Exciting multiple room modes instead of one reduces frequency and spatial sound variation

Evidence

Because of this, the accepted definition of critical frequency is based on the mode bandwidth, although this can result in a chicken-and-egg situation at the initial design stages; hence the earlier equation. The rationale for this is as follows. The main consequence of modal behavior is the frequency and spatial variation caused by it. This means that if a given frequency excites only one mode, then this variation will be very strong. However, if a given frequency excites more than one mode, both the spatial and frequency variation will be reduced. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 2033