ARC 507 –BUILDING SERVICES III (ACOUSTICS)
NOISE CONTROL OUTDOORS
COMPILED BY
EWANLEIFOH NEAL .O – ARC/09/7379
AND
ESO SUNDAY OLUWAFEMI – ARC/09/7377
JULY 2014
SUBMITTED TO
THE DEPARTMENT OF ARCHITECTURE
FEDERAL UNIVERSITY OF TECHNOLOGY
AKURE
NOISE CONTROL OUTDOORS-TOPIC 18
ABSTRACT
This write up examines the effect of outdoor noise on human, environmental health and the
residential or working environment, it also identifies the common sources of this form of
noise and then proffers guidelines to controlling them.
TABLE OF CONTENTS
Title
page
CHAPTER ONE
1.0
Introduction
1.1
definition of noise
1.2
effects of outdoor noise
1.2.1 human health effects
1.2.2 environmental effects
1.3
How is outdoor noise control beneficial?
1.4
Sources of outdoor noise
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3
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4
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CHAPTER TWO
2.0
Outdoor noise control
2.1
natural noise control
2.1.1 Sound wave spreading with distance
2.1.2 Absorption of sound by the atmosphere
2.1.3 Ground effect
2.1.4 Wind and temperature gradient effects
2.2
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6
6
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Noise control at the source, along the path and at the receiver
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2.2.1
2.2.2
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Noise control at the source
Noise control along sound path
2.2.2.1 blocking the sound path- barriers and buffers-9
2.2.3
Noise control at receiver- 11
A)
Residential outdoor noise control- insulation priorities
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B)
Reducing noise exposures on high-rise balconies
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2.2.3.1 Soaking up noise with sound absorbing materials-14
2.2.3.2 Controlling noise by controlling vibration- Damping materials
Conclusion References -
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CHAPTER ONE
1.0
INTRODUCTION
We live in a noisy world. Twenty-four hours a day, seven days a week, we are exposed to
sounds we do not want, need, or benefit from. There are few places on the planet where in
our daily lives we are free from unwanted sounds.
Noise from many outdoor sources assails our hearing as it invades our homes and work
places: traffic, aircraft, barking dogs, neighbours’ voices. Noise within the workplace—from
office machines, telephones, ventilating systems, unwanted conversation in the next
cubicle—distracts us from our work and makes us less productive.
Noise can frustrate and impede speech communication. It can imperil us as we walk or drive
city streets. It can be a physical health hazard as well: exposure to high noise levels can cause
permanent hearing loss.
In short: Noise is unwanted sound.
Outdoor noise control involves devising means to attenuate or impede the propagation or
intrusion of sound from outdoor sources into a working or residential spaces. Various means
would be studied which include, natural noise control, control of outdoor noises at the
source, control at the transmission path and also control at the receiver.
1.1
DEFINITION OF NOISE
Noise is often defined as unwanted sound. It has human and environmental health effects and
is elaborated as follows:
1.2
EFFECTS OF OUTDOOR NOISE
1.2.1 Human health effects
Noise health effects are both health and behavioural in nature. Noise can damage
physiological and psychological health. Noise pollution can cause annoyance and aggression,
hypertension, high stress levels, tinnitus, hearing loss, sleep disturbances, and other harmful
effects. Furthermore, stress and hypertension are the leading causes to health problems,
whereas tinnitus can lead to forgetfulness, severe depression and at times panic attacks.
Chronic exposure to noise may cause noise-induced hearing loss. High noise levels can also
contribute to cardiovascular problems and exposure to moderately high levels during a single
eight hour period causes a statistical rise in blood pressure of five to ten points and an
increase in stress and vasoconstriction leading to the increased blood pressure noted above as
well as to increased incidence of coronary artery disease. Outdoor noise is also a well known
cause of annoyance and reduced ability to concentrate.
