ACOUSTIC COUPLING IN PHONATION AND ITS EFFECT ON ...

13with previous considerations on the role of the inertance and viscous losses [5,6,59],and relate the orifice discharge coefficient with a time-varying k t coefficient in equation(2.3). Similar discrepancies between the aerodynamics of the opening and closingportions have been observed [85]. The separation point of the glottal airflow and thevocal fold walls during the closing portion of the cycle was observed to occur afterthe minimum glottal area from Bernoulli’s equation. Further along these lines, it wassuggested that the Coanda effect, where the jet remains arbitrarily attached to one ofthe vocal folds walls, can occur during divergent configurations [86,87]. Despite theinability of the Bernoulli regime to properly describe the closing portion of the cycle,all of these recent studies support that its accuracy during the convergent portion isacceptable.2.1.3 Additional impedance considerationsTwo different core options are normally used to represent the origin of the sourcewhen expressing the complete system in term of lumped impedances: the use of anideal pressure or ideal flow source. Although these two are technically interchangeable,they are typically used for different purposes.Located at the alveolar level, an ideal pressure source tends to produce a moreintuitive idea of voice production. However, it fails to represent the dipole nature ofthe source at the glottis in a circuit analogy. Although some ad hoc measures havebeen proposed to represent a dipole source using a pressure source (cf. [13] page 92),these require the use of a pressure source at the glottis and no subglottal pressure,thus distorting its original intuitive nature.The use of an ideal flow source to represent the glottal excitation has also beenexplored in electrical analog models of voice production [3,13,47,88]. The traditionalapproach has been to start with a ideal pressure model and convert it into its Nortonequivalent, yet the equivalence is valid only for linear elements. Thus, the nonlinear