CHAPTER 4 NOISE POLLUTION

Definition

1. Frequency - is the number of cycles of vibration per second.

Symbol : f

2. Wavelength - distance between any two repeating points on a wave.

Symbol :

3. Velocity of noise distance of sound movement divided to time of sound movement

Symbol : v

Formula

The formula arises in fields from geology to astronomy to medicine.

The basic formula for wave velocity reads as follows: "wavelength x frequency =

wave velocity" where wavelength is in meters, frequency is in hertz (a unit of

frequency) and wave velocity is in meters per second.

v = f

The use of formula:

1. tells scientists how fast a wave is moving, which in turn allows them to

make predictions and conclusions about how various types of waves

work and can be manipulated

2. to calculate wavelength or frequency using simple algebra

Example:

Let's say the wavelength of a sound wave is 1.42m and the frequency is 260.71Hz.

In order to calculate the velocity of the sound wave we put these values into their

respective places in the wave velocity formula:

v = f

1.42m x 260.7Hz = wave velocity.

The answer is 370.21 m/s. This is the velocity of the sound wave.

Loud and Pitch

loudness is the quality of a sound that is primarily a psychological correlate of

physical strength (amplitude).

Pitch is an auditory perceptual property that allows the ordering of sounds on a

frequency-related scale

Unit of measure noise

Decibels, hertz, phons, mels and sones can all be used to measure sound levels.

Decible is a standard unit to measure sound

Standard unit for frequency is Hertz

Noise limit for certain environment condition

For hearing:

may be ranked as mild, moderate, moderately severe, severe or profound as defined

below:

1. Mild:

a) for adults: between 26 and 40 dB HL

b) for children: between 20 and 40 dB HL

2. Moderate: between 41 and 55 dB HL

3. Moderately severe: between 56 and 70 dB HL

4. Severe: between 71 and 90 dB HL

5. Profound: 90 dB HL or greater

Note that human hearing is relatively insensitive to low bass (below 100 Hz), and

also compresses at higher sound levels.

Here are some typical sounds, and their levels.

Sounds dB SPL

Rocket Launching 180

Jet Engine 140

Thunderclap, Air Raid Siren 1 Meter 130

Jet takeoff (200 ft) 120

Rock Concert, Discotheque 110

Firecrackers, Subway Train 100

Heavy Truck (15 Meter), City Traffic 90

Alarm Clock (1 Meter), Hair Dryer 80

Noisy Restaurant, Business Office 70

Air Conditioning Unit, Conversational Speech 60

Light Traffic (50 Meter), Average Home 50

Living Room, Quiet Office 40

Library, Soft Whisper (5 Meter) 30

Broadcasting Studio, Rustling Leaves 20

Hearing Threshold 0

The following are some subjective indications of the level of hearing loss:

1. 20 dB loss - hearing difficulty in an enclosed cinema.

2. 30 dB loss - hearing difficulty in the living room.

3. 50 dB loss - hearing difficulty on the telephone.

For speech

Noise can also interfere with our ability to communicate. In order to carry out a

conversation at normal distances, the sound level in a work place should be at most

65 to 70 dBA.

Noise significantly influences the ability to understand speech.

At around 70 dBA, for example, it is difficult to carry on a telephone conversation.

The interference (or masking effect) is a function of the distance between the

speaker and listener, and the frequency components of the spoken word.

Here are the SPLs for two persons talking (not shouting) at various differences (level

at the receiver's ear).:

0,25m 0,5m 1m 1,5m 2m 3m

70-76dB 65-71dB 58-64dB 55-61dB 52-58dB 50-56dB

Noise level for some point sources:

Source

Noise level dB(A) Source Noise level,

dB(A)

Air compressors 95-104 Quiet garden 30

110 KVA diesel

generator

95 Ticking clock 30

Lathe Machine 87 Computer rooms 55-60

Milling machine 112 Type institute 60

Oxy-acetylene

cutting

96 Printing press 80

Pulverize 92 Sports car 80-95

Riveting 95 Trains 96

Power operated

portable saw

108 Trucks 90-100

Steam turbine

(12,500 kW)

91 Car horns 90-105

Pneumatic Chiseling 118 Jet takeoff 120

Noise that disturb people- 1961-62 Central London Survey

No.

