A horn amplifies sound without increasing diaphragm motion

Evidence

As was stated in a scholarly paper by A. G. Webster in 1919, when such phonographs were still in regular use, “it is well known that very little sound is emitted by the phonograph … with the horn taken off, although in the former case the motion of the diaphragm is exactly the same.” This is an important point. The action of the horn is not somehow to make the diaphragm move more vigorously; rather, the diaphragm motion is the same. More power is produced because of the presence of an enclosing chamber and the horn that leads from it. The former resonantly loads the source; the latter gets the sound out with minimal reflections. — Eric J. Heller, Why You Hear What You Hear- An…, 539

Categorization

• XREF: Doctrine of the gramophone horn connecting directly to impedance-matching concepts in acoustics and loudspeaker design. — connects to: Passive devices and even walls can amplify sound without power; A horn’s main benefit is source loading, not directional aiming.; Concentrating sound into a smaller solid angle raises horn sensitivity (+7 more)
• corroborated: 2 independent passages support this claim — Eric J. Heller, Why You Hear What You Hear- An…, 539

Broader Connections

• Concentrating sound into a smaller solid angle raises horn sensitivity #expands (0.85)
• Horn bells boost lower frequencies where wall friction dominates resonance enhancement #expands (0.82)
• Horn confinement amplifies siren output via proximity resonance. #expands (0.80)
• Coherent summation of aligned horns lets off-axis points act on-axis #exemplifies (0.78)
• Constant-directivity horns are efficient but cannot cover frequencies below 500 Hz #qualifies (0.75)