The Mechanics of Speech Phonemes are created when the diaphragm forces air from the lungs into the trachea to produce sound. Most phonemes are voiced and involve the excitation of the vocal chords by periodic pulses of air created by the glottis. Other phonemes are unvoiced and result from the hissing created by steady airflow over surfaces in the mouth. Finally, some phonemes include both mechanisms. Humans varies the sizes of the oral and nasal cavities, teeth and lip apertures, and tongue position to control the resonant frequencies of the post-throat conditioning.
True phonemes are generally non-stationary.
The fundamental pitch and overtones vary with the movements of the vocal tract and facial muscles. Intensity varies with diaphragm pressure. Finally, the subconscious assimilation of auditory and tactile feedback by a speaking person is of demonstrated importance but is poorly understood.