Vocal pitch or fundamental frequency (F0) during speech and song has often been described by the mass of the vocal cords (vocal folds. However, mass (thicker and longer vocal folds) is an anatomical, not a functional concept. Why should this concept, that has been used so often, no longer have credence? The vocal fold is made up of a small amount of tissue that is attached to cartilages on three of its six sides. As a unit, the attached tissue has little freedom to move. Constraining the unattached tissue with boundaries creates vibrational displacements that are not uniform. Thus, the amount of material in vibration is hard to quantify and to associate with a single mass, as often attempted in the scientific and medical literature. It is better to consider two other variables that affect F0 control: length and stress of a laminated (layered) “string”. The formula for a vibrating string is used to prove this point where each layer should be considered a separate string.
Most would assume that if the thickness of the vibrating tissue is increased, and mass along with it, that F0 would be lowered. This is an incorrect assumption. If there is a new mass then there will be a tissue to work to restore the moving mass, or a new spring. Even if the mass increases an incredible amount one must consider the added stiffness to the vocal fold mass. What if the vocal fold was longer? This would result in a lower F0, but this would occur despite the length or thickness of the string. Hence, this would rule out mass as a variable. The idea that mass or thickness of the vocal folds effects F0 needs to be abandoned. Although the focal fold dimensions affect F0, the affects are explained only by elastic wave theory.
This new concept may change the way scientists study how the voice is created as well as give additional insights to surgeons when repairing damage vocal tissue or performing reconstructive surgery.
The above concept are discussed in more detail in a recently published article:
Ingo R. Titze. Vocal Fold Mass Is Not A Useful Quantity For Describing F0 In Vocalization. Journal of Speech, Language, and Hearing Research 2011 April; 54 (2):520-2.