Must speakers have certain volume to sound convincing ?

I agree with gdhal. The system needs to pressurize the room. For the mood, the song, day or night. Even low volumes interact with the ROOM. My small system needs a small room, Main system needs its own room. But my body wants a remote volume control for those needed/ wanted tweeks!! Plan to add one to my Steelhead shortly!

" Panels have no volume" What nonsense. My 3.6's can blow me out of the room and with the right amplification the dynamics are sensational. 
Alan

I agree with Alan about panel speakers. They can rock.
I use horn speakers which are known to be good at low levels, but even they need a certain amount of volume to be really convincing.

Besides what Mapman said I also meant internal physical volume of speakers.
Panels sound nothing like real music, as beautiful as they can do. They are for dreamers not for those who want to hear it as it is.
As for horns, it's a different matter.

All else held constant, in order to be able to produce flat response down to lower frequencies, you need larger drivers in larger rooms. In the case of "box" speakers you also need larger boxes ie more internal volume. I think its that simple.