Resonance, Formants and Larynx Position

The vocal tract is a tube closed at the folds and open at the lips. Such a tube resonates at odd multiples of a quarter wavelength, so a 17.5 cm male tract has resonances close to 500, 1500, 2500 and 3500 Hz. These are the formants; a real tract with its bulges and constrictions moves them around. F1 mainly follows the jaw opening (and tongue height), F2 follows the tongue's front–back position, and lip rounding lowers all of them. Lowering the larynx or protruding the lips lengthens the tube and lowers every formant; raising the larynx or spreading the lips shortens it and raises them.

When one note is sung, only its harmonics exist; formants don't make sound, they amplify the harmonics near them. As the pitch rises above the first formant, the singer's fundamental overtakes it and the vowel can lose clarity — which is why professional soprano singers tune F1 to the pitch (opening the mouth wider at high notes) and sacrifice vowel identity for volume. The male singer's task is different: he wants F3, F4 and F5 to cluster near 3 kHz. A narrow epilaryngeal tube above the folds, relative to the wider pharynx above it, produces this cluster: the singer's formant. It adds 10–20 dB of energy in a region where the orchestra is weaker and where the ear is very sensitive, so a voice can be heard over 80 players without being pushed.

A low, stable larynx lengthens the tract (lower formants, a darker and rounder tone), widens the pharynx and helps to keep the epilarynx narrow, so the singer's formant forms easily. A rising larynx has the opposite effect: shorter tube, higher formants, a narrower pharynx and a thin tone. Beyond acoustics, the larynx rises for mechanical reasons: the muscles above the hyoid pull on it whenever the tongue and jaw tense or whenever the singer 'reaches' for a note. A stable larynx means the muscles around it are balanced so that the cricothyroid is free to stretch the folds without a fight.

Style and common sense. In classical singing the larynx is usually stable and slightly lower than in speech; in pop and musical theatre it is often a bit higher but should still be stable, not climbing. Forcing the larynx down (an over-dark or 'swallowed' tone) is as problematic as letting it rise: it takes a muscular effort, narrows the throat and loses the ring. The cues that work without forcing are the start of a yawn, the sense of a long neck, the 'inner smile' and rounding the lips a little as you ascend; if you feel pressure, you have gone too far.