ABSTRACT
Essentially all of these processes are capable of producing fluctuating forces which can set machine components into vibration, thus causing them to radiate noise directly or indirectly. In case f), aerodynamic flow variations can themselves radiate noise without necessarily setting mechanical components in motion. Frequently the source itself is
insignificant as a noise producer in its own right but, because of its effects on other components which are effective radiators of sound, a great deal of noise is produced. A common example of this is an alarm clock that when held in the hand is quite quiet but has an intolerable tick when standing on a bedside table. Similarly, while the level of vibration produced by a precision gearbox is low, poor mounting of the machine structure often results in substantial structure-radiated noise.
