The nasal tract as a resonator in singing.
Some experimental findings
Dept of Speech Music Hearing, KTH
SE-100 44 Stockholm
In an earlier investigation we measured nasal DC airflow and other signs of a velopharyngeal opening (VPO) in the production of the vowels /a, i, u/ as sung by 18 professional operatic singers of different classifications (Birch, Gümoes, Stavad, Prytz, Björkner, Sundberg 2002, J Voice 16, 61-71). Our results indicated that the vowel /a/ but not /u/ and /i/ quite commonly was sung with a VPO. In the present investigation the same group of researchers attempted to find out what benefit a VPO may have to offer singers. Two copies of a model of the vocal and nasal tracts, based on CAT scan data of a baritone singing the vowel /a/, were cast in epoxy. The models were divided into three blocks, one pharyngeal, one oral, and one nasal. In one of the models the pharyngeal tongue constriction and the VPO were eliminated. By inserting lumps of Plasticine into the model, approximations of the vocal tract shapes for /u/ or /i/ were obtained and combined with different VPOs. The transfer function was measured in terms of the response to a sine sweep from an earphone fastened to the glottal end.
The results revealed a highly resistive nasal tract. It was also found that a VPO considerably increased the bandwidth of the first formant for /i/ and /u/ but much less for /a/. On the other hand, a wide bandwidth typically produces a nasal quality, so this may be the reason why evidence for a VPO was rarely found in /u/ and /i/. The results further revealed that a VPO substantially decreased the level difference between the first and the third formant in all three vowels, such that it enhanced the singer's formant. As this would be a desirable effect, our results appear to explain why singers tend to sing the vowel /a/ with a VPO.
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