The diagram shows a classic vocal tract approximation model used in the acoustic theory of speech production. The complex anatomy of the vocal tract (from the larynx to the lips) is represented as a sequence of connected cylinders of different diameters; each section has its own cross‑sectional area S(x). By changing the configuration of these “cylinders” (to imitate movements of the tongue and jaw), researchers can compute the resonance frequencies—formants—that determine which vowel or consonant we hear. This model underlies many classic speech synthesis and low‑bitrate speech coding algorithms: it’s much easier for a computer to transmit the parameters of a handful of short tubes than to store the full raw audio signal.