Sudden surface motion is required to produce an audible pop or boom.

Evidence

To make an audible pop or boom, the surface must jump suddenly, creating a sound containing frequencies in the audio range. Otherwise, only infrasound or very low frequencies, will be produced—too low in frequency for human hearing, or at least far too low to cause the sensation of a bang or pop. (Some of the small earthquakes in Moodus do apparently cause a low rumble.) — Eric J. Heller, Why You Hear What You Hear- An…, 695

Categorization

• DEFINE: Sets the frequency criterion for what makes a transient feel like a bang versus a rumble.