If the 91dB mentioned above is the sensitivity, then all that speaker needs is 1 watt to produce 91dB sound level at 1 meter. So there's no surprise that a 12 wpc amp can and will sound loud (clear is a subjective term) enough in a moderately small room. Other factors, which one could argue that are more important, are the speaker's efficiency as well as the way its impedance behaves across its frequency spectrum. Throw a piece of content with wide dynamic range and lots of transients, something like a large orchestral western classical music content, and the weaknesses become glaringly clear. Vocals, single instrumentals, and small bands like jazz trios, etc., not so much.
