Noise control is an active or passive means of reducing sound emissions, often incentivised by personal comfort, environmental considerations or legal compliance.
Practical and efficient noise control is wholly reliant on an accurate diagnosis of what is causing the noise, which often involves some degree of ‘detective work’.
The priority must always be to reduce the noise at source by engineering means once the main noise source has been verified.
The most common noise sources can be divided into Aerodynamic (fans, pneumatics, combustion) and Mechanical (impacts, friction):
Effective noise control would focus at reducing the noise from these sources as near the source at possible.
For example, where an impact is causing the noise:
1. can the impact be avoided?
2. if not, can the force of the impact be reduced?
3. and/or can the impact be cushioned?
4. and/or can the vibration generated by the impact be prevented from reaching the radiating surfaces?
Noise control for aerodynamic sources include Quiet Air Nozzles, Pneumatic Silencers and Quiet Fan Technology
There are four basic principles of noise control:
Sound insulation : prevent the transmission of noise by the introduction of a mass barrier. Common materials have high-density properties such as brick, concrete, metal etc.
Sound absorption : a porous material which acts as a ‘noise sponge’ by converting the sound energy into heat within the material. Common sound absorption materials include open cell foams and fibreglass
Vibration damping : applicable for large vibrating surfaces. The damping mechanism works by extracting the vibration energy from the thin sheet and dissipating it as heat. A common material is Sound Deadened Steel (SDS).
Vibration isolation : prevents transmission of vibration energy from a source to a receiver by introducing a flexible element or a physical break. Common vibration isolators are springs, rubber mounts, cork etc.
In architectural acoustics and environmental acoustics, noise control refers to the set of practises employed for noise mitigation. Within architectural acoustics these practises include: interior sound reverberation reduction, inter-room noise transfer mitigation and exterior building skin augmentation. More specific architectural noise control methods include the installation of acoustical gypsum, ceiling tiles, ceiling panels, carpet and draperies. In the field of environmental sound, common noise control practises include: design of noise barriers, development and enforcement of noise abatement legal codes and urban design.