Reflected sound waves interfere with direct waves to create frequency peaks and dips

Evidence

The direct sound and the sound reflected off the ground interfered, enhancing certain frequencies at the expense of others. Reflections arriving from walls are indeed examples of such repetitions, and depending on their time delay and amplitude, they will cause peaks and dips in the received spectrum. — Eric J. Heller, Why You Hear What You Hear- An…, 2548

Categorization

• XREF: Directly connects the earlier repetition-pitch material (the jet airplane example) to room acoustics — a payoff moment in the reader’s why-do-we-hear question.