Only the (0,1) kettle drum mode changes internal air pressure

Evidence

Since the whole membrane rises and falls together, the undesirable (0,1) mode is unique in that it changes the pressure as it oscillates above a plugged kettle, or in that it forces air in and out in a vented kettle. The higher modes do this less so or not at all, since they have about as much ”+” (orange) as ”−” (blue); they self-compensate, keeping the volume of the kettle steady. The air going in and out of the vent might be expected to preferentially dampen the (0,1) mode, but Rossing found that the vent hole does not contribute much to this damping. — Eric J. Heller, Why You Hear What You Hear- An…, 1413

Categorization

• DEFINE: Explains why ‘self-compensating’ higher membrane modes keep kettle volume steady while the monopole (0,1) mode does not — a key mechanism for the reader’s why-do-we-hear question.