ch9: Noise pollution Flashcards
The nature of sound
- Sound, a manifestation of vibration, travels in wave patterns through solids, liquids and gases.
- The waves, caused by vibration of the molecules, follow sine functions, typified by the amplitude and wavelength (or frequency)
- Sound waves of equal amplitude with increasing frequency from top to bottom
People generally hear sounds between
the “threshold of hearing” and the “threshold of pain”
People generally hear sounds between the “threshold of hearing” and the “threshold of pain” In terms of pressure, this is
20 upa - 100 pa
People generally hear sounds between the “threshold of hearing” and the “threshold of pain” In terms of pressure, this is 20 μPa – 100 Pa
…………………………. was developed from this fact and ……………………………..
the decibel scale
makes numbers more manageable
The decibel scale generally ranges from
approximately 0 to 130
the sound pressure of the faintest sound that a normal healthy individul can hear is about
0.00002 pa
the sound pressure produced by a saturn rocket at liftoff is
greater than 200 pa
the sound pressure produced by a saturn rocket at liftoff is greater then 200 pa. even in scientific notation this is
an astronomical range of numbers
the sound pressure produced by a saturn rocket at liftoff is greater then 200 pa. even in scientific notation this is an astronomical range of numbers. to cope with this problem
a scale based on the logarithm of the ratios of the measured quantities is used.
the sound pressure produced by a saturn rocket at liftoff is greater then 200 pa. even in scientific notation this is an astronomical range of numbers. to cope with this problem a scale based on the logarithm of the ratios of the measured quantities is used.
measurements on this scale are called
levels
the sound pressure produced by a saturn rocket at liftoff is greater then 200 pa. even in scientific notation this is an astronomical range of numbers. to cope with this problem a scale based on the logarithm of the ratios of the measured quantities is used. measurements on this scale are called levels.
the unit for these types of measurement scales is
the bel
level, bels:
L=log( Q/Q0)
L=log( Q/Q0) explain the terms
L = levels, bels
Q= measured quantity
Q0= reference quantity
log= logarithm in base 10
bel turns out to be
larger unit so for convenience it is divided into 10 subunits called decibels (dB)
levels in decibels are computed as follows
L=10log Q/Q0
the decible doesnt represent
any physical unit. it indicates that a logarithmic transformation has been performed
W: Sound energy
is a form of energy associated with the vibration of matter.
I: Sound intensity
also known as acoustic intensity is defined as the Energy carried by the sound waves per unit area
If the reference quantity Q0 is specified then
the decibel takes physical significance
for noise measurements the reference power level has been established as
10-12 W
sound power level may be expressed as
Lw = 10 log (w/10-12)
for noise measurements, the reference sound intensity is
10-12 W/m2
sound intensity level
Li = 10 log (I/10-12)
sound measuring instruments measure
Prms
sound pressure level =
the reference pressure has been established as
20 uPa (micropascal)
Humans are less sensitive to
low frequency sound
humans are more sensitive to
high frequency sound
Humans are less sensitive to low frequency sound and more sensitive to high frequency sound. Therefore,
sometimes the dB scale is adjusted to take this into account
sometimes the dB scale is adjusted to take this into account:
- A-weighting (db(A)): adjusts overall scale so it better matches what the human ear would hear
- C-weighting (dB(C)): adjusts scale for loud or low frequency sounds
- B-weighting (dB(B)): adjusts by factors that are “in between” the A-weighted factors and C-weighted factors (rarely used)
human hearing and frequency graph
how sound is measured
pressure
P
usually in pascals
p=1/f
how sound is measured
frequency
f
usually in hertz
how sound is measured
intensity
I
usually W/m2
I=W/A
How sound is measured
bels
L’
derived from logarithmic ratio
L’=log (Q/Q0)
How sound is measured
Decibels
L
derived from bels
L=10*log (Q/Q0)
Implications of the decibel scale:
doubling sound level would mean that the sound will increase by 10*log2 = +3dB Ten times the sound level = 10*log10 = +10dB
Other descriptors of sound
- Equivalent sound level – the level of sound that has the same acoustical energy as does a time-varying sound over a stated time period.