1.2.2 Environmental effects
Noise can have a detrimental effect on animals by causing stress, increasing risk of mortality
by changing the delicate balance in predator/prey detection and avoidance, and by interfering
with their use of sounds in communication especially in relation to reproduction and in
navigation. Acoustic overexposure can lead to temporary or permanent loss of hearing in
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animals as well. The noise levels in Hyderabad are above the mandated safe norms in most of
the areas. Noise effects are both health and behavioural in nature and can damage
physiological and psychological health. This implies that there is an urgent need to take
measures to protect residents from unwanted sound and its impacts. This study therefore
attempts to proffer means to check outdoor noise.
1.3
HOW IS OUTDOOR NOISE CONTROL BENEFICIAL?
Noise pollution causes hearing losses over time. It can also cause tinnitus, a ringing sound in
the ears. Too much noise often makes one tired, nervous and unable to concentrate. It can
raise blood pressure and add stress that eventually leads to heart disease. If these guidelines
of control are implemented it can ameliorate such conditions to a certain extent.
1.4
SOURCES OF OUTDOOR NOISE
There are various sources of sound in the environment of which produce sound of different
sound levels (measured in decibels dBA). In order to control noise from these sources , it is
imperative one identifies these sources and determine the level of sound produced ,this is
done with a sound level measuring instrument e.g. a sound level meter , which consequently
determines the measure of control to be employed.
The major sources of outdoor noise are listed below:
1.)
2.)
3.)
4.)
5.)
Noise from traffic, rail, automobiles and aircraft
Noise from construction sites
Noise from built up areas (industry, commerce , offices, and public buildings)
Noise from neighbouring spaces and social gatherings
Noise from mechanical equipments
Fig1: decibel scale –
Showing sound levels typically created by
Familiar sources of noise in the
home and environment.
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CHAPTER TWO
2.0.
OUTDOOR NOISE CONTROL
Outdoor noise control involves the means of attenuating or impeding the propagation or
intrusion of sound from outdoor sources Such as, traffic, industries etc into a working or
residential spaces. There are various forms of noise control of which when properly applied
are able to ensure a serene working or living environment.
The forms of outdoor noise control include:
1.)
Natural noise control
2.)
Noise control at source,
3.)
Noise control along the transmission path
a) Blocking the sound path – Buffers and Barriers
4.)
Noise control at the receiver
a) Soaking up noise – sound absorbing materials
b) Controlling noise by controlling vibration – damping materials
2.1 NATURAL NOISE CONTROL
As sound waves move out from the source, their intensity (loudness) steadily decreases due
to several natural phenomena. Two of these (geometric wave spreading and air absorption)
are always present to some degree, while three others (ground effect and wind and
temperature gradient effects) occur only under certain, fairly common conditions. These
phenomena are described below.
2.1.1 Sound wave spreading with distance
In the same way that a balloon is stretched thinner and thinner as it is blown up, sound waves
become weaker and weaker as they travel outward from their source and their energy is
spread over larger and larger areas. This concept is illustrated in Figure 2. For “point”
sources of sound (that is, sources that are physically small compared to the listener’s
distance from them) such as an aircraft in the sky or an ambulance siren, this spreading is
spherical (think of an expanding round balloon) and causes sound levels to decrease at a rate
of 6 dB per doubling of distance. Due to this spherical spreading, noise from point sources
becomes at least 35% quieter with each doubling of distance. When the sound source region
is large compared to the distance to the listener’s position, sound levels decrease more
gradually. For example, traffic on a busy roadway represents a “line source” of sound from
which sound waves spread out cylindrically (think of the expansion of a long, thin “party”
balloon). Sound levels from a line source decrease at 3 dB per doubling of distance – or half
the rate of point sources. In typical urban settings where setback distances are limited,
geometric spreading generally accounts for most of the natural sound attenuation between
noise sources and receivers.
2.1.2 Absorption of sound by the atmosphere
As sound waves pass through the atmosphere, they lose energy as they “jostle” the air
molecules. This is a gradual process that depends on air temperature and humidity. Over the
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limited source-to-receiver distances typically experienced in the city, atmospheric absorption
has very little effect. Over larger distances (100 m or more), it can begin to reduce overall
noise levels as well as alter the character of complex sounds (such as traffic noise). This is
because air absorption attenuates high-frequency components much more rapidly than lowfrequency ones and this is why the noises from distant traffic, trains, industries or jet aircraft
tend to have a low, “rumbling” character.
