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
1.0Introduction 3
1.1definition of noise 3
1.2effects of outdoor noise 3
1.2.1human health effects 3
1.2.2environmental effects 3
1.3How is outdoor noise control beneficial? 4
1.4Sources of outdoor noise 4
CHAPTER TWO
2.0Outdoor noise control 5
2.1natural noise control 5
2.1.1Sound wave spreading with distance 5
2.1.2Absorption of sound by the atmosphere 6
2.1.3Ground effect 6
2.1.4Wind and temperature gradient effects 7
2.2Noise control at the source, along the path and at the receiver 8
2.2.1Noise control at the source 8
2.2.2Noise control along sound path 9
2.2.2.1blocking the sound path- barriers and buffers-9
2.2.3Noise control at receiver- 11
A)Residential outdoor noise control- insulation priorities 12
B)Reducing noise exposures on high-rise balconies 13
2.2.3.1Soaking up noise with sound absorbing materials-14
2.2.3.2Controlling noise by controlling vibration- Damping materials 14
Conclusion - 15
References - 15
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 benefitfrom. There are few places on the planet where in our daily liveswe are free from unwanted sounds.
Noise from many outdoor sources assails our hearing as itinvades our homes and work places: traffic, aircraft, barkingdogs, neighbours’ voices. Noise within the workplace—fromoffice machines, telephones, ventilating systems, unwantedconversation in the next cubicle—distracts us from our workand makes us less productive.
Noise can frustrate and impede speech communication. It canimperil us as we walk or drive city streets. It can be a physicalhealth hazard as well: exposure to high noise levels can causepermanent 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.
1.1Definition of noise
Noise is often defined as unwanted sound. It has human and environmental health effects and iselaborated as follows:
1.2EFFECTS OF OUTDOOR NOISE
1.2.1Human health effects
Noise health effects are both health and behavioural in nature. Noise can damage physiologicaland 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 canlead 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 tocardiovascularproblems and exposure to moderately high levels during a single eight hour period causes astatistical rise in blood pressure of five to ten points and an increase in stress andvasoconstriction leading to the increased blood pressure noted above as well as to increasedincidence of coronary artery disease. Outdoor noise is also a well known cause of annoyance and reduced ability to concentrate.
1.2.2Environmental effects
Noise can have a detrimental effect on animals by causing stress, increasing risk of mortality bychanging the delicate balance in predator/prey detection and avoidance, and by interfering withtheir 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 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 andpsychological 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 tocheck outdoor noise.
1.3How 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 addstress that eventually leads to heart disease. If these guidelines of control are implemented it can ameliorate suchconditions to a certain extent.
1.4SOURCES 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.)Noise from traffic, rail, automobiles and aircraft
2.)Noise from construction sites
3.)Noise from built up areas (industry, commerce , offices, and public buildings)
4.)Noise from neighbouring spaces and social gatherings
5.)Noise from mechanical equipments
Fig1:decibel scale –
Showing sound levels typically created by
Familiar sources of noise in the
home and environment.
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
2.1NATURAL 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.
2.1.2Absorption 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 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 low-frequency 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
2.1.3Ground 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.
2.1.4Wind 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.
2.2Noise 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
2.2.1Noise 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.
2.2.2Noise 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).
2.2.2.1BLOCKING 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:
- 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
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
B)Buffers
Buffers can reduce noise from roads and other sources tolevels that allow normal outdoor activities to occur. A 100-footwide planted buffer will reduce noise by 5 to 8 decibels (dBA).
Using a barrier in the buffer such as a landform cansignificantly increase buffer effectiveness (10 to 15 dBAreduction 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 anappropriate 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 noisebarriers where possible.
2.2.3Noise 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.
Fig9:Using building configuration to exclude traffic noise
Fig10: Using floor plans configuration to exclude traffic noise
A)Residential outdoor noise control- insulation priorities