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Objectives: Nasality is one of the important parameters in pathology of voice resonance. Voice of normal adults has nasality to some extent. It appears that nasality, like other parameters of voice, can be affected by loudness which can be measured in experimental evaluations. This study was conducted to determine the effect of vocal loudness on nasalance of vowels in normal adults and to identify the relationship between these two factors in 18-28 year-old normal Persian-speaking adults.

Methods: In this descriptive-analytic and cross sectional study, sample voices of sixty-five randomly selected male and female 18 to 28 year-old normal Persian-speaking students of Rehabilitation Faculty in Tehran University of Medical sciences were studied. Mean of Nasalance in Persian vowels was computed with Nasal View software. The findings were analyzed with descriptive statistical analysis and one-way ANOVA.

Results: Maximum nasalance was in low voice and minimum nasalance was in loud voice in both men and women subjects. The statistical results show that nasalance in 3 levels of low, normal and loud voices have significant differences (P<0.05).

Discussion: In normal adults, vowel nasalance is decreased with increase in vocal loudness. This is an aspect of normal speech mechanism. The findings can be explained considering function of velopharengeal port, raise in subglottal air pressure in loud voice, and increased muscle contraction of pharynx and palate.