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TOP 10 NOISE CONTROL TECHNIQUES

The following are 10 simple noise control techniques that have wide application across the whole of industry. In many

cases, they will produce substantial noise reductions quickly and cheaply - with little or no effect on normal operation

or use.

1 DAMPING

Typical applications

Chutes, hoppers, machine guards, panels, conveyors, tanks . . . . .

Technique

There are 2 basic techniques:-

— unconstrained layer damping where a layer of bitumastic (or similar) high damping material is

stuck to the surface

— constrained layer damping where a laminate is constructed

Constrained layer damping is more rugged and generally more effective. Either remanufacture

steel (or aluminium) guards, panels or other components from commercially

available sound deadened steel or buy self adhesive steel sheet. The latter can simply be

stuck on to existing components (inside or outside) covering about 80% of the flat surface

area to give a 5 - 25 dB reduction in the noise radiated (use a thickness that is 40% to 100%

of the thickness of the panel to be treated).

Limitations : the efficiency falls off for thicker sheets. Above about 3mm sheet

thickness it becomes increasingly difficult to achieve a substantial

noise reduction.

2 FAN INSTALLATIONS

Typical applications

Axial flow or centrifugal fans.

Technique

Maximum fan efficiency coincides precisely with minimum noise. Any fan installation feature

that tends to reduce fan efficiency is therefore likely to increase noise. Two of the most

common examples are bends close to the fan (intake side in particular) and dampers (close to

the fan intake or exhaust). Ideally, for maximum fan efficiency and minimum noise, make sure there is at least 2 - 3 duct

diameters of straight duct between any feature that may disturb the flow and the fan itself.

Noise reductions of 3 - 12 dB are often possible.

3 DUCTWORK

Typical applications

Extraction, ventilation, cooling, openings in walls and enclosures.

Technique

Instead of fitting silencers, it is often possible to achieve a 10 - 20 dB reduction in airborne

noise from a duct or opening by lining the last bend in the ductwork with acoustic absorbent

(foam or rockwool / fibreglass). Alternatively, construct a simple absorbent lined right-angled

bend to fit on the opening. Ideally, either side of the bend should be lined along a length

equivalent to twice the duct diameter. Where flow velocities are high (> 3m/s), consider using

cloth faced absorbent. Duct vibration can usually be treated by damping (as above).

4 FAN SPEED

Typical applications

Axial or centrifugal flow fans.

Technique

Fan noise is roughly proportional to the 5th power of fan speed. So in many cases it is

possible to achieve a large noise reduction from a small drop in fan speed by changing

control systems or pulley sizes and re-setting dampers. The following table provides a guide

to the trade-off that can be expected.

5 PNEUMATIC EXHAUSTS

Note : a well designed silencer will not increase system back pressure.

Almost invariably it is possible to reduce pneumatic exhaust noise permanently by 10 - 30 dB

by fitting effective silencers. The following are the practical points that can make the

difference between success and failure:-

— back pressure : fit a larger coupling and silencer

— clogging : fit a straight-through silencer that cannot clog (and has no

back pressure)

— multiple exhausts : manifold them into a single, larger diameter pipe

fitted with the rear silencer from virtually any make of

car (from your local tyre and exhaust fitter). Typically

25 dB reduction.

6 PNEUMATIC NOZZLES

Typical applications

Cooling, drying, blowing . . . . .

Technique

In most cases, it is possible to replace existing nozzles (usually simple copper pipe outlets)

for quiet, high efficiency units. These not only reduce noise levels by up to 10 dB, but also

use less compressed air. The types of nozzle to look out for are entraining units (schematic

below) from various manufacturers and in a variety of sizes.

7 VIBRATION ISOLATION PADS

Typical applications

Machine feet, pumps, mezzanine installations . . . . .

Technique

Mounting motors, pumps, gearboxes and other items of plant on rubber bonded cork (or

similar) pads can be a very effective way of reducing transmission of vibration and therefore

noise radiated by the rest of the structure. This is particularly the case where vibrating units

are bolted to steel supports or floors. However, a common error with the use of these pads is

for the bolt to ”short-circuit” the pad, resulting in no isolation. Additional pads must be fitted

under the bolt heads as shown below.

There are many types of off-the-shelf anti-vibration mounts available, for instance

rubber/neoprene or spring types. The type of isolator that is most appropriate will depend on,

among other factors, the mass of the plant and the frequency of vibration to be isolated. Any

supplier of anti-vibration mounts will be able to advise you on this.

8 EXISTING MACHINE GUARDS

Technique

The existing guards on many machines can often be improved to provide a significant noise

reduction. The two principles involved, which must be used in combination, are:-

(i) Minimise gaps

Reducing by half the “gap” open area in a set of guards can reduce the noise by 3

dB. If you can reduce the openings (flexible seals, additional close fitting panels etc)

by 90%, then a 10 dB noise reduction is possible.

