Falsetto - Physiological Process

Physiological Process

The modal voice, or modal register, and falsetto register differ primarily in the action of the vocal cords. Production of the normal voice involves vibration of the entire vocal folds, with the glottis opening first at the bottom and then at the top. Production of falsetto, on the other hand, vibrates only the ligamentous edges of the vocal folds while leaving each fold's body relatively relaxed. Transition from modal voice to falsetto occurs when each vocal cord's main body, or vocalis muscle, relaxes, enabling the cricothyroid muscles to stretch the vocal ligaments. William Vennard describes this process as follows:

With the vocalis muscles relaxed it is possible for the cricothyroids to place great longitudinal tension upon the vocal ligaments. The tension can be increased in order to raise the pitch even after the maximum length of the cords has been reached. This makes the vocal folds thin so that there is negligible vertical phase difference. The vocalis muscles fall to the sides of the larynx and the vibration take place almost entirely in the ligaments.

In the modal register, the vocal folds (when viewed with a stroboscope) are seen to contact with each other completely during each vibration, closing the gap between them fully, if just for a very short time. This closure cuts off the escaping air. When the air pressure in the trachea rises as a result of this closure, the folds are blown apart, while the vocal processes of the arytenoid cartilages remain in apposition. This creates an oval-shaped gap between the folds and some air escapes, lowering the pressure inside the trachea. Rhythmic repetition of this movement, a certain number of times a second, creates a pitched note.

In falsetto, however, the vocal folds are seen to be blown apart and in untrained falsetto singers a permanent oval orifice is left in the middle between the edges of the two folds through which a certain volume of air escapes continuously as long as the register is engaged (the singer is singing using the voice). In skilled countertenors, however, the mucous membrane of the vocal folds contact with each other completely during each vibration cycle. The arytenoid cartilages are held in firm apposition in this voice register also. The length or size of the oval orifice or separation between the folds can vary, but it is known to get bigger in size as the pressure of air pushed out is increased.

The folds are made up of elastic and fatty tissue. The folds are covered on the surface by laryngeal mucous membrane which is supported deeper down underneath by the innermost fibres of the thyroarytenoid muscle. In falsetto the extreme membranous edges, i.e. the edges furthest away from the middle of the gap between the folds, appear to be the only parts vibrating. The mass corresponding to the innermost part of the thyro-arytenoid muscle remains still and motionless.

Some singers feel a sense of muscular relief when they change from the modal register to the falsetto register.

Research has revealed that not all speakers and singers produce falsetto in exactly the same way. Some speakers and singers leave the cartilaginous portion of the glottis open (sometimes called 'mutational chink'), and only the front two-thirds of the vocal ligaments enter the vibration. The resulting sound, which is typical of many adolescents, may be pure and flutelike, but is usually soft and anemic in quality. In others, the full length of the glottis opens and closes in each cycle. In still others, a phenomenon known as damping appears, with the amount of glottal opening becoming less and less as the pitch rises, until only a tiny slit appears on the highest pitches. The mutational chink type of falsetto is considered inefficient and weak, but there is little information available about the relative strengths and weaknesses of the other two types.