Impedance mismatch at the pharynx junction shapes spectra via early return echoes

Evidence

The 3-cm-long tube, part of the pharynx just above the vocal folds, is constricted to be substantially narrower than the larynx lying just above (see Figure 17.9). The impedance mismatch at the junction sends an early return echo (or several echoes of decreasing amplitude that make the round-trip in the tube) with the now familiar consequence that broad features of the spectrum are shaped indelibly by this early sequence, according to the sculpting principle. — Eric J. Heller, Why You Hear What You Hear- An…, 1689