Can vocal economy in phonation be increased with an artificially lengthened vocal tract? A computer modeling study.

Voiced obstruents and phonation into tubes are widely used as vocal exercises. They increase the inertive reactance of the vocal tract in the 200-1000 Hz range and thereby reinforce vocal fold vibration. But the effect is strong only when the epilarynx tube is also narrowed. The present study focused on the effects of a 'resonance tube' (27 cm in length, 0.5 cm2 cross-sectional area, hard walls) on vocal tract reactance and the accompanying economy of voice production (defined as maximum flow declination rate (MFDR), divided by maximum area declination rate (MADR)). The vowel /u/ and phonation into the tube were simulated with a computer model. Three values were given to the cross-sectional area of the epilarynx tube (0.2 cm2, 0.5 cm2, and 1.6 cm2), which is at the opposite end of the vocal tract from the artificial 'resonance tube'. The degree of glottal adduction was varied in order to find the economy maximum for each epilarynx tube setting. Results showed that the 'resonance tube' lowered F1 from 300 Hz to 150 Hz and doubled the vocal tract inertive reactance at F0=100 Hz. The largest economy with the 'resonance tube' was obtained when the epilarynx tube was narrowed (relative to the rest of the vocal tract) and sufficiently tight adduction was used. Most importantly, the intraoral acoustic pressure (calculated at 0.8 cm behind the lips) was tripled with the tube. The results suggest that by optimizing the vibratory sensations in the face that are attributed to increased intraoral acoustic pressure, phonation into a tube may assist a trainee in finding an optimal glottal and epilaryngeal setting for the greatest vocal economy.