Loudspeakers need enclosures to stop back-wave cancellation of sound

Evidence

Figure 7.27 Simulation of the effect of a loudspeaker enclosure, which acts as a baffle, preventing short-circuiting. On the lower left, the inset shows a speaker cone floating freely, moving to the right. A zone of compression (orange) precedes it, and a zone of rarefaction (blue) trails behind. The moving speaker cone has created a “dipole” pressure field, which favors certain directions over others and reduces overall sound intensity. When the speaker is baffled with a full enclosure, as shown on the right, the partially canceling, out-of-phase wave from the back is removed and the sound is much louder in front of the speaker. The enclosure confines the rarefaction (and when the speaker cone moves to the left, it confines the compression), allowing the rarefactions and compressions outside the enclosure to propagate without interference from an out-of-phase companion source. This is the main reason loudspeakers are constructed with enclosures. — Eric J. Heller, Why You Hear What You Hear- An…, 617

Categorization

• XREF: Directly answers why-questions about how speaker design shapes perceived sound.
• ADDENDUM: Relevant to loudspeaker/baffle physics that could support the trees-as-infrastructure piece by analogy (enclosures as directing flow).