# Acoustic and Aerodynamic Coupling during
## 1 Introduction
[20] compared the transfer functions of replicas with computational MRI-based VT models and found good agreement, as well. In recent years, the influence of anatomical details like the lips or the sinus piriformi have been analyzed with regard to their acoustical impact. Whereas the lips [21; 22], the piriform fossae and the vallecula [20] only showed negligible or little impact on the transfer function with deviations less than 5% below 4 kHz, the acoustic influence of the teeth depends on the vowel that is phonated and the mouth opening. In the study of [PERSON] et al., the effect of teeth on the VT transfer function was investigated. Although they found a significant effect of the teeth on the resulting resonance frequencies in several individual VTs, these frequencies changed by less than 150 cents (i.e., 1.5 semi-tones) for VT shapes that exhibit no side branches or side cavities. This is the case for high-pitched singing or vowels with a wide mouth opening like the vowel /a/. Another focus was set on the effect of the body position during phonation as MRI-imaging is commonly performed in supine position [23; 24]. The reports showed that the effect of the supine position is statistically insignificant for different registers of professional tenors, whereas 5 out of 10 untrained singers phonated statistically significantly different being unable to completely compensate the different direction of the gravitation force in the supine position. Hence, [PERSON] et al. [25] recommended to include only professional singers in research studies concerning VT acoustics. In this context, [PERSON] et al. [17] analyzed the VT shape during the register transition between modal and falsetto register sung by ten professional tenors, who performed the scale from C4 to A4 in the modal and the falsetto register. An overview of the different singing registers is given by [PERSON] [26]. The results show that the shape of the VT varies negligibly when the subject changes from the modal register to the falsetto register. However, if the subject remains in the modal register during the scale C4-A4, the shape changes significantly. This shows that for higher pitches the natural form of the VT is represented by the falsetto register. [PERSON] et al. [27] observed sudden jumps of the vocal fold oscillation frequency originating from an acoustic coupling between VT and vocal folds at oscillation frequencies near resonances of the VT. Similar results were reported by [PERSON] et al. [28] in a study with 18 subjects. They also found an acoustic coupling between the VT and the vocal folds, producing frequency jumps, subharmonic tones and chaotic vibration patterns of the vocal folds. Research of the VT impact on the glottal aerodynamics and structural dynamics is mainly focused on the immediate supraglottal region downstream of the vocal folds, especially on the ventricular folds impact [29; 30; 31; 32]. In this context, effects such as the reduction of the subglottal phonation threshold pressure [29], the decrease of laryngeal [30] and increase of glottal flow resistance [31; 32] and the stabilization of the acoustic output signal [29] were reported. A comprehensive study was presented by [PERSON] et al. [33], who performed qualitative flow visualization of the airflow in simplified, straightened VT models of the vowels /a/, /u/, and /i/ within a physical larynx model with self-oscillating vocal folds. They showed that for all observed vowels, large vortices appear in the supraglottal region, which disperse in the narrow pharyngeal part. The formant frequencies deviated from physiological values for the vowels /a/ and /i/, but showed good agreement for the vowel /u/. The results of previous studies indicate that experimental models of the VT allow a reproduction of the acoustic properties of the human VT. Furthermore, they reveal that a simplification of the VT as proposed by [PERSON] et al. [13] (straightened VT with circular cross section) has no significant effect on the formant frequencies below 5 kHz.