The Oral Cavity it the major Modulator of the three resonating cavities.
When consonants other than ãm, n and ngä are nasalized, they become unintelligible. This is because the air pressure needed to make a consonant escapes through the nose.
The Oral Cavity is the most amazing of all resonators. It is a modulator in that it can easily change in many ways the nature of the overtones generated by the larynx.
Using the articulators (particularly the jaw and the tongue) the size of the air masses in the oral cavity can be easily and quickly modified.
This is one major advantage of oral speech over Sign Language. The latter requires considerable effort (relatively speaking). My class on campus, which is three hours long, requires at least two Sign Language Interpreters. One only for the whole three hours would be a good candidate for Carpal Tunnel Syndrome.