There may be times when you will need to use your skills to construct an acoustic enclosure or screen, soundproof a room or fabricate acoustic ductwork. This document gives some tips on materials to use and how to avoid the common pitfalls.
What acoustic materials do?
The materials you use for noise reduction can work in four basic ways, such as:
- sound isolation - stopping sound from passing through, by reflecting it
- sound absorption - soaking up sound so it is not reflected
- vibration isolation - stopping vibration energy passing from one point to another
- vibration absorption - soaking up the vibration by damping.
Noise barrier
You can screen noise by building a noise barrier from a sound isolating material.
An additional sound absorbing layer stops sound echoing in the area near the source and bouncing over the barrier. It can be secured at its edges in metal channel sections or with timber studs and given a protective facing (see 'sound absorption' above).
Some ideas
- Make it a mobile screen by adding wheels.
- Add a glass or Perspex viewing window.
- Install sound absorbing material on the ceiling above and the wall behind which will work better.
Acoustic enclosures
An acoustic enclosure can range in size from a small box or cover to a tractor cab, up to a large machine enclosure or sound proofed room.
Points to watch
- The wall materials need to be heavy enough to isolate the required amount of sound (see 'sound isolation' above).
- Use an absorbing layer on the inside to reduce sound build-up.
- Seal off any gaps or openings by block-off pieces and gunned sealant, or flexible flaps where openings are necessary.
- Make sure any doors, hatches or removable panels have full seals on each contacting edge.
- Make sure the enclosure is not touching any vibrating part of the machine, or it may vibrate as well - isolate any pipework which penetrates the enclosure, sealing the gap with soft sealant.
- Don't forget that the machine may need ventilation - provide silenced airflow ductwork (see below).
Acoustic ductwork
Acoustic ducts can allow enough airflow while absorbing noise as it passes along the duct. Note also that noise travels along intake ducts against the airflow.
Points to watch
- The outer ductwork layer needs to be thick enough to prevent noise 'breakout'.
- The absorbing material needs to be thick enough to absorb sound over a wide range of frequencies, e.g., 50 mm thick fibreglass is a typical lining thickness.
- The duct cross-section needs to be large enough to allow air to flow with little restriction.
- The length of duct which is lined with absorbing material needs to be long enough to reduce sound sufficiently - the larger the duct size, the longer the lined length needs to be.
- You may need to insert a flexible 'vibration break' between the lined duct and the noise source (see below).
In summary
Trade skills can be used to reduce noise in the workplace. Having a basic knowledge of acoustic materials and how they work and knowing some of the pitfalls in 'building quiet' will help. For further assistance, you can contact the material suppliers or research architectural acoustics.