To understand acoustic phenomena involved in the production of nasal vowels, we have built an experimental setting to obtain vocal tract transfer functions. The vocal tract is excited through the skin of the glottis by a white noise.
We have particulary studied the first nasal formant Fn1 situated around 250 Hz. It seems to agree with FENG'S predictions: Fn1 is a HELMHOLTZ resonance. But, because the wall vibration effects, the resonator can not be the simple nasopharyngeal tract. Namely the volume of this cavity should be greater than 800 cm3 ! Could an important role of the cranial cavity in the production of the nasal vowels and the nasal velar consonnant be then considered?
Bibliographic reference. Castelli, Eric / Perrier, Pascal / Badin, Pierre (1989): "Acoustic considerations upon the low nasal formant based on nasopharyngeal tract transfer function measurements", In EUROSPEECH-1989, 2412-2415.