Relationship Between Subglottal Pressure and Sound Pressure Level in Untrained Voices

Subglottal pressure (P(s)) is strongly correlated with sound pressure level (SPL) and is easy to measure by means of commonly available equipment. The SPL/Ps ratio is strongly dependent on the efficiency of the phonatory apparatus and should be of great relevance to clinical practice. However, published normative data are still missing.

The subjects produced sequences of the syllable [pæ], and P(s) was measured as the oral pressure during the [p] occlusion. The P(s) to SPL relationship was determined at four pitches produced by 16 female and 15 male healthy voices and analyzed by means of regression analysis. Average correlation between P(s) and SPL, average SPL produced with a P(s) of 10 cm H(2)O, and average SPL increase produced by a doubling of P(s) were calculated for the female and for the male subjects. The significance of sex and pitch conditions was analyzed by means of analysis of variance (ANOVA).

Pitch was found to be an insignificant condition. The average correlation between P(s) and SPL was 0.83 and did not differ significantly between the female and male subjects. In female and male subjects, P(s) = 10 cm H(2)O produced 78.1 dB and 80.0 dB SPL at 0.3 m, and a doubling of P(s) generated 11.1 dB and 9.3 dB increase of SPL. Both these gender differences were statistically significant.

The relationship between Ps and SPL can be reliably established from series of repetitions of the syllable [pæ] produced with a continuously changing degree of vocal loudness. Male subjects produce slightly higher SPL for a given pressure than female subjects but gain less for a doubling of P(s). As these relationships appear to be affected by phonation type, it seems possible that in the future, the method can be used for documenting degree of phonatory hypofunction and hyperfunction.