The tone of the actor's voice must be flexible and responsive to a high degree. The intention clearly must not be to reduce acting to the terms of vocal technique. The resonator of the voice consists of the three principal cavities above the larynx. These are the pharynx, the mouth, and the nose. Voices differ from each other in the same way. Two persons who possess identical AH vowel sounds could speak or sing them at the same pitch and with the same volume. The resonator may be expanded still further by means of rib-reserve breathing, which has the effect of drawing down the larynx from below, thus bringing about an increase in the size of the pharynx. In developing tone, therefore, two of our senses enter as controlling factors: touch and hearing. In developing nasal resonance, it is imperative to bear in mind the necessity for preserving a balance in tone between the main cavities and the nose itself.