Speaker specs: Sensitivity, & Amp match

Can some help me with this question?
I am purchasing B&W speakers and the specs state the following...

Sensitivity 90dB spl (2.83V 1m)

What does this mean and what should I look for as I examine amplifier and preamp specs (as it relates to sensitivity).
I'm sure someone will give you the more 'tech' explaination. Actually the impedence spec is more important.
92 sen. sounds like an easy load; but not if the impedence drops down to 4 ohms.
Then we get into such variables as tube or SS power. LARGE room at LOUD listening levels????
Go long on the power; 'just barely enough', won't cut it.
Most speaker MFGs have a spec: power requirement---Say 100/300--- 100 being the min. and 300 the max. Look up what B&W recommends.AND,get more than the min.
Yes also consider the efficiency (impedance curve vs. frequency). Higher, benign loads are easy for amplifiers to drive. The sensitivity at dB/m/2.83V doesn't tell the whole story.
90 db at 1 watt, at 1 meter from the speaker is how loud it will be. To carry that further:
2 watts will equal 93db
4 watts equal 96db
8 watts 99db
16 watts 102db
32 watts 105db
64 watts 108db
128 watts 111db
110db is THX level, 112db is ultra THX
You have to increase 10db to double the perceived volume.
90db is decently efficient and should be able to be driven by almost any amp over 5 watts.

Impedance is another story. Check to see what the nominal impedance is. And then see what the minimum impedance the speaker will draw is. You can then set the amp for whichever is best. If I have 8 ohm speakers that drop to 7 ohms, I would probably set the amp to 8 ohms. However, if the speakers drop to 5 ohms, you should use either 4 or 6 ohms taps. You will not hurt the amp by setting it to a lower impedance buy may cause problems the other way around. The problem here is that it will sound better the closer you can set the amp to match the speakers.

Finally, in this long note, many solid state amps will increase power output greatly as you decrease impedance (ie 100 watts @8ohms, 150 watts @4ohms). Many tube amps will put out the same power regardless of impedance.
Elevick, I could be wrong, but I'm pretty sure to double the perceived volume, an increase of 6 db is needed. Can anyone else confirm this?
I'll eat my shorts if I'm wrong!
Elvick, I think you are safe - the word is percieved and we all percieved differently. Your post coincides with my perception, therefore you are right! :-)
S7horton is correct:)! 6db (spl) *is* "twice". Elevick: You show this yourself quite explicitly, above: As change in spl relates to w change^2, 2x as loud requires 2^2=4x watts. Every 6 db you clearly show x4 watts. Cheers!
Gregm, I think I'm getting confused! As I understand it, a doubling of power results in a (measured) 3db response in sound from a speaker, but the 3db, or even 6db, increase in volume isn't necessarily "percieved" by the listener as a "doubling" in volume. From what do you conclude the 6db increase in volume results in a "percieved" doubling of volume to the listener?
I smell this thread getting caught up in semantics.

But I do "percieve" myself having twice as much fun reading it than anyone else......:-)
Elevick is correct. A 10db increase in SPL will only be double the volume (what our ears hear and brain perceived to be).
The usefulness of all this becomes becomes apparent when we think about how the ear perceives loudness. First of all, the ear is very sensitive. The softest audible sound has a power of about 0.000000000001 watt/sq. meter and the threshold of pain is around 1 watt/sq. meter, giving a total range of 120dB. In the second place, our judgment of relative levels of loudness is somewhat logarithmic. If a sound has 10 times the power of a reference (10dB) we hear it as twice as loud. If we merely double the power (3dB), the difference will be just noticeable.

I actually thought the perceived increases were exponential, not logarithmic, but I'm far from an engineer. I just know my shorts will taste like s**t. Someone check audioasylum to bail me out please.
Keep in mind that I used the word "perceived" since I know a physicist will tear this statement apart otherwise.
Newbee: the difference lies in what you're measuring. If it's sound PRESSURE, 6db means "double" {20log10(p1/p2)=db}. When it comes to watts, 3db difference means double (or half, as it were).
Minimum "perceptible" diference in spl has been said to be 3db; if forewarned, I can detect smaller changes in spl, so can most of us.