What vibrates in a tuba?

In a tuba, the vibrating element that produces sound is the large brass body of the instrument itself rather than a reed or string as in some other instruments. When an airflow with enough pressure from the player's breath, controlled by their embouchure (lip position and tension), goes into the mouthpiece, it sets the metal walls of the tuba resonating and generating the different pitch tones. The tuba's shape, its various tubing lengths and dimensions, and other design aspects enhance and determine the resulting notes and timbre unique to this brass instrument.