This has been known for some time. Well before Toole assembled the key measurements into his single spin-o-rama test suite.
It sure has been known for some time. Here’s a bit from ATCs brochure ..
“4. Dispersion and Directivity
The relationship between direct and reverberant sound is very important in high performance loudspeakers. It is clear that not only must the on-axis magnitude response be accurate and linear but also that the behavior off-axis must be both broad and even with frequency exhibiting no abrupt dips in amplitude.The aim should be to achieve a horizontal dispersion of +/-80 deg. With a -6dB @ 10KHz and a vertical dispersion of at least +/-10 deg.To ensure that in a well behaved room with a good RT vs frequency characteristic,The reverberant sound will be consistent with the direct sound in the listening area.
To achieve this criteria the highest performance loudspeakers will be either small two way systems with bass/mid drive units up to 160mm diameter or preferably three way designs where the midrange is no more than 75mm diameter and crosses over from the bass drive unit at around 300 Hz. The tweeter in this system should not be greater in diameter than 34mm and should be crossed over from the midrange at around 3 KHz.
In a well behaved room when listening to a stereo pair of loudspeakers with a good relationship between direct and reverbant responses you will first hear the direct sound and then the reverberant field. It is generally agreed and probably true that the reverberant field masks periodic signals, however, it is also apparent that the ear has a precedence effect which means that for impulsive sounds the ear can hear phase dependent effects. Therefore, I believe that any critical judgment of repro- duced sound is made principally on the first arrival or direct sound which gives most of the phase related cues and also the low level detail which is quickly lost in the reverberant field.
However, the way we perceive magnitude band balance and the full energy of percussive or impulsive sounds, is dependent upon the power response of the loudspeaker or how evenly it excites the reverberant field with frequency.
Clearly it is impossible to exclude from such a relationship the effect of room acoustics, however, for the purpose of discussing loudspeaker performance we will assume that the listening room has been properly treated and has no serious intrusive acoustic problems.
It should also be stated here that the use of DSP to equalize loudspeaker room interface problems is not an acceptable solution to that problem in critical listening environments if it involves modifying the direct sound from the loudspeaker. A dramatic effect of poor midrange dispersion, common in many two way loudspeaker systems, is demonstrated by recording engineers making incorrect magnitude band judgments and applying equalization, usually to the upper midrange, in an attempt to compensate for the apparent lack of energy in that region. Many examples of pop recordings are available which demonstrate this characteristic. That is, a hard strident upper midrange which masks high frequencies, and makes vocals sound recessed while accentuating the bass.”