Example of Sound Sources

Vibrating bodies: drumhead, piano soundboard, ... Changing airflow:

• vibrating vocal folds open and close changing rate of airflow from lungs to vocal tract;
• holes in a rotating siren alternately periodically stop the flow of air;

Time-dependent heat sources:

• electrical spark producing a crackle;
• explosion producing a bang due to rapid heating causing air to expand;
• thunder results from rapid heating of air by a bolt of lighting.

Supersonic flow: shock waves result when air flows faster than the speed of sound:

• supersonic airplane,
• speeding rifle bullet,
• shock waves have been also known to occur in brass instruments (trumpet).