Basic question about sensitivity

Sensitivity is the efficiency of the Loudspeaker . Having modified alot of Loudspeakers ,the size can have something to do with it as well as drivers and 

most of all the Xover  and how complex it is. It’s always better to have more power ,

for in transients if youare playing loud peaks can go up 10 times that for 

a short fraction of a second and the amplifier can clip or distort which isnot good forthe drivers if a speaker says15 watts that’s minimum it is not full range 

and too what is the speakers capability ,in bass ? Many companies stretch the truth  there is no standard ,a speaker can say 38 hz but it maybe at + or -  6 DB which in truth speakers start to roll off earlier then the rated specs ,a good review will show 

a waterfall plot in how linear it is , I was watching and reading a Perlisten speaker review. They are very linear ,not many dips at all  , that’s why allways buy quality 

and as much amplifier you can afford to have overhead , more so if you are playing 

constantly over 85 db spend $30-50 on a good SPL level meter to see how loud 

you are playing . I have a Dynaudio speaker it says 87 db But it can dip down to 3 ohms which is pretty demanding I have shut down a 100 watt amp and my speakers are a 4 ohm loud I went to a amplifier that doubles it’s rating 150 8 ohms 

300 wpc at 4 ohms .  

on highly sensitive speakers, you can blow on your glowing tubes and hear wind from speakers, but on the good side all you need is quarter watt. 

On my experience, the size of the room & the volume you like to listen at have a huge impact on how much power you need for your speakers as well as their sensitivity. If you think about, the word “volume” applies both to the amount of db a speaker outputs as well as the cubic footage of the room. 
 

As Audioman58 pointed out, musical peaks,  both in the bass & lower midrange, can can easily demand 5- 10 times instantaneous peak power. I listen regularly in a large room ( over 6000 cubic feet) at volumes in the lower yo mid 90’s db’s & my 98 db sensitive Volti Rivals are barely using a few watts as indicated on the watt meter on my amp but when a loud peak comes, that can jump to 20 - 30 watts for a split second. 
 

Btw, I’m sure many of you folks are not horn loaded speaker fans but if you like your system to easily boogey on any kind of music & sound rich, detailed & not hard without really breaking a sweat, check out Volti’s! As Greg Roberts says - “have fun!”. 

OP,

Thank you for the question, I have had the same thoughts. I have four speakers:

(1) Thiel CS 2.3 - 87 db at 4 ohms

(2) Old school 1980s Infinity Reference Kappa 7s - 88 db at 4 or 6 ohms (don't understand the two values there)

(3) Buchardt Audio S400 MKIIs - 87 db at 4 ohms

(4) Clayton Shaw Caladans (on order) - 93 db at 4 ohms

I've never really understood the relationship between sensitivity and impedance, and how that translates into "easy or difficult to drive". Furthermore, how does that translate into the proper speaker cable: length, type of material, cable gauge, etc. It's never been an issue for me (that I've noticed), as I never listen to music at LOUD volumes....though I'm sure there is more that I should be paying attention to.

Also, why have I been drawn to the sound (except for the Caladans which I have never listened to in person) of 4 ohm speakers? Is it chance, or something more to it than that? It would seem on the surface, that I've ended up with speakers that are not the easiest to drive

It simply means that at one watt of power a speaker will produce the given amount of decibels. A flea watt amp will drive those Harbeth’s just fine, but it may not get loud enough to work in larger rooms.