how can low watt tube amps drive speakers with higher power requirements


I am new to hifi and I am super confused about something. Most audio blogs out there ask newbies to stick to amps that output power within the recommended range of the speaker manufacturers. However, on forums, blogs and even some magazine articles, I find pros reviewing tube amps with much lower output power (even in some cases 10-30W below the speaker specs) and find no problems. How can these low power tube amp drive these speakers? For example, the LS 50 metas spec sheet says "Recommended amp power: 40W - 100W) but I have seen posts here and on other forums where people will hook these up to tube amps producing as low as 12W of power at 8 ohms. Am I missing something?
selekt86
So much of it depends upon your room size and how loud you want to listen.  Obviously the larger the room, the more power you will require to fill that room.  The same for high volume listening.  If you are using a smallish room and never go louder than 80dB, then you really don't need too many watts.  BTW, 80dB while not considered loud is too loud to have a normal conversation.  The manufacturer's suggestion is a generalization to cover a wide range of situations that may or may not apply to your particular case.
The answer is pretty much covered by the other responses here... the loudspeaker rating is how much power it will tolerate, the amplifier rating is how much power it is able to deliver. So you need an amplifier that can deliver the sound levels you want plus a bit of headroom to avoid excessive distortion / clipping.
One advantage of using a lower powered amplifier is that you don't need to attenuate the signal as much... potentiometers tend to perform progressively worse the more the volume is turned down, there's more information on that here if anyone's interested.
4 Watts drives my 92db Ref 3A de Capos just fine.  Not concert level but loud enough in a 12 x 20 room with openings on the side
KEF doesn't know what kind of amp or quality of amp you're going to use.  The figures quoted are no doubt within a "safe" margin, and were probably determined as much by lawyers as by technical people.  Experiments are good, but always at your own risk.
An inadequate amplifier is easily driven into clipping and the clipped output of an amplifier includes excessive high frequency distortion energy.  It is the clipped output that is the tweeter killer.  For that reason low powered amps lacking soft clipping are more dangerous to speakers than are higher  power amps just idling along.