Searching for the Causes of Chest-Falsetto Register Breaks under Anechoic Conditions

The origin of the breaks between chest and falsetto registers has remained one of the most controversial themes in voice science. The search for the causes of register breaks is reminiscent of a detective story. Classically, the breaks have been thought to be a consequence of a sudden change in laryngeal muscle activity causing a sudden change of vocal fold tension and frequency of oscillation. Experiments with excised human larynges showed, however, that sudden chest-falsetto breaks can spontaneously occur also when the vocal fold tension is changed smoothly (1). An alternative theoretical explanation of such phenomena emerged in the 1990s with the introduction of the theory of nonlinear dynamics to voice science. This theory showed that the phonatory system behaves like a nonlinear dynamic oscillator, where the chest and falsetto registers can be viewed as two possible ways of oscillation (attractors) that are inherent to the vocal apparatus (1). Voice breaks can then be recognized as “bifurcation events“ in which the oscillator suddenly changes the vibratory regime by shifting from one attractor to another. Whether the oscillation is in falsetto or chest register does not necessarily depend only on the laryngeal adjustment but also on other factors. Tiny changes in these factors (including, e.g., subglottal pressure, airflow, but also acoustic resonances in the breathing airways), can cause the oscillation to suddenly change from one register to another.