Must speakers have certain volume to sound convincing ?

I think this very much involves the psychology of each person and thier listening habits and enjoyment. I like low listening very much. I also think planars give enough info at low volume for enjoyable sound. Just my opinion...
BTW even my neighbors Sonos speakers sound clear and fantastic at low levels. Not as much bass as my Monitor Audio Bronze but just as clear and articulate.

One hears with their brain not their ears. That was my point early on. We are all slaves to our experiences, education and preferences built over our lifetime.
Also it was mentioned "assuming good hearing". I would bet our hearing abilities across the frequency spectrum are all over the place...collectively. "When is the last time YOU had your hearing evaluated?" I agree with asvjerry. Also the set of preferences, qualities or the like ....with what sound should be is also different for everyone. Each of us will place a higher or lower value on such tags as "soundstage, dynamics, bass depth, etc"