Brauser - you are exactly right. The amount of power (watts) needed to give the impression of adequate sound pressure levels is less than you think. If the signal applied to your loudspeakers is not phase coherent, it will seem to lack "punch". If the listener then turns the volume up to achieve this "punch", it is only an attempt to compensate for the incoherent signal. What you end up with is a louder version of an incoherent signal. If you have a coherent signal then the "wattage" becomes more efficient. In other words if you have 2 systems, one coherent and one with phase or time domain errors, driving them both at exactly the same measured wattage, the coherent system will sound noticeably louder (at least 3+ db). Timing is everything.
Roger
Roger