The size control of velopharyngeal opening is an important variable for the acoustic profile characterization of hypernasal speech. To investigate frequency spectral aspects of F1, F2, F3, nasal formant (FN) and anti-formant, in Hertz, for vowels [a] and [ã] at different velopharyngeal openings produced in the bulb of a palatal prosthesis replica used by a patient with velopharyngeal insufficiency. Speech recordings were obtained for four words (pato/mato and panto/manto) produced within a carrier phrase in 5 conditions of velopharyngeal functioning: prosthesis with no openings (control condition: CC); prosthesis with bulb opening of 10 mm² (experimental condition with 10 mm² opening: EC10), prosthesis with a 20 mm² opening (EC20), prosthesis with a 30 mm² opening (EC30), and without the prosthesis (ECO). Five speech-language pathologists made a live rating of speech nasality during the reading of an oral passage. The recordings were used for spectral analysis. F1 values were significantly higher for [a] when compared to [ã] in all conditions. F2 values for [a] in EC20 and EC30 were significantly lower than values in the other conditions, being closer to the values presented for [ã]. F3 values were not significantly different between the testing conditions. There was a relationship between FN and anti-formants, and the auditory perception of nasality for conditions EC10 and EC20. Significant changes were observed in the studied spectral values according to changes in the velopharyngeal opening size.22515-20