There are two theories of how vowel sounds are made: 1 ... puffs of air from the vocal cords excite resonances in the head cavities (pharynx, mouth, nose, sinuses). To confirm one or the other ...

A polystyrene wig head and silicone ears with mic capsules ... listening studio To experiment it's easiest to start with binaural sound. You can capture spatial audio using simple in-ear mics.