(ii) Acoustic absorbent

Lining a significant proportion of the inside of the guards with acoustic absorbent

(foam, rockwool / fibreglass) will reduce the noise “trapped” by the guards.

Consequently, less noise will escape through any gaps. Failure to line the inside of

the guards could result in an increase in noise at the operator’s position if the gaps

have been minimised as in (i) above.

In most cases, both sets of modifications can be tested in mock-up form using cardboard (and

wide tape) to extend the guarding and temporarily fitting areas of acoustic foam inside. Not

only does this process help with the practical aspects (access, visibility etc), but it usually also

provides a very good indication of the noise reduction that can be expected. Very “Blue

Peter” but very effective. Guard vibration radiated as noise can also be treated via damping

(as above).

9 CHAIN AND TIMING BELT DRIVES

Technique

Noisy chain drives can often be replaced directly with quieter timing belts. Within the range of

timing belts available, there are also quiet designs that use different tooth profiles to minimise

noise. There is also a very new design of belt for applications where noise is critical which

uses a chevron tooth pattern to provide very quiet running. Noise reductions in the range of 6

- 20 dB are often possible using this approach.

10 ELECTRIC MOTORS

Technique

Most companies have large numbers of electric motors used on anything from fans to pumps

to machine tools. However, it is not very common knowledge that general duty motors are

available (at little or no cost premium) that are up to 10 dB(A) or more quieter than typical

units as direct replacements. The best approach is to feed these motors into the system over

a period of time so that all replacement motors are quiet motors.

This sheet was produced by the Engineering Industry Noise Task Group (see

http://www.hse.gov.uk/noise/who.htm) with the grateful assistance of Peter Wilson of the

Industrial Noise and Vibration Centre (INVC).

Noise Control

Noise Paths
Noise in buildings may take many paths. The following figure illustrates the possible paths.

Noise Levels
As discussed in the perception of sound levels, the human hearing system has different sensitivities at different frequencies. This means that the perception of noise is not equal at all frequencies. Noise with significant measured levels (in dB) at high or low frequencies will not be as annoying as it would be when its energy is concentrated in the middle frequencies. In other words, the measured noise levels in dB will not reflect the actual human pereception of the loudness of the noise. A specific circuit is added to the sound level meter to correct its reading in regard to this concept. This reading is the noise level in dBA. The letter A is added to indicate the correction that was made in the measurement.
The following table displays A-weighted sound levels for some common noises:

TL, STC and IIC
The transmission loss (TL) for a partition and the noise reduction in the room are defined in the following drawing and demonstrated in the program NoiseControl2D.

Sound transmission class (STC) is a single number used to characterize the air-borne isolation properties of a partition. The STC is determined from the measured TL of a partition at different frequencies. These measured values are then compared with standardized STC contours as shown in the "examples" page. Simple rules apply in choosing the appropriate contour. For example: STC for painted concrete block depends on its weight, but will be in the range of 45-47 for 8", and of 47-51 for 12".
The STC of the composite partition (wall and window for example) is not the sum of the STC of its components. We have first to calculate the TL for the composite wall (taking into account the surface area of the components) then find the STC rating. STC and compsite STC calculations is provided in NoiseControl2D program. Sketch of the calculations is provided in the "examples" page
Impact isolation class (IIC), like STC, is another single-number rating system for a solid-borne noise (floor-ceiling structure). The higher the IIC rating, the more efficient the construction will be in attenuating the impact sound within the frequency range of the IIC. For example: 6" reinforced concrete slab (75 lb/sq ft) has IIC 34, and about 37 when linoleum is added to the floor.

Community Noise (Leq , Ldn, L10, L50, L90)
Community noise constantly changes its level and duration. It can reach 50 dBA changes in short time. The following are some of the A-weighted quantities used in measuring the effects of environmental noise:
Equivalent sound level (Leq) is a steady-state sound that has the same energy and A-weighted level as the community noise over a given time interval.
Day-night averaged sound level (Ldn) is the 24-hour Leq obtained after addition of 10 dBA to the sound levels from 10 P.M. to 7 A.M.
10 percentile-exceeded sound level (L10) (L50, L90 can be used) is the A-weighted sound level happened at 10% or more of the time of the measurement (or 50%, 90% in case of L50, L90).
There are many other different quantities used in the community noise measurements (such as Ln and CNEL). The criteria of evaluating the community noise can be given in any of these quantities. These criteria include more details for studying the community noise, and they depend on the local regulation and the type of the noise.

