Confining a vibrating source makes it radiate louder sound

Evidence

Imagine a piston forced to oscillate back and forth at a given frequency inside a chamber, which is connected to the outside through a small orifice (see figure 7.6). It is clear that if the piston oscillates fast enough, considerable excess condensation and rarefaction will arise inside the chamber, depending on the position of the piston, since the air will not be able to escape or enter fast enough to prevent it. Compared to the same piston in open air, the effort required to push against the excess condensation (higher pressure) and pull against the rarefaction (relative vacuum) would be considerable. Much of that is “reactive” force that returns energy to the drive, but some of the extra energy will go into making sound, now much louder than in the case of a free piston. The loading and the extra work imposed on the drive mechanism are in this case quite palpable. — Eric J. Heller, Why You Hear What You Hear- An…, 538

Categorization

• DEFINE: Gives the concrete mechanical picture of how loading a source (chamber + orifice) converts extra drive work into louder sound — the chapter’s core causal mechanism.
• QUESTION: The piston-chamber model is the basis of the Edison gramophone caption; worth tracing how this same loading principle explains why loudspeakers use enclosures (ported boxes) rather than bare drivers.