This limits the distance you can communicate before speech is masked by the reverberant sound. If you could increase the amount of sound that was directed towards your target, and at the same time reduce the amount of sound that went off in all directions to add to the reverberant field, you could increase the distance you could communicate. This is what increased directivity does for you. Unlike the outdoor case we described above, where the unused sound is lost forever, in a reverberant space the unused sound bounces around and adds to the background noise. A high directivity source, like a voice through a megaphone, can significantly increase the effective communication distance.
Loudspeakers have to be selected on the same basis for use in reverberant spaces.
This is part of the sound system design process for us, we evaluate the reverberation time of the space, and determine what the directivity of the loudspeaker has to be to communicate over the distances required. It is possible to have reverberation times so long that it is impossible to select a directional enough loudspeaker to work effectively. The situation is complicated further if there are several loudspeakers involved. The loudspeakers that don't point towards you just contribute to the reverberant field you hear, without contributing to the useful sounds you hear. In very reverberant spaces, where one speaker may have worked, adding four or five speakers may prove to be unworkable.