Silencers and industrial mufflers are used to limit noise emissions in applications like fan inlets and discharges, stacks, vents, equipment/process enclosure ventilations, power generators, etc…
They consist of ducts through which the air-flow is forced to pass, providing attenuation of the propagated noise generated either by the machine/equipment upstream the duct or by the flow itself (flow-noise).
Optimal muffler design requires maximization of noise absorption and minimization of flow pressure losses.
Noise attenuation is typically obtained through the following mechanisms:
- Reactive Mufflers
- Destructive interference of sound waves (e.g. resonant cavities).
- Waves back-reflection towards the source (e.g. expansion chambers providing sudden change in cross sectional area of the duct).
- Dissipative Mufflers
- Dissipation of acoustic energy into heat (e.g. damping material: foam, fibrous material, glass fiber; perforated sheets: metallic sheet punched (hole size of mm) supporting the damping material).