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speaker sensitivity vs. speaker size

I would like to draw on all of you for your experience on this matter.

Here is my question:

If I have two pairs of speakers, one being a pair of monitors (bookshelf size) and a pair of floor standers (both from the same company, in this case) and they both have the same sensitivity rating (actually, in this case, the bookshelf is rated at 85db/w/m and the floorstander is rated at 86db/w/m), would they both be equally easy/ difficult amplifier loads (if the identical amp was used on either pair)? (sorry about the run-on sentence)

The larger speaker has a metal tweeter, a 6.5 inch midrange and an 8 inch bass driver. The smaller has the same, minus the 8 inch driver.

It is my inclination to think that, despite the ratings, the larger would be the more difficult load as it has more drivers to control).

I am calling on you guys to help with clarification on this matter.

thanks in advance
loose
s7horton
1,077 posts
 
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.
elevick
2,636 posts
 
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.
audiokinesis
2,737 posts
 
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
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