The production of sound requires some kind of energy and frequently this energy makes something vibrate. In the case ofhuman speech the thing vibrating is usually the vocal cords which are energised by air pressure from the lungs. Any such sound produced in the larynx is then modified by the resonating chambers of the pharynx, the mouth and, in some cases, the nasal cavities. The listener's impression of sound quality will be determined by the way in which the speaker's vibrator and resonators function together.