Description of

noise

No. of people disturbed per 100 questioned

When at

home

When

outdoors

When at work

1 Road traffic 36 20 7

2. Aircraft 9 4 1

3. Trains 5 1 0

4. Industry/construction

work

7 3 10

5. Domestic Appliance 4 0 4

6. Neighborhood

Impact

6 0 0

7. Children 9 3 0

8. Adult Voice 10 2 2

9. Radio/TV 7 1 1

10. Bells/Alarm 3 1 1

Basic component of sound level meter

Sound Level Meter is a device for measuring the intensity of noise, music, and

other sounds.

To take measurements, the SLM is held at arm's length at the ear height for

those exposed to the noise.

With most SLMs it does not matter exactly how the microphone is pointed at

the noise source.

The instrument's instruction manual explains how to hold the microphone.

The SLM must be calibrated before and after each use.

The manual also gives the calibration procedure.

Basic component of SLM

1. Microphone

picking up the sound and converting it into an electrical

The best instrument cannot give a result better than the output

from the microphone. Therefore, its selection and use must be

carefully carried out to avoid errors.

The output of a microphone is limited on the one hand by the

internal noise of the transducer and on the other hand by the

distortion resulting from high noise levels.

In addition, the instrument to which the output signal of the

microphone is fed will saturate if the signal is too high and will

also give a false result (that is, its background noise level) if the

signal is too low.

Therefore, high sensitivity microphones are needed to measure

very low noise levels (lower than 30 dB), and low sensitivity

ones have to be used for high noise levels such as for impact

noise (above 130 dB).

The dynamic range of typical good quality microphones is thus

between 100 and 120 dB.

The selection of the microphone is based on:

1. the levels to be measured,

2. the frequencies to be measured - low or high,

3. the type of acoustic field - free or diffuse,

4. the purpose and the type of measurement - overall

level or frequency analysis.

2. Amplifier

The electrical signal from the transducer is fed to the pre-

amplifier of the sound level meter

amplifies the signal and determines the RMS value of the signal.

Further amplification prepares the signal either for output to

other instruments such as a tape recorder or for rectification

and direct reading on the meter.

The rectifier gives the RMS value of the signal. The RMS signal

is then exponentially averaged using a time constant of 0.1 s

("FAST") or 1 s ("SLOW") and the result is displayed digitally or

on an analog meter.

3. Filter Frequency

divide the sound into separate frequency bandS

a sets of passive filters (octave or one third octave) that can be

inserted between the two amplifiers of the SLM.

Its can divide sound into separate frequency band

Other analyzers are specific instruments making it possible to

automatically scan the whole range of frequency bands. These

are sequential instruments making measurements in one band

at a time. This strongly restricts their use as the noise must be

constant both in amplitude and in frequency during the 5 to 10

minutes of the analysis.

More sophisticated analyzers have the possibility to make the

frequency analysis in all desired bands at the same time. These

are analyzers using a set of parallel filters or using the fast

fourier transform of the input signal before recombining the

data into the desired bands.

One important aspect to be considered about the filters is their

frequency characteristics.

Ideally, the filter should provide an attenuation of infinity

outside the band. In practice, this is never the case.

For most common filters, the attenuation at the cut off

frequencies is usually around 3 dB and is some 24 dB per

doubling of frequency outside that range

The practical implication of this is that a signal of 100 dB at

1000 Hz for instance will give a reading of 76 dB in the octave

bands centred at 500 Hz and 2000 Hz, although no energy is

present at frequencies covered by these two octave bands.

4. The instrument display

Read Out unit to display the sound level in dB

Contain meter or digital readout

Displays the answer as selected on the meter controls. In order

that average values can be displayed at 0 on the scale the

instrument's dynamic range is set at -5dB, +55dB relative to

scale zero.

In the OFF position, no functions are performed and there is no

drain on the instrument batteries. In the BATT position the

charge state of the lower of the two batteries is indicated on the

meter and as long as it indicates within the scale band marked

'Batt' there is sufficient power to operate the instrument to

specification. When in the ON position, the instrument carries

out its selected functions.

