The role of the sinus cavities in the production of nasal vowels

The acoustic wave propagation inside the vocal tract was simulated assuming plane waves. When an acoustic tube having appropriate area function but no side branching cavities was used as the nasal tract, the low frequency nasal formant below the first formant of low vowels as observed in natural speech could not be simulated. The relatively short nasal tract with both ends open cannot produce the low nasal formant. We therefore employed a side cavity for the nasal tract system, which gave rise to the nasal formant in the expected frequency region. The computed output signals for different nasalized vowels sounded very naturally nasal.