Vocal Resonation - Sympathetic and Conductive Resonance

Sympathetic and Conductive Resonance

In a technical sense resonance is a relationship that exists between two bodies vibrating at the same frequency or a multiple thereof. In other words, the vibrations emanating from one body cause the other body to start vibrating in tune with it. A resonator may be defined as a secondary vibrator which is set into motion by the main vibrator and which adds its own characteristics to the generated sound waves.

There are two basic kinds of resonance: sympathetic resonance (or free resonance) and conductive resonance (or forced resonance) The essential difference between both types is what causes the resonator to start vibrating. In sympathetic resonance there is no physical contact between the two bodies. The resonator starts functioning because it receives vibrations through the air and responds to them sympathetically. In conductive resonance the resonator starts vibrating because it is in physical contact with a vibrating body.

Both types of resonance are at work in the human voice during speaking and singing. Much of the vibration felt by singers while singing is a result of conductive resonance. The vibrations created by the vocal folds travel along the bones, cartilages, and muscles of the neck, head, and upper chest, causing them to vibrate. There is little evidence that these vibratory sensations make any significant contribution to the external sound.

These same conductive vibrations, however, are good sensation guides for the singer, regardless of their effect on the external sound. These sensations provide evidence to the singer that his vocal folds are forming strong primary vibrations which are being carried from them to the head and chest. Thus these vibratory sensations can supply sensory feedback about the efficiency of the phonatory process to the singer.

In contrast, the sound a person hears listening to a singer is a product of sympathetic resonance. Vibrations created by the vocal cords travel through air from the larynx into the cavities of the throat and head, setting them into vibration. This is sympathetic resonance, without physical contact between these cavities and the vocal cords. The vocal resonator is not a sounding board, comparable with stringed instruments, but rather a column of air, with a shape that is not only complex, but highly variable. Vennard says:

Thus it may vibrate as a whole or in any of its parts. It should not be too hard to think of it as vibrating several ways at once. Indeed most vibrators do this, otherwise we would not have timbre, which consists of several frequencies of different intensities sounding together. Air is fully as capable of this as any other medium; indeed, the sounds of many diverse instruments are carried to the ear by the same air, are funnelled into the same tiny channel, and can still be heard as one sound or as sounds from the individual sources, depending upon the manner in which we give attention.