What is noise?
WHAT IS NOISE?
A rough guide to how noise is measured is shown below:-
30dB Quiet conversation
55dB Female speech
59dB Male speech
80dB Inside a sports car
90dB Road work machinery
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.
Soundproofing affects sound in two different ways: noise reduction and noise absorption. Noise reduction simply blocks the passage of sound waves through the use of distance and intervening objects in the sound path. Noise absorption operates by transforming the sound wave. Noise absorption involves suppressing echoes, reverberation, resonance and reflection. The damping characteristics of the materials it is made out of are important in noise absorption. The wetness or moisture level in a medium can also reflect sound waves, significantly reducing and distorting the sound traveling through it, making moisture an important factor insoundproofing.
Airborne noise – 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 – 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.
Soundproofing – 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 – 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
Sound barrier – 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 – 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.
Anti-vibration – 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.