In a fairly small room (say a spare bedroom), two main issues arise:
1. The bass response will typically have major peaks and dips largely due to the room modes being few and far apart (an inevitable consequence of the room being small); and
2. The reflections above the bass region will arrive after an unusually short time delay because the reflection paths are quite short, so the result is a lot of energy in early reflections. Early reflections are the ones most likely to be detrimental to timbre and imaging, so in a small room imo it is especially important to take them into account.
There are techniques for addressing these issues, but some of them are highly counter-intuitive. Multiple subwoofers intelligently distributed can ime significantly improve the bass region, and using speakers with good radiation pattern control over most of the rest of the spectrum can improve the room interaction up higher as well.
In this context, imo "good radiation pattern control" implies a radiation pattern narrow enough that it can be aimed to minimize early reflections, and uniform enough within its coverage pattern that the reflections are spectrally similar to the direct sound.
This is a bit different from the typical approach of using "small speakers for small rooms and big speakers for big rooms." It is more like, choosing the acoustic behavior of the speaker system to deliberately address the acoustic challenges presented by the room.
Duke
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