pollution

1. Chapter 14 – Noise Pollution and Control
Hwk#7 review questions – pp.472-473 #6,8,15,19
practice prob. – p.474 -#2,7,9,15
•Noise – is an undesirable and unwanted sound,
and noise is a form of waste energy.
[Note: Not all sound is noise]
•Sound Waves - Is the form of transport for sound
and it cannot be transmitted in a vacuum due to a
lack of medium to carry the vibration.

2. Chapter 14 – Noise Pollution and Control
• Wave Lengths-distance between pressure peaks
•Frequency - The number of wavelengths that
appear to pass a fixed point in 1 second. [cps or Hz]
•Amplitude-heights of the peak which represents
the pressure intensity and is related to the volume
or loudness.
•Cycle - is a single wave length
http://www.fi.edu/fellows/fellow2/apr99/soun
dvib.html

3. Chapter 14 – Noise Pollution and Control
• Speed of Sound- 1500 m/s in water and 5000 m/s
in steel, 340 m/s in air (1100 ft/s).
The human ear can detect sounds in the
frequency range of about 20 to 20,000 Hz.
(The average is 200 - 10,000 Hz)
x f
where, v= speed of sound, m/s or ft/s
= wavelength, m/cycle or ft./cycle
f = frequency, Hz or cps
v 
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4. Chapter 14 – Noise Pollution and Control
• microbars- 1 millionth of a bar, where a bar is
equal to 100 kPa or 14.7 psi (atmospheric pressure
at sea level)
The reference pressure generally used for Po is
the hearing threshold or lowest audible sound
pressure of .0002 microbars. (1000 microbars
is the highest sound pressure w/o pain)
0
0
P
SPL = 20 X log ( )
P
where, SPL= sound pressure level, dB
P= rms sound pressure, bar
P = reference pressure, bar
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5. Chapter 14 – Noise Pollution and Control
• decibel scale (dB) - a ratio of two pressures
(Note : 10,000 microbars can cause immediate
physical damage.)
•Sound Pressure Level - expresses the magnitude
of volume or a sound (dB)
[Refer to p.461 in text fig. 14.3]
Note: The avg. person will perceive a high-pitch
sound to be louder than a low pitch sound with
the same SPL. (see fig. 14.5 under sound-level
measurements in phons)
http://www.jimprice.com/prosound/db.htm

6. Chapter 14 – Noise Pollution and Control
• Sound Intensity (W/m2) - is proportional to the
square of the root mean square (rms) value of a
sound pressure or SPL
(Note :for every 10 dB increase in SPL, there is a
10 fold increase in sound intensity.)
•Frequency Weighting Networks- noise is broken
down to bands of low-medium-high frequency.
“A-weighted” network filters out low and high
frequency where human ears is less efficient.
[dBA is a.k.a A-weighted decibels]
[Refer to p.464 in text fig. 14.3]
Sound Level (SL)- Sound Level measurement over
a period of time. i.e. L90=75 dBA means 90% of
the time sound level exceeeded 75 dBA.

7. Chapter 14 – Noise Pollution and Control
• Sound Exposure Level (SEL) - provides a basis
for computing noise events of variable durations
which matches a person’s impression of noise. It
is standardized to 1 sec. (Note: refer to figure
14.7, p. 465)
•Equivalent Sound Level (Leq)- is is the average
or constant SPL over the period of interest. [i.e.
Leq(8) is the average for an 8 hr. period.]
[Refer to p.464 in text fig. 14.3]
•Day - Night Sound Level (DNL)- Leq(24) with a
10-dBA penalty for night time which is more
annoying. see fig. 14.8
[Note: Noise can cause damage to our irritability,
anxiety, stress and other emotional symptoms.]
Temporary Threshold Shift (TTS)- Temporary
hearing loss (approx. 1 month)
Noise -induced permanent threshold shift
(NIPTS) - loss of hearing with no chance of
recovery

8. Chapter 14 – Noise Pollution and Control
• less than 80 dBA -no hearing loss
•80 to 130 dBA - TTS hearing loss is noticeable
•50 % of people exposed to 95-dBA will
experience NIPTS (permanent hearing loss)
•150 dBA or greater- can physically rupture the
human eardrum.
(Note: 1 hr. of 100 dBA can produce TTS whereas
8 hours of 95 dBA over 10 years may cause NIPTS)
B
B
A
D
10X log
D
A
SL S
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