A rigid wall raises the impedance of adjacent air cells

Evidence

The restoring force that any given cell presents upon being pushed on one side depends on how much pushback it receives when it tries to bulge out on the other sides. If one side of the cell is up against a rigid wall, the pushback from pushing on any other side will be higher, since one side can’t move at all. Thus the presence of the wall causes an impedance change. — Eric J. Heller, Why You Hear What You Hear- An…, 93

Categorization

• XREF: Connects to how closed-end tubes and organ pipes behave differently from open ones; boundary conditions in acoustics.