Stig Ingemansson’s Noise Control: Principles and Practice – A2 Sound Behavior: Causes of Production

Airborne sound is usually produced by vibration in solids and fluids

Principle:

When we use the word ‘sound’ in everyday speech we usually mean airborne sound.  Airborne sound is normally produced by vibrations in solid materials – structureborne sound – or pressure variations in fluids – fluidborne sound – which are coupled to a surface that radiates airborne sound.  For example, vibrations of the strings of a stringed instrument are transmitted through the bridge to the sound box.  When the sound box vibrates sound is transmitted to the surrounding air.  A circulating pump produces pressure variations in the water of a heating system.  The fluidborne vibrations are transmitted to the radiators whose large surface areas radiate airborne sound.

Example

The radiation of sound from a pipe with a small diameter is usually negligible.  However, a rigid connection of the pipe to an efficient radiator like a wall or ceiling may convert the pipe into a noise problem.

Control Measure

If flexible supports are substituted for rigid connections the pipe vibrations will not be transmitted.  This type of isolation is usually necessary for refrigeration and hydraulic lines.

More about this series

The illustrations in this article appeared first in a book published in Swedish by Arbetarskyddsfonden, the Swedish Work Environment Fund. The Fund was established by national legislation in Sweden to conduct research and education in the field of work environment improvement, and is jointly operated by Swedish employers and labor unions.

The book was translated into English and disseminated as a guide for workers and employers by the U.S. Department of Labor. It has also been translated into other languages, notably Finnish and Danish, but its overall circulation has been limited.  The illustrations are being republished here to give them wider circulation, particularly among noise control engineers.

The formulation of the principles, the choice of examples and the preparation of preliminary sketches was the work of Stig Ingemansson. The original illustrations were prepared by Claes Folkesson.

The principles are presented in eight sections:

A. Sound behavior (8)

B. Sound from vibrating plates (8)

C. Sound production in air or gases (7)

D. Sound production in flowing liquids (2)

E. Sound propagation indoors (5)

F. Sound propagation in ducts (6)

G. Sound from vibrating machines (6)

H. Sound reduction by enclosure walls (5)