- Percentile sound level – the sound level exceeded “n” percent of the observation time interval.
- Day-night average sound level – the equivalent sound level for a 24-h period that incorporates a decibel penalty during night hours.
Noise” derived from
“nausea,” meaning seasickness
Noise is among the most
pervasive pollutants today
Noise is unavoidable for
many machines
We experience noise in a number of ways
- üenvironmental
- ücause and victim
- generated by others “second-hand”
Noise negatively affects
human health and well-being
The air into which second-hand noise is
emitted and on which it travels is a “commons“, a public good
NOISE POLLUTION
¢Sound that is unwanted or disrupts one’s quality of life is called as noise. When there is lots of noise in the environment, it is termed as noise pollution.
Sound becomes undesirable when it
¢disturbs the normal activities such as working, sleeping, and during conversations.
Sound becomes undesirable when it disturbs the normal activities such as working, sleeping, and during conversations.
It is an underrated environmental problem because
of the fact that we can’t see, smell, or taste it.
World Health Organization stated that (about noise pollution)
Noise must be recognized as a major threat to human well-being
Noise must be recognized as a major threat to human well-being
direct links between noise and health. Also, noise pollution adversely affects the lives of millions of people
Noise pollution can damage
physiological and psychological health.
the health problems related to noise pollution
- High blood pressure,
- stress related illness,
- sleep disruption,
- hearing loss, and
- productivity loss
- memory loss
- severe depression
- panic attacks
Sources of Noise Pollution
- •Transportation systems are the main source of noise pollution in urban areas.
- •Construction of buildings, highways, and streets cause a lot of noise, due to the usage of air compressors, bulldozers, loaders, dump trucks, and pavement breakers.
- •Industrial noise also adds to the already unfavorable state of noise pollution.
- •Loud speakers, plumbing, boilers, generators, air conditioners, fans, and vacuum cleaners add to the existing noise pollution.
Noise contours around an airport calculated using
INM (Integrated Noise Modeling)
Noise contours around an airport calculated using INM (Integrated Noise Modeling) based on
previous noise measurements
Other sources of noise pollution that need to be addressed
- Boat noise, especially jet skis
- Construction noise
- Snow mobiles
- Industry
Solutions for Noise Pollution
- Planting bushes and trees in and around sound generating sources is an effective solution for noise pollution.
- Regular servicing and tuning of automobiles can effectively reduce the noise pollution.
- Buildings can be designed with suitable noise absorbing material for the walls, windows, and ceilings.
- Workers should be provided with equipments such as ear plugs and earmuffs for hearing protection.
- Similar to automobiles, lubrication of the machinery and servicing should be done to minimize noise generation.
- Soundproof doors and windows can be installed to block unwanted noise from outside.
- Regulations should be imposed to restrict the usage of play loudspeakers in crowded areas and public places.
- Factories and industries should be located far from the residential areas.
- Community development or urban management should be done with long-term planning, along with an aim to reduce noise pollution.
- Social awareness programs should be taken up to educate the public about the causes and effects of noise pollution.
Roadway Noise
An example of a “line source” of noise pollution (as opposed to a “point source”)
Level of noise is a function of
- volume,
- type of vehicle, and
- speed
Roadway Noise - Solutions
- • Regulations limit the amount of noise some vehicles can produce
- • Some regulations require vehicles to be properly operated and maintained
- • Despite regulations, the noise levels are usually only reduced by 5 to 10 dBA
Barriers
- •Buffer zones
- •Earth berms/wooden fences/concrete walls
- •Vegetation (if dense enough)
Pavement type
- Certain asphalts, such as those containing rubber or stone, can be less noisy than other pavements.
- However, some studies have shown the reduction in noise is only a few decibels, not enough to be significant.
- More research is needed before pavement type can be an effective noise-reducing technique
air noise solutions
