Intelligible speech design requires direct sound to exceed reverberant and noise.

Evidence

The direct sound should be greater than, or equal to, the reverberant sound. This implies that the listener should be no further away than the critical distance. … The speech to interference ratio should, ideally, be greater than 10 dB n The previous two requirements have the implication that the level of the direct sound should be above a certain level, that is, at least 10 dB above the background noise and equal to the reverberant sound level. — David Howard, Jamie Angus, coustics and Psychoacoustics, 2478