-way floor-stander version.

Usually, a speaker's impedance curve is most challenging in the bass region. Without knowing the impedance characteristics of the 8" woofer and the 6.5" midbass driver, it's impossible to reliably predict which would be the "easier" load.

Duke