"I am always suspicious of speakers with multiple drivers."
Can you explain what you mean by this?
"Would you say that three is enough even if the room is big and you sometimes play loudly?"
I’m not really inclined to single out the number of drivers as something to focus on. I would be more interested in what the designer is trying to do, and how he goes about doing it, which in turn may or may not call for a particular number of drivers. I suppose there is some correlation between number of drivers and how loud a system will go, but the specifics of a given design matter far, far more than any generalities we might make regarding numbers of drivers.
Let me give an example of what I mean, pardon me from drawing from my own experience but at least this way it isn’t some arbitrary hypothetical: In my opinion, two worthwhile design goals are, good re-creation of the timbre of instruments, and good dynamic contrast. That’s "what I’m trying to do."
The "how" part is, I use driver combinations that a) give me a radiation pattern that is fairly directional and fairly uniform over most of the spectrum; and that b) have about 10 dB of excess thermal power handling capability above whatever in-room peaks we would normally expect. To get more specific, I use prosound drivers, with the high-frequency section employing a constant-directivity waveguide. The woofer crosses over to the waveguide at the frequency where its radiation pattern has narrowed to match that of the waveguide. (A "waveguide", in this context, is a type of horn, designed with pattern control and low coloration as the priorities, rather than acoustic amplification.)
The "why" part is, getting the reverberant field to have the same spectral balance as the first-arrival sound supports good timbre; and if the drivers are only seeing about 10% of their rated power on peaks, they will usually have negligible thermal compression, so the dynamic contrast on the recording is preserved. These aren’t the only things I care about of course, but they’re high on the list.
How many drivers does it take to do what I just described? In this case it would take two to do it pretty well and four to do it even better, and I’ve been known to use more than that, but what would the number of drivers tell you if you had no idea what they were or what I was trying to do? My point being, it's the SPECIFICS of a given design that matter most.
Duke