Very early reflections can resonantly boost power across the whole audible range

Evidence

There is an important practical question regarding the average power: what if there are very early reflections, returning in such a short time Δt that the frequency smearing interval Δf = 1/Δt required to average out the resonant enhancement is very large? The average power theorem technically applies, yet the frequency averaging interval Δf may be larger than any frequency of interest. For example, if the reflections come back from a centimeter away in air, the consequent proximity resonance extends over much of the range of human hearing. For practical purposes, the baseline impedance and power has indeed been resonantly enhanced over the whole interesting region. — Eric J. Heller, Why You Hear What You Hear- An…, 1093