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How does the amplitude of air-pressure pulses affect the loudness of a voiced sound?

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Uncover the science behind the transformation of sounds into speech — speech Speech is the faculty of producing articulated sounds, which, when blended together, form language.

The loudness of a voiced sound is largely determined by the amplitude of the air-pressure pulses produced by the vibrating vocal cords.1

When the vocal cords vibrate, they create regular pulses of air pressure that act as taps on the air within the vocal tract. Pulses with a larger amplitude result in a greater increase in air pressure, which is perceived by the listener as increased loudness.1

This relationship is rooted in the physics of sound, where the amplitude of a wave determines its intensity—the average rate of energy transmission—which the human ear interprets as loudness. In the context of speech, vocal intensity also depends on the pressure of the subglottic airstream; greater expiratory effort leads to higher amplitude vibrations and, consequently, greater vocal volume. Conversely, the efficiency with which these pulses are radiated depends on the shape and flexibility of the vocal tract, which acts as a resonator to enhance or muffle the sound.23