The human vocal tract behaves acoustically as a stopped pipe about 17.5 cm long.

Evidence

It is immediately clear that one cycle for the stopped pipe takes twice as long as one cycle for the open pipe if the pipe lengths are equal (ignoring a small end correction which has to be applied in practice). Its fundamental period is therefore double that for the open pipe, and its f0 is therefore half that for the open pipe, or an octave lower. This can be quantified by consid­ ering that the time taken to complete a complete cycle is the time required for the pulse to travel to the other end of the pipe and back twice, or four times the stopped pipe length (see Figure 4.15): where fundamental period of stopped pipe  th of the stopped pipe and velocity of sound c  The natural modes of a pipe are constrained as described in the “stand­ ing waves” section of Chapter 1. — David Howard, Jamie Angus, coustics and Psychoacoustics, 1198 (#expands, via linked claim)

Categorization

• XREF: connects to: The singer’s formant arises from a quarter-wave resonator in the larynx; The speech tract is modeled as a transmission line with pressure and volume-velocity variables; Vocal tract resonances measurably shape wind instrument timbre (+2 more)

Broader Connections

• A stopped pipe sounds an octave lower than an open pipe of equal length #expands (0.85) — David Howard, Jamie Angus, coustics and Psychoacoustics, 1198
• Vocal tract resonances measurably shape wind instrument timbre #expands (0.80)