EXPERIMENT 3:
Title: Title: TRAFFIC TRAFFIC NOISE NOISE MEASUR MEASUREME EMENT NT
Objectives:
After conducting this experiment student should be able to:
1.
Unde Unders rsta tand nd the the fun funda dame ment ntal al conc concep eptt in in noi noise se poll pollut utio ion n
2.
Unde Unders rsta tand nd the the tec techn hniq ique ue use used d in in traf traffi ficc nois noisee mea measu sure reme ment nt
3.
Inve Invest stig igat atee some some of of the the fac facto tors rs that that can can lea lead d to noi noise se poll pollut utio ion n
Introduction:
The word "noise" is derived from the Latin word "nausea," meaning seasickness. Noise is among the most pervasive pollutants today. Noise can be defined as any sound independent of loudness that can produce an undesired physiological or psychological effect in an individual and that may interfere with the social ends of an individual group. Noise from road traffic, jet planes, jet skis, garbage trucks, construction equipment, manufacturing processes, lawn mowers, leaf blowers, and boom boxes, to name a few, are among the audible litter that are routinely broadcast into the air. Noise pollution does negatively affect us and the environment. In humans, aside from annoyance, it's been shown that exposure to moderately high levels of noise for an eight hour period can increase blood pressure and cause other cardiac issues - even if the person is not particularly consciously disturbed. Noise pollution can also cause gastric problems. Sometimes a person doesn't even realize their body is stressed by b y noise until the noise is no longer present they just feel a sudden sense of relief.
Exposure to excessively loud noise over long periods can also lead to partial deafness. Approximately 10 percent of people living in industrialized areas have substantial hearing loss and youngsters in the USA have an impaired hearing rate 250% higher than their parents and grandparents. Many environmental noise measurements are made for planning purposes, to check noise levels against local noise ordinances or to investigate noise nuisance complaints between neighbors. Results are usually taken on property boundaries or at specific positions laid down in the appropriate measurement protocols (or ordinances). When nuisance complaints are being investigated it may be necessary to make measurements inside houses or apartments to assess the noise levels between party walls. Different noise limits may apply at certain times of the day and night to reflect people's sensitivity to disturbances during the day. Simple sound level meters such as the CEL-254 or CEL-320S can be used.
Sound is produced by the vibration of bodies or air molecules and is transmitted as a longitudinal wave motion. It is, therefore, a form of mechanical energy and is measured in energy-related units. The sound output of a source is measured in watts and the intensity of sound at a point in space is defined by the rate of energy flow per unit area, measured in watts per ms. Intensity is proportional to the mean square of the sound pressure and, as the range of this variable is so wide, it is usual to express its value in decibels (dB)a. Because the effects of noise depend strongly upon frequency of sound pressure oscillation, spectrum analysis is important in noise measurement.
Sound exposure level - in decibel - is not much used in industrial noise measurement. Instead, the time-averaged value is used. This is the time average sound level or as it is usually called the 'equivalent continuous sound level' has the formal symbol L AT . These mainly, follow the formal ISO acoustic definitions qv. However, for mainly historical reasons, L AT is commonly referred to as Leq. Formally, L AT is 20 times the base 10 logarithm of the ratio of a root-meansquare A-weighted sound pressure during a stated time interval to the reference sound pressure and there is no time constant involved. To measure L AT an integrating-averaging meter is needed;
this in concept takes the sound exposure, divides it by time and then takes the logarithm of the result.
Leq is the constant noise level that would result in the same total sound energy being produced over a given period. It can be measured in either A, C or Z (Linear) modes. Leq can be described mathematically by the following equation:
Where: •
Leq is the equivalent continuous linear weighted sound pressure level re 20µPa, determined over a measured time interval Tm (secs)
•
P(t) is the instantaneous sound pressure of the sound signal
•
P0 is the reference sound pressure of 20µPa
When the instantaneous A-weighted sound pressure (PA) of the sound signal is introduced the the equivalent continuous A-weighted sound pressure level determined over time interval Tm is as follows:
In practise when measuring noise it is possible to take Leq readings, with your instrument, of short duration, ie <5 minutes, providing all variations of noise emissions are covered. If the measured environment changes greatly then the longer the Leq measurement is taken the more accurate the measurement. Adding Leq values requires taking an anti-log of each value. The addition can be performed as shown:
Method:
1.
The test site
The appropriate test site was choosed
The characteristic of the test site were: test site must substantially level, the surface dry and its texture should • be such that is does not cause excessive tyre noise Within a radius of 50m around the center of the track, the space shall • be free of large reflecting object. The background noise shall be at least 10dB below that produced by • the vehicle under test.
The microphone should be set up at height 1.2m above the ground which is the height ear level of an average human height.
The distance from microphone to reference line on test track shall be 7.5m as shown in the figure below:
Figure: Measurement set-up
Our site is at Main Gate of UPSI (in front Poliklinik Syifa)
2.
The sound level meter
The sound level meter was set up as follows: •
Set response to Fast (F) so that it can measure not too rapidly fluctuating noise levels.
•
Set function to A weighting where very low frequencies are filters quite severely compared to B and C weighting.
•
Select high range where this range covers sound levels between 60 and 120dBA.
At test site take sound level was measurement at both sides of the road in each five minutes interval within one hour. The result was record.
