Why can a small loudspeaker seem to produce a low fundamental pitch that it cannot directly play?

A small loudspeaker can seem to produce a low fundamental pitch that it cannot physically reproduce due to a psychoacoustic phenomenon known as the missing fundamental, subjective fundamental, or periodicity pitch.1

The human ear functions as a spectrum analyzer that is highly responsive to the periodicity of complex sound waves. When a loudspeaker plays a series of higher-frequency harmonics, the ear detects the underlying periodicity of the wave and perceives the fundamental frequency—even if that specific frequency component is absent from the actual sound output.1

While the resulting sound will have a different timbre than it would if the fundamental were physically present, the brain interprets the harmonic structure to identify the fundamental pitch. This effect is a result of how the inner ear and auditory system process complex acoustic information, allowing listeners to perceive low-frequency tones despite the physical limitations of the speaker hardware.1