Phonetics Continued - Articulation and Description of English Vowels. Properties of Vowels. Most Sonorant (Audible) Sounds. Almost always voiced. Vowel sounds change according to the shape of the vocal tract, no obstructions in vowels. Four parameters of vowels - Tongue HEIGHT: high / mid / low. Tongue BACKNESS: front / central / back. Vowel Trapezium: front, central, back. Tongue Height exercise explanation.