At the same time the traffic composition was record and flow at each side of the road. Traffic composition may include car, van, light truck<3.5 ton, truck or lorry > 3.5 ton, buses and motorcycles.
A graph which consists of time (min) against sound level (dBA) was plotted and sound pressure average (L p) and equivalent continuous equal energy level (Leq) were calculated based on the given equations.
RESULT
Instrumental site: Main gate of UPSI ( In front the Poliklinik Syifa)
dBA Reading Time, t (min)
5 10 15 20 25 30 35 40 45 50 55 60
dBA East Entrance UPSI ( noise ) 67.0 71.6 66.6 64.3 71.3 68.7 71.1 70.1 65.9 70.0 68.0 66.4
Traffic Composition Time, t (min) 5 10 15 20 25 30 35 40 45 50 55 60
car 15 26 24 13 11 16 25 5 19 7 15 9
van 2 1 2 1 3 -
Type of Vehicles motorcycle 25 45 20 18 19 23 40 16 23 18 17 16
lorry 1 -
jeep 1 1 1 -
CALCULATION
i)
Lp = 20 log [ 1 / N X ∑ [ log-1 ( Lj / 20 ) ] ] Lp = 20 log [ 1 / 12 X ∑ [ log -1 ( 67.0 / 20 ) + log-1 ( 71.6 / 20 ) + log-1 (66.6/20 ) +log1
( 64.3 / 20 ) + log -1 ( 71.3 / 20 ) + log -1 ( 71.1/ 20 ) + log -1 ( 70.1 / 20 ) + log -1
( 65.9 / 20 ) + log-1 ( 70.0 / 20 ) + log-1 ( 68.0 / 20 ) + log-1 ( 66.4 / 20 ) + log-1 ( 68.7/ 20 )
= 68.72 dB
ii)
Leq = 10 log [ ∑ [ 10 Li/10 x t i] ], where t i = t / 60 Leq = 10 log [ ∑ [ ( 10 64.3/10
67.0/10
x 5/60) + ( 10 71.6/10 x 10/60) + ( 10 66.6/10 x 15/60) + ( 10
x 20/60) + ( 10 71.3/10 x 25/60) + ( 10 68.7/10 x 30/60) + ( 10 71.1/10 x 35/60)
+ ( 10 70.1/10 x 40/60) + ( 10 55/60) +( 10 66.4/10 x 60/60)
= 76.98 dB.
65.9/10
x 45/60) + ( 10 70.0/10 x 50/60) +( 10 68.0/10 x
DISCUSSION
•
Noise pollution (or environmental noise) is displeasing human-, animal- or machinecreated sound that disrupts the activity or balance of human or animal life. A common form of noise pollution is from transportation, principally motor vehicles.
•
Noise health effects are both health and behavioural in nature. The unwanted sound is called noise. This unwanted sound 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.
•
High noise levels can contribute to cardiovascular effects 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.
•
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.
•
An impact of noise on animal life is the reduction of usable habitat that noisy areas may cause, which in the case of endangered species may be part of the path to extinction. One
of the best known cases of damage caused by noise pollution is the death of certain species of beached whales, brought on by the loud sound of military sonar.
•
Sound level meters measure sound pressure level and are commonly used in noise pollution studies for the quantification of almost any noise, but especially for industrial, environmental and aircraft noise. However, the reading given by a sound level meter does not correlate well to human-perceived loudness; for this a loudness meter is needed.
•
The standard sound level meter is more correctly called an exponentially averaging sound level meter as the AC signal from the microphone is converted to DC by a root-meansquare (RMS) circuit and thus it must have a time-constant of integration; today referred to as time-weighting.
•
The output of the RMS circuit is linear in voltage and is passed through a logarithmic circuit to give readout linear in decibels (dB). This is 20 times the base 10 logarithm of the ratio of a given root-mean-square sound pressure to the reference sound pressure. Root-mean-square sound pressure being obtained with a standard frequency weighting and standard time weighting.
•
The frequency range of human hearing is generally considered as 20 – 20,000 Hz. The upper range varies greatly among individuals and decreases with age and noise exposure. The amplitude of our sensation ranges from the threshold of hearing (~0 dB) to thresholds of discomfort and pain (above 140 dB).
•
In our experiment on this sound pollution at UPSI Pintu Utama road, equivalent continuous sound level, Leq measured is 68.72 dB. This level is safe for human being and animals.
•
Noise pollution can be reduce by raise awareness about noise pollution such create, collect, and distribute information and resources regarding noise pollution and distribute its to public. Beside that, we can strengthen laws, governmental efforts to control noise pollution and also assist activists working against noise pollution.
CONCLUSION
Equivalent continuous sound level, Leq measured in our noise pollution experiment is 68.72 dB.
REFERENCESS
Anonymous. NPC Noise Pollution Clearinghouse.
from http://www.nonoise.org/index.htm.
Access on March 22, 2009. Anonymous. Noise Pollution.
from http://en.wikipedia.org/wiki/Noise_pollution. Access on
March 22, 2009. Anonymous. Sound Level Meter.
from http://en.wikipedia.org/wiki/ Sound_Level_Meter.
Access on March 22, 2009. Anynamous. Environmental Noise Measurements. Access from http://www.casellausa.com/en/cel/environm.htm. Access on March 22, 2009.
