What is Noise?
description of different types of noise
Noise is a form of pollution that affects us all but is unlike other forms of pollution. Once the noise stops, the pollution immediately comes to an end and the environment is free of it. Other forms ofpollutant such as sewerage and chemicals can be difficult to remove such as from water, soil and air.
The perception of noise is always a difficult subject. For some, the sound of a Grand Prix race is thrilling and gives enjoyment to many whereas; to others it is annoying and constitutes a noise nuisance. The same is typical of loud music. Many younger people among us enjoy listening to music set at high volumes when it infuriates others. So noise is subjective, in some ways it is enjoyed by some but for others, is an unwelcome form of noise pollution such as listening to your neighbour’s television when you are trying to quietly read a book.
It is now well known that excessive noise is a danger to health and can cause stress, sleeplessness, annoyance and many other uncomfortable symptoms.
A rough guide to how noise is measured is shown in the table below.
0dB Barely audible
30dB Quiet conversation
55dB Female speech
59dB Male speech
80dB Inside a sports car
90dB Road drill at 3 metres
100dB Noisy factory
140dB Threshold of pain
As you can see from the table, anything over 80dB in volume is very uncomfortable and can impair hearing. Lower volumes of noise can also be annoying if it is disturbing, particularly at night. Normally there are two ways to reduce noise nuisance. One is to eliminate the noise at source, giving instant relief or if this is not possible, introduce soundproofing to reduce the noise nuisance.
Sound travels as spherical ripples through the air much like the ripples created on a pond after a stone has been thrown in. As the ripples travel further away from their source, they reduce in intensity and if they hit a solid barrier or hit reeds, their energy is split up and dissipated in much the same way as sound absorbing materials work.
There are several different types of noise which are described as follows:
This is noise that is as the title suggests, airborne and is the type of noise created by speech and radio. Airborne noise tends to be the most annoying when noise is proving to be a nuisance.
Impact noise again is as the title suggests and is generated by items coming together such as a door slamming or footsteps over a hard floor. Installation of hard floors in flats is a widespread reason for noise nuisance to neighbours living below flats that have this type of floor installed.
Flanking noise is more often perceived in flats where noise is transmitted through the fabric of the building. Flanking noise is more often caused by impact noise and often travels through the walls of the building.
This is more of a problem if the walls are of a lightweight construction so it is important the correct density blocks are used in the construction of new flats today. Normally a minimum 7 kilonewton density block is specified today to reduce flanking noise nuisance and also help comply with the current regulations for noise control in flats and other multi-occupied buildings. Read more about flanking noise here
This is a term used when a reduction in the level of noise being heard is being reduced. It is often thought that if something has been soundproofed then the noise being generated has been silenced. This may be the case in some instances but is not always possible so a soundproofed situation may also refer to a noise nuisance that has been reduced in intensity as much as feasible or possible.
Sound absorption is normally required in enclosed spaces such as studios, halls and recreation centres to reduce reverberation (echo) of noise. An uninsulated hall is often unusable for many events due to excess reverberation. This makes speech difficult to comprehend and becomes more of a problem when people are speaking further apart.
A sound barrier is another way of describing a sound blocker and normally comprises insulation with a high mass which then reduces the amount of noise that can pass through it. A simple door can be described as a noise barrier when it is closed to reduce the sound of noisy kids playing just outside. Sound waves flow like water and air so it is impossible to use a sound barrier such as a fence or screen to stop noise but they are effective when used to reduce noise immediately on the other side of them. From distances farther away the noise reduction will be less efficient.
If you imagine a large stone in the middle of a river, you will see that the water flows quickly around it but leaves a slack area immediately behind the stone. Sound waves act in exactly the same way when presented with a sound barrier that is not complete.
Sound damping is normally required to reduce noise from resonating panels. Noise from resonating panels is annoying and addressed by stiffening the panels usually with a vibration damping pad that is glued on.
Noise from vibration is often a problem and can be caused by something simple such as a washing machine or a more extreme example such as heavy industrial machinery in a factory. Noise from vibration will generate both flanking noise and airborne noise depending on its location.
Written by Stephen Young - © Sound Service (Oxford) Ltd. 2003