Infrasound under Control

Big vibrating machines like vibro-screens move the environmental air causing sound waves. As these machines have mostly a working frequency under 20 Hz, the sound waves cannot be heard by human ears. They may, however, cause annoyance or discomfort to exposed persons. These waves have the ability to propagate for long distances thus causing trouble in the neighbourhood like vibrating window sheets.

This phenomena, called infrasound, passes through walls of conventional housings due to its long wave and cannot be stopped by ear protectors as it influences other body organs like stomach and lungs.

This paper describes a housing technology, which succeeded in reducing the infrasound of a 20m² vibrating drum for more than 20 dB in a German foundry, rendering the environment acceptable for the workers and the neighbours.

It consists of several wall parts of reinforced concrete built together in such a way that parallelity is avoided. Thus the infrasound waves reflect in different directions and eliminate one another without causing resonance

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