The absorption values for the materials shown here are also based on a specific example of each type, and for a specific mounting method, they cannot be generalized across all materials of this type. Room shape will also affect the speech intelligibility, as focusing surfaces and late reflections will dramatically degrade speech intelligibility, as will exterior or interior noise sources. It would be a very bad idea to stretch these assumptions to cover a specific application of your own, as large errors would be possible. Problems with many variables, such as predicted acoustical and sound system performance, cannot be generalized effectively. Real live loudspeakers tend to vary significantly from theory, and one manufacturer's 90x40 loudspeaker is not often the same as another's.
Loudspeakers also vary widely in directivity with frequency.
Where a speaker may actually have a Q of 12.8 at 2kHz, it is likely that that the directivity value would drop to a Q of 4 at 500Hz, and as low as a Q of 1 at 125Hz. A thorough acoustical and sound system design would include the prediction of expected sound system behaviour across the entire audio bandwidth, taking into consideration the variations in loudspeaker coverage and variations in reverberation time. This is where computer modelling is very handy. Also note that with loudspeakers, more is not necessarily better. In very reverberant spaces, adding more loudspeakers can dramatically reduce intelligibility.