That which is perceived as ‘voice’ is merely a perception of moving air, and it is impossible to support either a column of air or the vibrations activated by the vocal folds which have caused that motion. Neither the abdominals nor the diaphragm create, control, or determine the quality of those vibratory patterns. The intrinsic muscles of the larynx, whose role during phonation is to maintain vocal fold tension proportional to the frequency of the vibrations (pitch) being sung, are unaffected by either abdominal or diaphragmatic activity (which is not to deny, however, that such activity should take place reflexively).
Both the abdominals and the diaphragm interact with the larynx, but the abdominals, which can be controlled independently, should hold firmly as a response to a correct technique of singing (i.e., the ability of the laryngeal musculature to coordinate effectively), and not considered a causative factor necessary to the development of vocal skills or something to be acted upon. Moreover, the diaphragm responds reflexively under all conditions and cannot be controlled directly – as is demonstrated when attempts are made to pacify its fluttering movement when under nervous tension.
Efforts made to support the voice and to steady it have neither a positive nor a negative effect on the adjustments made by the supra- and infrahyoids and their ability to stabilize the larynx, preventing it from rising too high or descending into too low a position.
Cornelius L. Reid 