The answer to be displayed on the meter is chosen by the

setting of this control. In the SPL position the varying sound

level is displayed. When the Leq setting is selected the value

accumulated since reset for either equivalent continuous sound

level, Leq, the single event noise exposure level LAX, or the

takt maximum' value, LTm, as selected by switch 'e', is

displayed.

In order to read the maximum value logged during the

measurement sequence, the MAX position should be selected.

To enable a clear indication to be obtained, the instrument's

display range is split into two 30dB spans. Normally the lower

30dB is on scale. When this control is depressed, the upper

30dB is available, and hence, when it is activated, 30 must be

added to the displayed result to give the correct answer.

Effect of noise

i. Physical Damage to Ear

Exposure to sufficiently intense noise for a long enough duration results in

damage to the inner ear and thus decreases one's ability to hear.

In addition to a general decrease in the ability to detect sounds, the quality

and clarity of auditory perception can be affected, as well.

While these effects are often temporary, it is not uncommon for some residual

permanent damage to persist for the remainder of the affected person's life.

Whether temporary or permanent, hearing loss due to noise exposure

primarily affects the inner ear, especially when the noise is presented over a

significant period of time.

2.Blood Circulation System

A. Increase blood pressure

loud noise is suppose to cause consequent increase in blood pressure.

This leads in turn to smooth muscle hypertrophy, narrower lumen in

small vessels, and increased resistance to blood flow.

It can cause hypertension.

B. Gastric Change

exposure to 80 dB noise levels resulted in a reduction in stomach

contraction strength.

noise can lead to changes in one's gastrointestinal system. And

because gastric changes are related to ulcers, and because gastric

changes are related to ulcers noise may be related to ulcer

development, as well.

3. Psychological and emotional disorders

A. Effect on sleep

It is common knowledge that noise can disturb sleep (that's why we

use alarm clocks).

Its a common phenomenon in Malaysia that people living in heavy

traffic area are frequently awaken by noise at least "occasionally," and

since the volume of traffic has constantly increased substantially then,

it is likely that even more people are affected now.

Bugliarello et al. (1976) describe several factors that affect sleep

disturbance: factors involving the stimulus itself (e.g. type of noise,

repetition, duration, intensity, etc.), the stage of sleep at which the

stimulus occurs, and individual variables (e.g. state of health,

motivation to wake, etc.).

First, sleep disturbance by noise is affected by characteristics of the

noise itself.

For example, stimulus intensity is related to sleep disturbance, with

more intense stimuli awakening people more often.

However, disturbance thresholds vary widely among people, with some

people being disturbed by levels as low as 35 dB and others being able

to sleep through 90 dB levels.

And a person's threshold depends on the type of stimulus, as well. For

example, it appears that most people can sleep only 40 dB of street

traffic noise (Bugliarello et al., 1976).

Another factor affecting sleep disturbance is the stage of sleep during

which a noise occurs. In general, it requires greater intensity stimuli to

awaken people in the deeper stages of sleep.

Individual variables also affect noise's ability to awaken a person.

For example, lower intensities of noise are generally required to

awaken people as they grow progressively older. Thus, an elderly

person is more likely to be awakened by a given stimulus than a young

adult in a similar situation.

Additionally, motivation to wake must also be considered, as must a

person's state of health, since certain disorders (e.g. depression) are

known to affect sleep behavior.

B. Annoyance

One of the most salient effects of noise on humans is annoyance,

which Molino (1979) defines with the statement, "a noise is said to be

annoying if an exposed individual or a group of individuals would

reduce the noise, avoid, or leave the noisy area if possible" .

Annoyance due to noise depends on many factors, including several

parameters of the noise itself.

For example, louder noises are generally more annoying than quieter

noises , though two sounds with equal intensity (i.e. loudness) may

still result in different levels of annoyance.

Indeed, patterned sounds appear to be less annoying than sounds that

are randomly produced . Also, noises that are higher in pitch are

generally rated as more annoying than lower-frequency noise.

And finally, annoyance depends on the regularity of the noise. That is,

noises that remain constant in pitch and intensity are generally rated

as less annoying than noises that change in pitch or intensity.

