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How do louder and softer speech result from changes in airflow and movement?

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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.

Louder and softer speech are primarily determined by the intensity of vocal production, which is influenced by both the pressure of the airstream and the vigor of articulatory movements.

Vocal Intensity and Airflow

Vocal intensity depends largely on the amplitude of vocal cord vibrations, which is driven by the pressure of the subglottic airstream. Increased expiratory effort from the lungs results in greater vocal volume. Conversely, all articulatory movements—including the initial expulsion of air from the lungs—can be performed with varying degrees of vigor, directly resulting in louder or softer speech or increased loudness on specific parts of an utterance.12

Resonator Influence

Beyond airflow, the "projective potential" of the voice is affected by the shape of the vocal tract. A flexible, wide vocal tract acts like a horn, enhancing sound radiation. In contrast, a constricted or tightened throat can muffle the sound, reducing its carrying power. Configurations such as a widely opened mouth and a widened pharynx allow for the unimpeded radiation of vocal cord vibrations, producing a louder, brighter sound.1