Special Session: “Acoustic and Physiological Aspects of Singing”

Organizer: Johan Sundberg

In cooperation of: Miriam Havel, Brian Gill, Jessica Lee, Filipa MB Lã, and Svante Granqvist.

Advantages and disadvantages of singing with a velopharyngeal (VP) opening has long been a theme of controversies between teachers of singing and between voice experts. Some argue that the VPO should be “patently closed” in vowel production, while others report voice improvements after instructing students to sing vowels with a narrow VP opening. I will present a family of studies, which I have had the privilege of carrying out with friends and colleagues from different fields, and which seem to shed light on effects of such an opening.

Together with Birch and associates (1) I examined the VP port in 17 professionally performing opera singers by means of a nasofiberscope.  For the vowels /u, a/, but rarely for the vowel /i/, we found VP openings of different sizes in many of these singers. A listening test revealed that a narrow VP port did not necessarily result in a nasalized vowel quality. In a follow-up study (2) we analyzed the effect of connecting a 10 cm long quasi-nasal-tube resonator to a 20 cm long-quasi-vocal tract tube. We found, as expected, that the resonance frequency of the shorter tube created a dip in the transfer function of the quasi-vocal tract tube. 

In an experiment with Gill and associates (3) we asked singers to sing a vowel sequence at different pitches with the VP port (i) closed, (ii) slightly open and (iii) wide open. We measured the audio signal and also the oral and nasal airflow signals as picked up by a Glottal Enterprises flow mask. The latter signals allowed us to verify that the singers managed to produce reliable examples of the three conditions. The audio signal was analyzed in terms of long-term-average spectra (LTAS). The results showed that, as an average across participants, a narrow VP opening enhanced the level of the 2 – 4 kHz range of the LTAS by about 5 dB relative to the overall LTAS level. In other words, a narrow VP opening tended to change the spectrum balance in favor of the spectrum partials in the frequency range of the singers’ formant cluster.

Recent experiments with Filipa MB Lã and Svante Granqvist (4) support the assumption that an open VP port can reduce the risk for voice breaks caused by source-filter interaction. Nine student choir singers sang glide tones on an intended neutral vowel while pressing against the mouth the end of a 70 cm long tube. They did this under three conditions: (i) with the far end of the tube open, (ii) with the far end of the tube open but while nasalizing the vowel and (iii) with a piece of cotton wool in the far end, thus attenuating the lowest resonances of the compound vocal tract&tube resonator. Under condition (i) a great number of voice breaks were observed, but the number of breaks was almost halved in (ii), when the participants nasalized the vowel. Likewise, it was almost halved under condition (iii) when a piece of cotton wool attenuated the lowest resonances. Thus, the risk of voice breaks was reduced when the lowest resonances were attenuated.

Together with Miriam Havel and associates I have experimentally measured effects of a VP opening on the sound transfer of the vocal tract. We used 3-D models of vocal tracts coupled to 3-D models of nasal tracts via coupling tubes of different sizes. Increasing the cross-sectional area of the coupling tubes left the high frequency range basically unaffected but systematically attenuated the low frequency range, like the piece of cotton wool did in the 70 cm long tube. This supports the assumption that a VP opening can reduce the risk for voice breaks caused by source-filter interaction. However, it also shows that it can increase the levels in the high frequency range, an effect that otherwise typically requires an increase of vocal effort.

Taken together, these studies suggest that a narrow VP opening, habitually used by many professional opera singers, can reduce the risk for voice breaks due to source-filter interaction and at the same time automatically enhance the singers’ formant cluster without requiring increase of vocal effort. 


  1. Birch P, Gümoes B, Stavad H, Prytz S, Björkner E, Sundberg J (2002) “Velum behavior in professional classic operatic singing”, J Voice 16, 61-71.
  2. Sundberg J, Birch P, Gümoes B, Stavad H, Prytz S, Karle A (2007) Experimental findings on the nasal tract resonator in singing, J Voice 21, 127-137.
  3. Gill BP, Lee J, MB Lã F, Sundberg J. Spectrum Effects of a Velopharyngeal Opening in Singing, Journal of Voice 34:3, 156-167
  4. Sundberg, MB Lã, Granqvist, forthcoming
  5. Havel M, Sundberg J, Traser L, Burdumy M, Echternach M. Effects of Nasalization on Vocal Tract Response Curve. J Voice early on the internet.