Glottal closing generates most vocal-tract excitatory energy.

Evidence

Notice that the main excitation is due to the closing event of the glottis, since this contains most of the excitatory energy at the formant frequencies. Recognize also that the glottal function is a non-LTI (not linear and time-invariant) system since its parameters – for example, the acoustic impedance in the glottal orifice – vary with glottal closing and opening. Thus, Equation (5.1) is not valid in a strict sense. Since the interaction of the vocal tract and the vocal folds is relatively weak, such a simplified and linearized model is useful as a first approximation. — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 611

Categorization

• QUESTION: The glottis is formally non-LTI, yet ‘relatively weak’ interaction justifies linearity — how weak is weak enough, quantitatively?
• XREF: Perceptually motivated: abrupt glottal closure is what gives vowels their formant excitation — links to why voice quality (breathy vs pressed) changes acoustics.
• corroborated: 2 independent passages support this claim — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 611