Awareness of the acoustic registration events caused by changing interactions between the lower harmonics of the voice source and the first formant of the vocal tract can assist both teacher and student in working out a smooth, comfortable transition through the passaggio into the upper range of the male voice. This paper explains how knowledge and anticipation of these events, and of the passive vowel modifications that accompany them, can form the basis for effective pedagogic strategies. A relatively stable tube (vocal tract) length is necessary for timbral consistency and balance across the fundamental frequency range, since this can stabilize the general location of all formants and especially the singer’s formant cluster. However, upon ascending the scale, untrained males instinctively tend to activate muscles that shorten the tube in order to preserve the strong first formant/second harmonic (F1/H2) acoustic coupling of open timbre, resulting in “yell” timbre. If tube length and shape are kept stable during pitch ascent, the yell can be avoided by allowing the second harmonic to pass through and above the first formant. This results in the timbral shift referred to as covering or “turning over,” a shift which enables avoidance of the laryngeal muscular adjustments associated with pressed phonation. The variety of first formant locations, vowel by vowel, where these shifts occur creates opportunities for developing effective strategies for training the male passaggio.