What makes a loudspeaker "room friendly" ? I mean not perfect, nor perfect in every room, but well behaved in most of them
"Room friendly" is something I aspire to in my loudspeaker system designs, which imo implies that how the speaker sounds either does not change significantly as the room acoustics change, OR that the speaker has enough built-in adjustability to adapt to most such changes.
I agree with
@Inner Space's observation that the unusually narrow-and-controlled-pattern, bass-limited Klipsch LaScalas would be exceptionally "room agnostic" (and I like the term).
I agree with
@eddantes's suggestion of speakers which avoid directivity errors, which imo applies whether the speakers be wide-pattern or narrow-pattern or something else. You want the reflections to sound like the first-arrival sound, regardless of whether those reflections are strong or weak, and regardless of their arrival times. Personally I prefer narrow-pattern over wide-pattern for room-friendliness, to keep the early reflection situation from changing drastically as the room changes. Also in general the higher the direct-to-reverberant sound ratio, the less change from one room to the next.
Here are some of the characteristics I use:
1. An unusually uniform radiation pattern no more than 90 degrees wide (-6 dB @ 45 degrees off-axis to either side) over most of the spectrum, which can be aimed to avoid early same-side-wall reflections. These 90 degree patterns can be toed-in aggressively to criss-cross in front of the listener and thereby avoid significant early same-side-wall reflections, such that it no longer matters as much whether the side walls are acoustically symmetrical. One could certainly set up the LaScalas this way.
2. User-adjustable top-end "tilt". Rooms can vary significantly in how absorptive they are at short wavelengths, so some ability to adjust the top end can be helpful.
3. User-adjustable bass tuning via multiple pluggable ports, and/or (preferably) a separately-powered distributed multi-sub section for the bottom couple of octaves.
4. A somewhat adjustable direct-to-reverberant sound ratio, accomplished by having additional level-adjustable drivers dedicated to the reverberant field. The top-end tilt of these drivers is user-adjustable.
Personally I do not use either dipole or cardioid loading but several unusually room-friendly designs do, such as those from Gradient and Spatial and Dutch & Dutch.
In my experience fullrange dipole speakers which have unusually uniform radiation patterns (such as SoundLabs) are exceptionally room-friendly as long as they are positioned far enough out from the front wall.