Fig2: Spreading of sound waves
from point and line sources
2.1.3 Ground effect
A third source of natural noise attenuation called “ground effect” occurs when sound waves
pass close to soft, porous ground surfaces (lawns, fields, forest floors) on their way from the
source to the receiver. This effect (which is caused by the local cancellation of direct and
ground-reflected sound waves) can be large, particularly at distances of more than 100 m or
so and when both the noise source and receiver (listener) are located close to the ground. In
extreme cases where the listener is separated from a busy roadway by a wide, flat stretch of
soft terrain, the ground effect can render noise from this roadway virtually inaudible over
other contributors to urban hum. Even at typical smaller distances (10 to 15 m) across urban
lawns or boulevards, the effect can be significant for receivers near ground level. There is
then some benefit to be obtained from retaining or installing soft surfaces (e.g., lawns,
gardens or flower beds) between a roadway, or other noise source, and one’s residence.
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2.1.4 Wind and temperature gradient effects
When wind blows against the direction of sound travel (i.e. from the noise receiver location
towards the noise source location) it causes sound waves to bend upwards away from the
earth’s surface (see Figure 3A). This can create a “sound shadow” (i.e., a zone of quiet) at
large distances. When the wind blows in the same direction as the sound (i.e., from the noise
source towards the receiver), sound waves are bent down towards the earth (see Figure 3B).
Where the intervening ground is “soft” so that ground effect is possible, or where some sort
of noise barrier is present, this downward bending of sound waves can substantially increase
the level of noise reaching distant receivers. However, at the short setback distances typical
of most urban noise situations, the most significant effect of wind is to raise background
noise levels, thereby potentially masking intrusive noises.
Strong air temperature gradients can cause similar sound-bending effects. In particular,
during clear, calm nights, the air is often colder near the ground than higher up. Under such
“temperature inversion” conditions, sound waves bend downwards towards the ground
giving rise to the common perception that distance sound sources are louder at night, a
perception that may also occur because “background noise” levels from common noise
sources such as traffic tend to be reduced at night. During normal daytime “temperature
lapse” conditions (i.e., when air is warmer near the ground), sound is bent upwards, away
from the ground so that, under calm conditions, sound shadows may occur in all directions
from the source.
Figure 3: Effects of wind and air temperature gradients on sound propagation
In general due to the above factors, maintaining an effective distance from the source of
sound would result in considerable sound attenuation.
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2.2
NOISE CONTROL AT THE SOURCE, ALONG THE PATH AND AT THE
RECEIVER
All community noise situations involve one or more noise sources, one or more noise paths
and one or more noise receivers. In planning for effective noise control, it is then useful to
consider opportunities that may exist to control noise at each of these three stages of its
transmission. Figure 4 illustrates the opportunities that generally exist to control noise at
these three stages in the context of a residence located near a busy road.
FIGURE 4: Traffic noise control options at the noise source, along the path and at the
receiver
2.2.1 NOISE CONTROL AT THE SOURCE
Noise control at the source typically involves avoiding generation of excess noise through
selection of inherently quieter equipment, regular maintenance and sensible operation.
Examples of inherently quieter equipment are busses manufactured in some European
countries under stricter noise emission regulations than apply to local buses and leaf blowers
designed to meet a noise limit of 65 dBA at 15 m. Source control may also involve
preventing noise from escaping from the source by adding appropriate control devices such
as mufflers, covers or enclosures. For many prominent urban noise sources, such as arterial
traffic, railways, aircraft and industry, source control measures are not in the hands of
individual residents.