Room Noise (NC, RC, NCB)
Noise in buildings is more stable (over time) than outside community noise. The maximum acceptable background noise level generated by the mechanical systems in buildings is usually specified in terms of average A-weighted sound levels, NC, RC, or NCB.
The noise criteria (NC) values are determined from the measurements of the octave-band sound levels in an occupied room when the air-conditioning system is on. The measured values are then compared to standard NC curves.
The room criterion (RC) is mostly used for acoustical design of HVAC systems. The RC criteria take into account the noise components at the lowest and the highest frequencies. The measurement values should be taken in an unoccupied room.
Another criterion called balanced noise criterion (NCB) has been recently standardized and has concepts similar to NC and RC. The sound level measurements for NCB should be taken in an occupied room. The RC and NCB ratings include procedures for checking different factors such as the rumble compliance (excessive noise at frequencies below 500 Hz) and the hiss compliance (excessive noise at frequencies above 1000 Hz).

Noise publications

Posters

• Living Sustainably — For a Healthy Environment (1996)

Brochures/Leaflets

• Dealing with neighbourhood noise (brochure; June 2004) neighbourhod_noise.pdf (327kb)
• Dealing with barking dogs (brochure; June 2004) barking_dogs.pdf (272 kb)
• Managing noise from vehicles (brochure; June 2004) vehicle_noise.pdf (333 kb)
• Managing noise from intruder alarms (brochure; June 2004) intruderalarm.pdf (337 kb)
• Seeking noise abatement orders to prevent offensive noise (brochure; June 2004) noise_abatement.pdf (221 kb)

Back to top

Guidance/Advice

• Noise Guide for Local Government (June 2004)
  • Parts 1-5 (NGLGparts 1_5.pdf 1331 kb)
  • Part 6 Appendixes 1-6 (NGLGappendix1_6.pdf 1491 kb)
  • Part 7 (NGLGpart7.pdf 23 kb)
• Motorcyle muffler labelling in NSW (June 2004)
• Environmental Criteria for Road Traffic Noise (June 1999) (roadnoise.pdf 279 kb)
• Environmental Noise Management - NSW Industrial Noise Policy (December 1999) (Policy ind_noise.pdf 276 kb 62 pages, Appendices ind_noise_app.pdf 231 kb, 49 pages)

Non-EPA publications available from the EPA

• Air Conditioner Noise: Buying an air conditioner? Then protect your investment and buy one that will not intrude on your neighbours (1989) (Australian Environment Council)

If you want the BEST, you have come to the right place! We carry everything for Noise Control and Soundproofing from: Sound Booths, Acoustic Foams, Sound Blocking Vinyl Barriers, and other High Performance Noise Control Materials! ArtUSA Acoustics is your one-stop-shop all of your acoustic products needs. Have any questions? You are always welcome to contact our knowledgeable and friendly staff. Discover for yourself why ArtUSA Acoustics is the most trusted name in the industry. ArtUSA Noise Control Products Inc. is a company with 25 years of experience and over 500 specialty soundproofing, noise control, vibration control and acoustical products. We have knowledgeable acoustics and soundproofing professionals ready to explain our cost effective solutions. With hundreds of products in stock, easy to use, fast shipment.. ArtUSA Noise Control Products Inc. offers a complete line of soundproofing and noise control products for use in many applications. Our soundproofing products provide noise control for broadcast and recording studios, classrooms and home theaters. We provide excellent information on sound reduction for architectural acoustics. Our soundproofing products are available for industrial noise control and residential sound reduction too. Soundproofing and acoustical treatments can be applied almost everywhere. ArtUSA Noise Control, Inc. offers the widest product selection in the soundproofing industry with solutions for every type of noise problem. Our expert staff is available to help meet your needs, offering excellent advice on noise control product selection and installation. Noise Control Solutions with Industrial/Environmental Acoustic Enclosure Systems for Fans, Blowers, Pumps, Generator Sets, Test Chambers, Grinders, Dryers, Processes, Compressors, Saws, Quench Operations, Conveyors, Chillers, Shakers, Vibratory Feeders, Condensors, Process Equipment, Presses, Water Jet Cutters, Granulators, Shredders, Parts Washers, Swedgers, Milling Machines. The information provided in this part of our website is presented in an effort to help you in understanding acoustics (the science of sound) and how it affects you in everyday life. Learning the basics of acoustics will help you select products and methods to better solve your sound and noise problems. Certain words and phrases throughout the Acoustical Solutions website are highlighted so that you may go directly to the definition in the university or glossary and terms page  to help gain a better understanding of the product information. As always, you may contact one of our sales representatives by phone at 1-888-454-6975 or by email at franka@noisecontrolproducts.com  to answer your questions and help you build a solution that best fits your needs.

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