When a singer has good vocal technique, his larynx should move (float) up and down depending on the sort of singing that he is performing. For instance, his larynx should lower somewhat for strong, lower register, low note, singing, and, by contrast, his larynx should rise to some extent if he is singing falsetto—and there are many variations in between with respect to the vertical movements of his larynx. 

Moreover, certain vowel sounds can influence the vertical movements of the larynx: the "OO" vowel (as in "boot"), for example, can cause a singer's larynx to drop to some degree, as compared to, for instance, the "EE" vowel (as in "beet"), which typically has the opposite result.