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2.2.2 NOISE CONTROL ALONG THE SOUND PATH
Once noise has been created and has escaped from the source, there are various ways to
prevent it from reaching noise sensitive areas. These may include noise barriers located close
to the noise source (e.g., screens or partial enclosures around localized sources such as heat
pumps, and walls, earth berms or non-sensitive buildings along a highway) or close to the
noise receiver (e.g., a solid fence, earth berm or outbuilding on the noisy side of a residence
to shield sensitive indoor spaces or a solid fence or screen to protect outdoor recreation
areas).
2.2.2.1 BLOCKING THE SOUND PATH – BARRIERS AND BUFFERS
A) Barriers
The most familiar means of reducing residential exposures to noise
from road traffic or industrial sources is to erect a noise barrier
of some sort between the sound source and the receiver.
Noise barriers most often take the form of vertical walls,
but other types (such as earth berms, berm/wall combinations
and buildings) are also used.
An effective noise barrier must meet the following three requirements:
1. It must be tall enough and long enough to clearly block the line of sight from the
noise receiver to the noise source zone. For free-flowing arterial traffic, tires are
the dominant noise source, so that the source zone is close to the pavement where
it can often be shielded by barriers of moderate height. Where average speeds are
lower, and particularly where the heavy truck mix is high, engine and exhaust
noise are also important and, to be effective, noise barriers must be higher,
2. It must be dense (heavy) enough and be free from gaps and cracks so that there is
no significant transmission of sound through it,
3. It must be continuous throughout the noise source zone. For example, a traffic
noise barrier will not be effective if it must be frequently interrupted to
accommodate walkways or driveways.
FIG 5: the effect of barrier on sound waves
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Noise barriers can be made of almost any solid, reasonably heavy and durable material. The
materials most commonly used for noise barriers include: Pre-cast concrete posts and panels,
Concrete block, Corrugated steel panels and steel posts, Timber posts and planks , wall
fences etc.
The above noise barriers have acoustically “hard” surfaces which reflect (bounce) most of the
sound energy back in the general direction that it can from. That is, they do not absorb or
“destroy” much of the noise but simply redirect it away from the most noise-sensitive areas.
Sound-absorbing noise barriers are available however.
FIG 6: typical barrier walls
Fig 7: Effective residential noise barrier configurations
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B) Buffers
Buffers can reduce noise from roads and other sources to levels that allow normal outdoor
activities to occur. A 100-foot wide planted buffer will reduce noise by 5 to 8 decibels (dBA).
Using a barrier in the buffer such as a landform can significantly increase buffer effectiveness
(10 to 15 dBA reduction per 100-foot wide buffer with 12-foot high landform).
FIG 8: Arrangement of Buffer for noise control
Key design considerations
 Locate buffer close to the noise source while providing an appropriate setback for
accidents and drifting snow.
 Evergreen species will offer year-around noise control.
 Create a dense buffer with trees and shrubs to prevent gaps.
 Select plants tolerant of air pollution.
 Natural buffers will be less effective than planted buffers.
 Consider topography and use existing landforms as noise barriers where possible.
2.2.3 NOISE CONTROL AT THE RECEIVER
Noise control at the receiver (here, the residence) may involve the upgrading of windows,
doors, walls and, in some cases, roofs to better exclude noise from sensitive interior spaces.
It may also include the optimal location and configuration of the residence on the property to
minimize noise exposure (see Figures 9) and/or the design of the floor plan (see Figure 10)
which places less sensitive spaces closest to the noise source thereby creating a “buffer zone”
to reduce noise exposures within the more sensitive spaces such as living rooms and
bedrooms.
