larynx is part of throat . It is responsible for production of sound. Larynx moves when we swallow something . Inside the larynx there are 2 vocal cords There are small gap between them .This gap allow air to pass through it. When we speak, air is forced into this small gap by the lungs. This prompt vocal cords to vibrate. Since vibrating object produce sound , sound is produce due to the vibration of vocal cords.