The physical act of singing relies on a pair of small, specialized structures within the larynx known as the vocal folds, often informally called vocal cords. These twin infoldings of mucous membrane, ligament, and muscle are the primary source of sound, converting a steady stream of air into vibrations. While speaking requires vocal coordination, singing demands a significantly higher level of fine-tuned muscular control to achieve a wide range of frequencies, dynamic levels, and tonal colors. This interplay between breath and muscle allows a singer to transform simple airflow into a complex musical instrument.
The Basic Mechanism of Vocal Sound
The creation of vocal sound, a process called phonation, begins with the controlled release of air from the lungs. This air builds up pressure directly beneath the vocal folds in the windpipe, termed subglottic pressure. Before sound can be produced, the vocal folds must move together (adduction), closing the space between them known as the glottis. Once the folds are approximated, the rising subglottic pressure overcomes the muscular resistance, forcing the folds to burst open and release a puff of air. This rapid burst of airflow causes the pressure between the folds to drop sharply due to the Bernoulli effect. This drop in pressure, combined with the natural elastic recoil of the tissue, immediately pulls the vocal folds back toward one another to close the glottis. This entire cycle of opening and closing happens rapidly, repeating hundreds of times per second, which generates the initial buzzing sound perceived as the voice.
How Singers Control Pitch and Range
The frequency of vocal fold vibration determines the pitch of the note being sung. Singers manipulate this frequency by altering three properties of the vocal folds: length, tension, and mass. The primary muscles responsible for these adjustments are the intrinsic laryngeal muscles. To reach higher pitches, the cricothyroid (CT) muscle contracts, tilting the thyroid cartilage forward and stretching the vocal folds, making them longer and thinner. This increased tension causes the folds to vibrate at a faster rate, thus producing a higher frequency sound. Conversely, the thyroarytenoid (TA) muscle, which forms the body of the vocal fold, contracts to shorten and thicken the folds for lower notes. The TA muscle’s activity is dominant in the lower pitch range, where the vocal folds are robustly vibrating along their entire mass. As the singer ascends in pitch, the CT muscle becomes progressively more active, stretching the folds and thinning the vibrating edge. This muscular coordination allows the singer to transition smoothly between different vocal registers, such as chest voice and head voice, by continuously managing the relative activity between the TA and CT muscles.
Generating Volume and Projection
The loudness of the singing voice is primarily controlled by the amount of air pressure directed at the vocal folds. To increase volume, the singer must generate a higher subglottic pressure, which requires more focused breath support from the diaphragm and core musculature. This heightened pressure forces the vocal folds to separate more forcefully, resulting in a larger pulse of air released into the vocal tract. However, increasing air pressure must be balanced by sufficient vocal fold resistance. To manage the higher pressure and achieve a clear, loud tone, the vocal folds must increase their medial compression, or glottal closure, by adducting more firmly. This more complete closure ensures that the maximum amount of air pressure is momentarily contained and then converted into acoustic energy when the folds finally separate. The sound generated at the vocal folds is then amplified and shaped by the vocal tract, which includes the throat, mouth, and nasal cavities acting as resonators. Professional singers learn to manipulate the shape of the vocal tract to maximize the efficiency of sound radiation. This technique minimizes the need for excessive air pressure and vocal fold compression to achieve projection, reducing the risk of strain.
Maintaining Vocal Cord Health
The delicate tissues of the vocal folds require conscious care, especially when subjected to the intensity of singing. Hydration is the most important factor for vocal health, as the mucous membrane covering the folds requires a thin, slippery layer of lubrication for optimal vibration. Singers should aim to consume at least eight glasses of water daily. Internal hydration takes time to reach the vocal folds, so chronic dehydration cannot be quickly fixed right before a performance. Using a personal humidifier, particularly in dry environments or during sleep, helps to provide external moisture that directly benefits the vocal mechanism.
Avoiding substances like caffeine and alcohol is also recommended, as they can act as diuretics and reduce the necessary lubrication layer. Managing lifestyle factors is also crucial, particularly avoiding vocal misuse such as yelling, screaming, or speaking loudly over prolonged periods. Singers are susceptible to irritation from acid reflux, where stomach acid travels up to the throat and inflames the vocal folds. Dietary adjustments, such as limiting spicy foods, citrus, and eating close to bedtime, can help mitigate this common issue. If the voice feels hoarse or strained, taking short periods of silence, known as vocal naps, allows the muscles and tissues to recover from fatigue.