Another factor affecting annoyance appears to be the source of the

noise. For example, it appears that noise produced by street traffic is

less annoying than equally-intense noise that is produced by aircraft,

an effect that was observed by Hall and colleagues (1981), as well. As

such, much of the research on noise-induced annoyance has focused

on aircraft noise

Additionally, the neighborhood that one is in is also important to

consider. That is, for a given noise exposure, annoyance is greatest in

rural areas, followed by suburban, urban, residential, commercial, and

industrial areas in decreasing order of annoyance. And noise appears

to be more annoying in the summer than in the winter (Miller, 1979a).

It is important to consider the influence of individual characteristics on

noise, especially attitude. According to Miller (1979a), "highly annoyed

persons are likely to believe that those responsible for the noise are

not concerned about those being exposed to the noise, and they are

also likely to believe that the source of noise is not of great importance

to the economic and social success of the community" (p. 137).

Additionally, "highly annoyed persons are likely to have negative

attitudes toward many kinds of noise; to be generally sensitive to

irritation produced by noise; to believe that their neighbors share their

annoyance; to say that they would be unwilling to accept further

increases in noise levels; and to believe that noise is a health hazard"

(pp. 137-138).

Further, it does not appear that annoyance due to noise pollution

exhibits habituation. That is, continued exposure to noise does not

appear to decrease annoyance. Rather, it appears that in some cases

continued exposure to noise actually increases annoyance (Abel, 1990;

Borsky, 1970).

In addition, it appears that the annoying effects of noise are cross-

cultural. Indeed, Abel (1990) states that there is "high similarity of

community reactions to changes in noise exposure level" and that the

annoying effect of noise "does not appear to be significantly influenced

by nationality".

C. Communication Interference

Noise pollution can have a considerable effect on communication.

According to Berglund and Hassmen (1996), "there can be no doubt

that noise can mask speech" .

And as Miller (1979a) points out, even when speech is accurately

understood, background noise may result in "greater pains on the part

of the talker and listener than otherwise would be needed" .

Many factors contribute to the effect of noise on communication

interference. For example, according to Berglund and Hassmen

(1996), noise that has a similar frequency to speech will mask it better

than noise at other frequencies, especially higher frequencies, since

lower frequency noise is capable of an "upward spread" (p. 2994) that

is rather effective at masking speech.

Miller (1979a) discusses several other factors affecting noise-induced

speech interference. For example, communication that involves a

higher ratio of speech intensity to noise intensity is more likely to be

understood.

In addition, speech content is also important, since a person that is

trying to convey personal information is less likely to raise his or her

voice to compensate for background noise.

As a result, personal information is less likely to be understood. This

also relates to another influencing factor, culture, which governs how

close two people can be to each other.

Since two people who are close together have a higher speech to noise

intensity ratio than two people who are farther apart, people in

cultures that emphasize personal space are more likely to encounter

communication difficulties in noisy situations.

Another factor influencing communication interference is the age of the

people involved. Specifically, because children have poorer articulation

skills than adults, "their lack of vocabulary or different concepts of the

rules of language may render speech unintelligible when some of the

cues in the speech stream are lost" (Miller, 1979a, p. 125). Thus,

noisy conditions are more likely to interfere with the speech of children

than with that of adults.

Additionally, the ability to understand partially masked or distorted

speech appears to begin deteriorating at around the age of 30. Thus,

"the older the listener, the lower the background noise must be for

practical or satisfactory communication" (p. 125).

Spatial factors also contribute to communication interference, in that

noises that are produced in areas containing highly reverberant

materials become less localized, resulting in greater interference with

communication.

Further, situational factors are also important in their influence on

message predictability and on the availability of non-verbal cues.

That is, predictable messages can often be understood despite highly

noisy backgrounds, such as the snap count of an NFL quarterback in a

noisy stadium, whereas less predictable messages are more poorly

understood, such as speech about unexpected situations that firemen

encounter during a fire.

Though forms of non-verbal communication such as lip-reading or

bodily gestures are often utilized to compensate for such noisy

environments, these again are more efficient in conveying predictable

information, and may not be very useful regarding unexpected events.

Further, some situations preclude the use of such forms of

communication, such as situations often encountered by firemen in

which their visibility is limited due to smoke and as a result lip-reading

and gesturing are useless. (Miller, 1979a)

Noise can obviously be very hazardous, in that it can preclude the

conveyance of vital life-saving information. However, it is the more

benign, everyday conversation that is more often what is disrupted by

noise.

