Early strong versus late weak echoes dictate spectral fluctuation character

Evidence

As we have seen, the open wedge has a few strong early reflections and none thereafter. A large enclosed space with the walls and other objects a considerable distance away would have no early echoes, but a myriad of later, weaker ones. Clearly, the power fluctuations would be very different in these two cases, with the latter having more rapid fluctuations as a function of frequency. — Eric J. Heller, Why You Hear What You Hear- An…, 1162