It is adjustable and has hard surfaces. Think of a tuning fork (the cords) vibrating and touching a plate (the larynx). Due to its direct contact, the plate is forced to vibrate with the tuning fork. The cords and larynx are similar to the tuning fork and plate, in that the cords are housed within the larynx. They are in direct contact, with the closest of proximities. When this happens, it is called forced resonance. The singer begins to have the true “singer’s ring” in the voice, which is indicative of much training.