What makes a speaker sound great at low volume?

I think good speakers sound equally well at all volumes. At least, this is what I observe with my Thiel CS6 and CS3.6 ones. I can hear the same deepness and resolution at a low volume as at a high volume (given that the recording quality is good) from any angle including from the back of the speakers. I would not believe that a speaker with other behavior reproduces naturally enough a good quality recording. Loudness, tone and other artificial tools I think are extreme and non-efficient.