The Larynx
The larynx or voice box is a cylindrical framework of cartilage that serves to anchor the vocal folds. When the muscles of the vocal folds contract, the airflow from the lungs is impeded until the vocal folds are forced apart again by the increasing air pressure from the lungs. This process continues in a periodic cycle that is felt as a vibration (buzzing). In singing, the vibration frequency of the vocal folds determines the pitch of the sound produced. Voiced phonemes such as the pure vowels are, by definition, distinguished by the buzzing sound of this periodic oscillation of the vocal cords.
The lips of the mouth can be used in a similar way to create a similar sound, as any toddler or trumpeter can demonstrate. A rubber balloon, inflated but not tied off and stretched tightly across the neck produces a squeak or buzz, depending on the tension across the neck and the level of pressure inside the balloon. Similar actions, with similar results, occur when the vocal cords are contracted or relaxed across the larynx.
Read more about this topic: Place Of Articulation