These are styles, not physiological phenomena. There may be common tendencies in the technical approaches to some songs in some styles, but there are not hard and fast rules. An attempt to try to describe belt as “constricted” reflects a misunderstanding of what an ideal performance of a belt song would sound like. Judy Garland and Ethel Merman and Kate Smith had open throats and clear diction and options available to them that screamers do not have.
Why do I say this? Because the Mid-Atlantic region of the National Association of Teachers of Singing, published the passage below as guidance in helping teachers choose rep for their students to sing in the Musical Theatre division of the NATS Student auditions:
Scientific Characteristics of each style:
OPERA: Moderate subglottic pressure and glottal adduction, moderate jaw opening, lowered larynx, peak glottal permittance, short closed phase, good visibility of folds, strong fundamental, strong singer’s formant.
MIXED: Moderate subglottal pressure, moderate glottal adduction, wider jaw opening, slightly raised larynx, second formant highest (but first was present,) side walls of pharynx slightly advanced, folds less visible, singer’s formant present.
BELT: 10 decibels louder, high subglottic pressure, high glottal adduction, widest jaw opening, raised larynx, side walls very advanced, sinus piriform small, no fundamental, long closed phase, folds almost hidden, low singer’s formant.
OPERA: Moderate breath pressure and folds touching loosely, mouth open small amount, throat relaxed and open, larynx low, “ring” in sound.
MIXED: Moderate breath pressure, folds pressed together some, mouth moderately open, throat slightly constricted, larynx slightly raised, “ring” present but less than in opera.
BELT: High breath pressure and volume, folds pressed tightly together, mouth wide open, larynx raised, throat very constricted, no amplification of pitch being sung,
If belt numbers were always performed with the “scientific characteristics” attributed to the “belt” section above, I would hate them all. But this is not how good singers in any genre sing! This description of “belt” blurs the distinction between technique and style, and comes off as condescending to those who sing “nonlegit” rep.
I do not think it is wrong for NATS to change the rules to try to level the playing field a bit and require one legit and one nonlegit song for all the MT audtionees, but if they are expecting students to sing the “belt” numbers with a “very constricted” technique, why bother making this change? I am in discussion with some NATS folks and hope to get clarification on this. It seems that the problem is that they are afraid to use the terms legit and nonlegit or belt in the category descriptions and have painted themselves into an embarrassing corner with the “scientific” descriptions of the differences.