Sound is the succession of pressure changes which are propagated in a compressible medium, such as air, water or solid materials. One also refers to this as “acoustic waves” instead of sound. Contrary to electromagnetic waves, acoustic waves are a mechanical phenomenon.
Acoustic waves are not always (clearly) audible. This is the case with infrasound and ultrasound. Acoustic vibrations with a frequency lower than 20 Hz are called infrasound. With a frequency higher than 20 kHz (=20,000 Hz) one refers to it as ultrasound. Sounds with a frequency between 20 Hz and 20,000 Hz are actually audible.
One refers to sound pollution when sound is perceived as unpleasant. The degree of nuisance depends on the level of the sound pressure and the properties such as sharpness and tonality. For example, a song is perceived as less unpleasant than a passing train. Also subjective factors (such as tiredness) can play a role with the negative appreciation of sound.
Sound pollution has become an important threat to the quality of life in densely populated and industrialized countries such as Belgium. The main causes of this nuisance are traffic, transport, industrial and some recreational activities.
The sound emission of noisy machines and appliances causes noise nuisance in our environment: outdoor equipment, household appliances, music installations, …. In this section you will find information on the effects of sound, infrasound and ultrasound, sound standards for noisy products and means of transport. Also the competences of the different authorities responsible for the limitation of sound nuisance are elucidated here.
While reading you may come across technical terms you are not familiar with. Then please refer to the page “Explanation of technical terms concerning sound”.