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Fig9: Using building configuration to exclude traffic noise
Fig10: Using floor plans configuration to exclude traffic noise
A)
Residential outdoor noise control- insulation priorities
Windows:
• provide airtight perimeter seals,
• locate larger windows on quiet side of house,
• use heavier glass and larger airspace between sheets of glass,
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Doors:
• use solid wood, solid core or insulated steel doors,
• provide airtight seals along top, bottom and sides,
• create an entrance vestibule (entryway or porch)
Walls:
• increase mass of lightweight constructions with additional interior layers of
gypsum board or heavy external materials such as cement stucco or brick,
• fully insulate cavities (with glass, mineral or cellulose fibre batts or loose-fill,
blow-in insulation),
B)
Reducing noise exposures on high-rise balconies
Noise levels on balconies are often amplified by the reflection of sound from the hard
surfaces provided by the underside of the balcony above, the back of the railing (if of solid
construction – i.e., not open bars) and the walls, windows and glass doors of the unit in
question. The application of weather-resistant sound absorbing material to these surfaces will
reduce noise levels both on the balcony and in adjoining rooms.
To reduce the amount of noise entering the high-rise residential unit, heavy curtains can be
hung across the glass doors and/or windows that open onto the balcony. Ideally these would
be of a impervious, (airtight) material such as the mass-loaded vinyl curtains.
Fig11: Limiting noise exposure on high-rise balconies and within adjacent rooms
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2.2.3.1
Soaking up noise with sound absorbing materials
Similar to most of the noise barriers described above, common building materials (e.g.,
concrete, brick, steel, timber, glass and gypsum board) are largely sound reflective, that is,
they throw back most of the sound energy that strikes them. In many cases such sound
reflections are not a problem because they do not significantly increase noise levels at any
sensitive receiver locations. However, in situations in which large building surfaces focus
reflected sound to sensitive areas it becomes necessary to use sound absorbing materials.
Most common sound absorbing materials are highly porous and can absorb 60 to 90% of the
sound energy that strikes them while some materials can absorb 95 to 99% of high-frequency
sound energy. The tiny pores and passages within such materials (e.g., heavy fabrics,
draperies, carpeting and upholstery, glass or mineral fibre insulation and open-celled foam
rubbers), permit sound waves to enter. In squeezing through these tiny passages, the energy
of the sound waves is dissipated – i.e., turned into heat.
2.2.3.2
Controlling noise by controlling vibration- Damping materials
Since sound is often produced and transmitted by vibrating objects, it makes sense that we
can control noise by controlling vibration.
When an operating power tool, appliance or power generator comes in contact with a large,
flexible surface such as a sheet of plywood, a table top, wall or a floor, its noise is amplified.
The amplification of noise from engines, electric motors, appliances or power tools can then
be avoided by eliminating any rigid contact between these devices and flexible surfaces such
as machinery enclosures, counter tops or the wooden floors and gypsum board walls of
residences. In practice this can be done by placing resilient rubber pads or matting beneath
appliances and the countertops or floors supporting them. Similarly, fans, pumps and motors
can be mounted on neoprene pads or steel springs to prevent their vibration and noise from
entering supporting floors and walls and spreading throughout the building.
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CONCLUSION
“Freedom from the harassing effects of noise is one of the finest qualities a building can
possess.’’ (Vern A Knudsen and Cyril M Harris, Acoustical consultant).
A building with great acoustics can improve productivity; ensure a convenient and
comfortable working environment, which is also safe health wise. This could be achieved by
employing one or a combination of two or more of the above examined outdoor noise control
methods, depending on the situation of the environment in question. It is often advisable to
apply control methods in chronological order as follows: control at source, control at
transmission path, and control at receiver. This is an attempt to ensure that the propagation of
the noise is controlled right from its origin, before it gets to the receiver.
Once an environment has achieved good acoustics , the users would not have to wonder if the
acoustician was ever there.
REFERENCES
 Noise Control in Buildings Guidelines for Acoustical Problem-Solving. © 2003
Certain Teed Corporation 10/03
 Sound smart City of Vancouver Noise Control Manual.
 6.4 Aesthetics and Visual Quality
 Outdoor Noise Barriers: Design and Applications: Tom Paige, P.Eng. Products
Application Engineer Kinetics Noise Control, Inc. Mississauga, Ontario.
www.enoisecontrol.com
 Environmental Building Guidelines for Greater Hyderabad — Ver. 1.2(2010)
 NPC special report This Quiet House Noise Control for the Home – Reducing the
Intrusion of Outdoor Sources
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