Experimental validation of flow models for a rigid vocal tract replica

Method for Fabricating Transparent Patient-Specific Vocal Tract Replicas

INTRODUCTION

Transparent, patient-specific vocal tract replicas are helpful in research and educational endeavors but challenging to procure. An accessible method for fabricating these models, improving on previously suggested processes, would make them more widely available.

METHOD

Detailed instructions for fabricating a transparent, patient-specific vocal tract model were addressed. The broad steps were (1) digitally reconstructing (patient-specific) vocal tract geometry, (2) producing a vocal tract mold (using methods such as three-dimensional [3D] printing), and (3) casting transparent material (such as silicone) around the vocal tract mold and removing the mold. The cavities remaining within the cast represented the exact geometry of the vocal tract.

DISCUSSION

A combination of 3D printing and silicone casting can produce useful vocal tract replicas. Several simple changes to previous methods can improve consistency and reduce the labor and cost of production. Limitations and potential modifications to expand the applications of this method are discussed.

Aeroacoustic analysis on individual characteristics in sibilant fricative production

The cause of individual acoustic characteristics of sibilant fricatives /s/ and /ʃ/ was analyzed by extracting vocal tract geometries and conducting aeroacoustic experiments and simulations on each geometry. The vocal tract geometries of five Japanese subjects while sustaining /s/ and /ʃ/ were collected by magnetic resonance imaging. Flow and sound generation in the vocal tracts was predicted by large eddy simulations of compressible flow. The characteristic dimensions of the vocal tracts were extracted and simplified vocal tract models were constructed to clarify the relationship between the geometries and the acoustic characteristics. The acoustic characteristics of sounds generated by the simplified models agreed well with the sounds predicted by the simulation, indicating that the proposed model is able to express the individual characteristics in the production of sibilant fricatives. A comparison of the models showed that the volume and length of a space downstream from the constriction are key factors controlling the acoustic characteristics of each subject.

Effects of tongue position in the simplified vocal tract model of Japanese sibilant fricatives /s/ and /ʃ/

The effects of tongue position on sound properties were investigated by using simplified models of sibilant fricatives /s/ and /ʃ/. These were constructed from medical images of a native Japanese-speaking subject who pronounced both fricative sounds. The sounds generated by the models were experimentally measured and compared with the subjects /s/ and /ʃ/. The position of tongue models altered the main peak frequency and spectral mean of the generated sound, which resulted in the reproduction of frequency characteristics of /s/ or /ʃ/ with the subjects tongue position.

The role of initial flow conditions for sibilant fricative production

Sibilant fricative sound production depends on the geometric and flow properties of the production system. Nevertheless, few studies deal with the potential impact of flow properties other than the inlet volume flow rate on the noise produced. In this work, an experimental study is presented using a replica based on a reconstructed oral cavity for the phoneme /s/. Initial flow conditions upstream from the sibilant groove are altered by varying the method of air supply. Statistical moments of the initial velocity distribution are characterized using hot-film anemometry and related to spectral features of the radiated acoustic pressure. Discrepancies in the dynamic amplitude (≤25%) and negative spectral slope (≤35%) observed at a constant Reynolds number but different initial upstream flow conditions are of the same order of magnitude as those previously reported in humans. This suggests that consideration of the upstream flow conditions is important in the study of sibilant fricative sound production.