This is not to say, though, that such disruption is not damaging. On

the contrary, everyday conversation disruptions can lead to increased

annoyance and anxiety, and as result may indirectly contribute to

physiological complications such as the non-auditory physiological

effects discussed previously.

Noise Pollution Control

1. Protection of the recipient

Single-use earplugs :

Made of waxed cotton, foam, silicone rubber or fibreglass wool.

When properly inserted, they work as well as most moulded earplugs.

Moulded earplugs :

Must be individually fitted by a professional and can be disposable or reusable.

Reusable plugs should be cleaned after each use.

Earmuffs :

Require a perfect seal around the ear.

Better attenuation of noise.

Glasses, facial hair, long hair or facial movements such as chewing may reduce the

protective value of earmuffs.

By arranging noise sensitive uses such as bedrooms facing away from the noise

sources, the impact of noise on the receiver can be reduced

While acoustic insulation by good glazing can cut down noise, its application for

residential buildings practically deprives the receiver of an "open-window" life style

and requires the provision of air-conditioning due to the warm and humid climate

2. Increasing Path

Interrupting the path of sound can reduce sound exposure.

An obvious way of reducing noise is to separate the sources of noise from noise

sensitive uses.

This is however often not practical in a compact and high-rise city to rely only on

distance attenuation to cut down the noise such as in the case of tackling road traffic

noise.

Additional attenuation, which can be provided through screening by natural

landscape (such as earth bunds), structures of noise tolerant uses (such as carpark,

commercial blocks or acoustic-insulated office buildings), purposely built podium

decking, noise barriers or enclosures are often employed.

Proper land use planning to avoid busy highways cutting across residential

developments or coming too close to sensitive uses; locating noise tolerant uses to

screen noise sensitive developments, and a combination of the different noise

attenuation means can often pre-empt noise problems at the design stage.

Options to avoid or minimize noise, say, through adopting alternative transport such

as railway, pedestrian link, cycling path, underground roads can also be considered

at the early planning stage.

Over large distances (such as those greater than 300 meters) sound can be bent

over by wind or reflected back towards ground by temperature inversions thereby

reducing the attenuating effects.

3. Noise Barrier

A noise barrier or acoustic shield reduces noise by interrupting the propagation of

sound waves. With proper design and selection of material for the noise barrier or

acoustic shield, noise reaching a noise sensitive receiver would be primarily through

diffraction over the top of the barrier and around its ends.

The acoustical "shadow zone" created behind the barrier is where noise levels are

substantially lowered.

To function well, the barrier must prevent the line-of-sight between the noise source

and the receiver.

Effective noise barriers can reduce noise levels by as much as 20 dB(A).

The most common type of path control is a noise barrier.

Noise barriers that block the direct path of the sound reduce the sound exposure to

that resulting from refraction by the barrier and the sound that travels over the top

of the barrier.

Properly designed noise barriers can offer reductions in sound level of up to 20-25

dB, although a 10 dB reduction may be more likely.

The amount of sound reduction is typically proportional to the size of the barrier,

both height and length.

Noise barriers offer the greatest reduction when they are placed close to either the

source or the receiver (the receiver is the person, residence, etc.).

The closer the barrier is to the source, the greater the effective height of the barrier.

Barriers that are closer to the receiver provide abatement by creating a shadow

zone, which typically is only effective for a limited area.

Barriers are least effective when placed in the middle of the source and receiver.

Barriers also lose effectiveness with increasing distance between the source and

receiver, particularly when the barrier is neither close to the source or the receiver.

4. Sources Control

Reducing the source sound emissions results in the most desirable effect; lower

sound levels for everyone without those who are impacted having to provide

mitigation.

Source control can sometimes be the cheapest form of noise reduction since lower

source emissions may preempt alternative mitigation efforts at many other

locations.

Noise control engineering can typically reduce source sound emissions, particularly,

when it is included into the equipment design or prior to installation.

It is typically more difficult to retrofit noise reductions on existing equipment.

Notably, some equipment or operations can not accommodate any or more noise

reduction technology and other methods of noise control must be considered.