What is Noise?

Sound is a variation in the pressure of the air of a type which has an effect on our ears and brain. These pressure variations transfer energy from a source of vibration that can be naturally-occurring, such as by the wind or produced by humans such as by speech. Sound in the air can be caused by a variety of vibrations, such as the following.

• Moving objects: examples include loudspeakers, guitar strings, vibrating walls and human vocal chords.
• Moving air: examples include horns, organ pipes, mechanical fans and jet engines.

Noise is unwanted sound. The results of national surveys of typical exposure to noise show that over 50 per cent of the population are exposed to day-time noise levels that exceed the World Health Organisation (WHO) ratings for significant community annoyance. Other surveys report that around 50 per cent of people find their home in some way unsatisfactory because of noise intrusion. These results include people living in new homes built to modern building codes which require certain standards of noise control.

A satisfactory environment of sound quality therefore needs to be a major consideration when we create our built environment. This website deals with the technical and practical aspects of noise measurement and sound insulation. It will help you to:

• appreciate the environmental factors that affect human tolerance of noise
• understand the technical aspects of measuring and assessing noise
• be familiar with the common indices of noise assessment
• know the principles of noise control and their practical applications
• appreciate how sound is transmitted within buildings
• understand the difference between airborne sound and impact sound
• know the principles of sound absorption and sound insulation
• appreciate how typical walls and floors and other building elements perform in providing sound insulation
• be familiar with the common measurements of sound insulation
• understand the typical requirements for sound insulation of building regulations and codes.

The environmental and social definitions of noise take account of the effect of the sound rather than its technical nature. So even if a sound consists of the finest music it can be considered as noise if it occurs in the middle of the night! The following are some of the detrimental effects that noise can have on people and their environment:

• Hearing loss: excessive exposure to noise causes loss of hearing, as discussed in the previous chapter.
• Quality of life: noisy environments, such as areas near busy roads or airports, are considered unpleasant and undesirable.
• Interference: interference with significant sounds such as speech or music can be annoying and, in some situations, dangerous.
• Distraction: distraction from a particular task can cause inefficiency and inattention, which could be dangerous.
• Expense: the measures needed to control excessive noise are expensive. Businesses may also suffer loss of revenue in a noisy environment.