Tools & Resources
Acoustic Planning Can Beat Noise Headaches
Peace and quiet is a precious commodity in our industrialised, mechanised society. Acoustic engineering can offer economical solutions for most noise problems, and the key is to plan early and keep an open mind about design and materials.
When planning a new industrial installation, no matter what the size or type, addressing noise issues early in the planning process is the secret. Not only will it save money, but it can also have valuable "good neighbour" benefits. Industry inevitably creates noise and it will always be an issue to someone. Good acoustic planning can be so effective that many people can't believe their ears.
Case in point: when a large industrial plant was built some years ago in outer suburban Sydney, residents fought long and hard because of expected noise problems. And yet, several months into the plant's productive life, some nearby residents remained unaware that it had begun operating. Careful and innovative design stopped a problem before it began.
In short, it can be done. It's a matter of getting in early, doing the job properly and saving money.
Welcome Surprises
Whenever industry is planned anywhere near residential areas, there will be a need for noise abatement. So start before the project is even on paper, and keep an open mind about how solutions might best be achieved. The solutions available can often be surprisingly simple and inexpensive if those involved have the required expertise.
Different industries confront different noise problems in the nature and volume of noise and the times when it occurs. In addition to obvious industrial noises, such as hammering, grinding metal, the roar of furnaces and the vibration of heavy equipment, there are more subtle sounds. Consider the whirr of ventilation fans, the hiss of steam or the whine of motors, even the blare of a public address system.
Solutions are many and varied. They may be as simple as moving a door or re-orienting a building while it is still on paper.
The right choice of building materials can also be important, and here the options are much wider than many people realise. A steel composite panel, for example, can do the job of a thick, heavy concrete or masonry panel, if it is appropriately designed. It pays to be open-minded about materials.
Location and design of truck access routes is a classic case of how a little forethought can produce excellent results. In many factories these routes may be governed by relatively arbitrary site layout decisions. There is usually the potential to move them. At the simplest level, truck routes can often be kept away from nearby residences and noise-sensitive neighbours.
Where these simple measures are not enough, the additional measures required may still be relatively simple and economical. One such measure which has been used to very good effect involves the installation of curved acoustic "tunnels" outside vehicle access points to a large enclosed yard. The layout ensured that vehicle manoeuvring would be simple and safe, while the tunnels were positioned and lined to reduce the noise and redirect it away from sensitive areas. A bonus was that no doors were required.
Noise control measures such as these, if properly considered at the planning stage, will usually cost less than two percent of the initial capital costs of buildings and plant. The process begins with a proper understanding of the nature of noise and its abatement.
A fundamental element of acoustic planning is to recognise not only the noise sources, but also the natural noise barriers which might be available. Minimising noise problems might involve something as simple as using an existing structure to screen factory noise sources from residences.
Materials
Choice of materials can be an interesting factor in these situations. Whereas thick concrete walls tend to be the first choice for many people unfamiliar with acoustics, there are more appealing alternatives.
Years ago I was involved in developing a triple layer steel composite panel for walling and roofing of a large factory. The acoustically absorptive panel weighs just 90 kilograms per square metre and yet it could keep the sound of ships' horns out of the Sydney Opera House if it had to. Light and easy to erect, it comprises readily available profiled steel building products and common rock wool and glass fibre materials.
Sometimes the solution is an acoustic barrier, and these can at times be right at hand. Where extensive site excavation is required, the material can be used to create a noise-reducing embankment rather than being dumped off-site. With a little landscaping, this technique has significant aesthetic appeal in addition to its financial and acoustic benefits.
Other screening measures can include using a quiet area such as a canteen, store or office block as a barrier between the noise and the residences. Location of these areas is often arbitrary in the design stages, so using them as sound barriers may not compromise other aspects of a plan. At the same time, these areas tend to be the most visually attractive, and the sound-sensitive frontages will generally be the most visible. Their location therefore tends to make aesthetic sense as well as acoustic sense.
Acoustic Enclosures
Beyond these simple measures, it may be necessary to install ventilated acoustic enclosures for machines, or to fit silencers to noisy equipment.
Ventilation and ducting can offer great potential for savings. Consider the case of a large duct carrying furnace gas and dust away to an air cleaning plant. Originally designed to run 20 metres overhead, it had an unobstructed opportunity to radiate sound over a wide area. Muting its noise would have been massive challenge by any standard.
The solution, though, was simple. Against all established practice for such ducts, the gases were diverted into an underground tunnel, so the noise was absorbed by the ground instead of being radiated into the air. Not only did this overcome the noise problem at modest cost, but it allowed dust and grit build-up to be removed by lifting a cover and driving a bobcat through the duct, rather than expensive manual cleaning.
Sometimes the answer lies in plain hard work. A classic challenge was the case of quieting large cooling vents on a factory working with red-hot metal. Large sound attenuating panels had to be located in the air inlets and outlets, which added to airflow resistance, which required larger openings to decrease resistance, which then required larger panels to reduce the noise ... and so it went on. An iterative process produced a design to achieve both cooling and quietness without any "special technology". Not fancy, but very effective.
Heavy Vibrations
Isolating vibration is another important consideration at design stage. Once a vast block of reinforced concrete has been cast into a floor, and a massive piece of equipment is mounted on it, it is too late to consider isolation. And yet vibration of this type can be isolated economically at the outset. The simple expedient of separating the block from other elements, such as floors or walls, can be enough to overcome transmission problems before they arise.
Smaller vibration sources can be hard to trace, but they are usually easier to fix. Vibrations from refrigeration or air compressors can be transmitted by panels, piping or other fittings and converted into offensive noise. The simple task of identifying all these smaller sources and isolating them at the design stage can eliminate such problems before they arise.
Machine Noise
Managing noises at the planning stage can be a particularly satisfying acoustic exercise. Even a simple measure, such as using plate construction instead of open-sided machine frames, can achieve considerable noise reduction. Designers who consciously consider noise control will often produce better machines and sometimes at lower costs. The acoustic benefits alone will result in more contented operators.
Sometimes the solution to an equipment noise problem just takes a little lateral thinking - literally. Much of the noise created by high speed can or bottle runs is caused by the clanking of cans and bottles together. Using lower speed multiple or parallel path conveyors can achieve major noise reductions with no reduction in total work flow.
Eliminating gaps and openings in panels is a vital aspect of noise attenuation. The most common gaps are in the joints between wall panels, and where the walls meet the floor or ceiling. The noise reduction rating of a wall panel may be reduced by half because of gaps as small as 0.5 per cent of the total wall area. Even without panel gaps, this could easily occur where there are many ducts, pipes or electrical conduits passing through a wall. Yet all it takes to avoid such problems is to seal or caulk all holes, gaps and joints.
At every turn the message in noise abatement is the same: plan early and it can be both simple and inexpensive. Perhaps in no other discipline is there as much satisfaction to be had from implementing relatively simple engineering principles at the outset of a project. At this stage the only sounds are the rustling of drawing paper or the click of a mouse, but this is the best time to save the most.
By John Mazlin
John Mazlin is the principal of Camets consulting acoustical and vibration engineers, specialising in assessment, analysis, design, implementation and construction. Phone 02 9891 4522 or email john@camets.com.au.
