Power fluctuations persist because echo arrival times unevenly populate Fourier components

Evidence

With no outer wall, the wedge system in figure 12.2 is always above the Schroeder frequency, since the resonances are dense and overlapping from the start. Figure 12.3 makes it clear why the fluctuations persist. The sharp echoes fall unevenly in time, and any given Fourier frequency (the sinusoidal undulations in figure 12.3) might pick up more positive contributions (where the cosine is positive at the time of arrival of an echo pulse) than an adjacent frequency. The frequency f3 in that figure is such a case. This continues to happen even at very high frequencies—for example, the high frequency in figure 12.6 corresponds to a positive fluctuation in power. — Eric J. Heller, Why You Hear What You Hear- An…, 1161

Categorization

• DEFINE: Explains what the Schroeder frequency is and why an open wedge stays above it.