2. Noise & Music
What is noise?
Is a combination of sounds that has no specificIs a combination of sounds that has no specific
pitch. If the wave form is analyzed, it is foundpitch. If the wave form is analyzed, it is found
that there isthat there is no repeating wave form.repeating wave form.
What is music?
Is a combination of sounds where eachIs a combination of sounds where each
frequency is a whole number multiple of thefrequency is a whole number multiple of the
lowest natural frequency. We have previouslylowest natural frequency. We have previously
referred to these sounds as harmonics (1referred to these sounds as harmonics (1stst
,,
22ndnd
, …)., …).
3. Sound Intensity & Loudness
Loudness is the easiest to define as it is subjective.is the easiest to define as it is subjective.
What is loud to one person may not be loud to anotherWhat is loud to one person may not be loud to another
person.person.
Sound Intensity, however, is measurable. It is defined, however, is measurable. It is defined
asas the amount of sound energy (J) reaching 1 m2
in 1 s..
We know that a J/s is a watt, and since the quantity ofWe know that a J/s is a watt, and since the quantity of
“power” is very small the unit used is the picowatt (pW),“power” is very small the unit used is the picowatt (pW),
wherewhere 1pW = 1x10-12
W. Applying the 1 m. Applying the 1 m22
area thearea the
final unit of measure is thefinal unit of measure is the pW/m2
.
Humans experience sound levels from 1 to 10Humans experience sound levels from 1 to 101010
pW/mpW/m22
..
Due to this large range, a logarithmic scale, to base 10,Due to this large range, a logarithmic scale, to base 10,
was adopted. The new unit is called thewas adopted. The new unit is called the bel (B), afterafter
Graham Bell. So: 0 B = 1 pW/mGraham Bell. So: 0 B = 1 pW/m22
, (Since, 0 B = 1, (Since, 0 B = 1
pW/mpW/m22
) and 10 B = 10) and 10 B = 101010
pW/mpW/m22
..
Humans tend to hear differences in intensity of 0.10 B,Humans tend to hear differences in intensity of 0.10 B,
or about 1.3 pW/mor about 1.3 pW/m22
. For this reason the unit commonly. For this reason the unit commonly
used is theused is the decibel (dB) where 1B = 10 dB.where 1B = 10 dB.
4. Examples of Sound Intensity
A subway generates about 90 dB in noise anA subway generates about 90 dB in noise an
average conversation is about 50 dB, pneumaticaverage conversation is about 50 dB, pneumatic
construction drill is about 110 dB and immediateconstruction drill is about 110 dB and immediate
pain occurs at about 120 dB. Rustling leavespain occurs at about 120 dB. Rustling leaves
measure about 10 dB. Even at 90 dB, hearingmeasure about 10 dB. Even at 90 dB, hearing
damage can result with continued exposure.damage can result with continued exposure.
Example: Determine the sound intensity in dBDetermine the sound intensity in dB
for 123 pW/mfor 123 pW/m22
..
Answer: Log(123) = 2.09 (B), so 2.09 B = 20.9 dB.Log(123) = 2.09 (B), so 2.09 B = 20.9 dB.
5. Echolocation
An echo is just a reflection of sound waves.An echo is just a reflection of sound waves.
Bats and dolphins use the reflection ofBats and dolphins use the reflection of
sound waves to determine the location ofsound waves to determine the location of
an object.an object.
Boats and submarines useBoats and submarines use sonar (sound(sound
navigation and ranging) to determinenavigation and ranging) to determine
distances underwater by sending out adistances underwater by sending out a
short burst of sound (“ping”). The time thatshort burst of sound (“ping”). The time that
it takes to reach the target and then comeit takes to reach the target and then come
back is measured. Since the speed ofback is measured. Since the speed of
sound in water is known, the distance (sound in water is known, the distance (d))
can be calculated. (Multiplycan be calculated. (Multiply d byby ½ -why?)½ -why?)
6. Human Hearing
Literature often tells us that humans having aLiterature often tells us that humans having a
range of hearing from 20 – 20,000 Hz. As werange of hearing from 20 – 20,000 Hz. As we
age, we tend to lose much of the higherage, we tend to lose much of the higher
frequency range of our hearing. You can testfrequency range of our hearing. You can test
your hearing range by using the YouTube videoyour hearing range by using the YouTube video
linklink or downloading free NCH Tone generator or.downloading free NCH Tone generator or.
http://www.youtube.com/watch?v=9g0yThhJcxYhttp://www.youtube.com/watch?v=9g0yThhJcxY
http://www.nch.com.au/tonegen/index.html?http://www.nch.com.au/tonegen/index.html?
gclid=CMDVqrfS8qoCFUUBQAodIHY5OAgclid=CMDVqrfS8qoCFUUBQAodIHY5OA
7. Practice Questions
From Nelson TB:
Page 397 #5, 10 Page 474 # 2, 3Page 397 #5, 10 Page 474 # 2, 3 Page 489 # 14Page 489 # 14
Page 491 #14Page 491 #14 Page 493 # 47Page 493 # 47 Page 495 # 81Page 495 # 81
Calculate the following:
A.) Express 300 pW/mA.) Express 300 pW/m22
in both B and dB.in both B and dB.
(Ans. 2.48 B, 24.8 dB)
B.) Express 2.5 dB in pW/mB.) Express 2.5 dB in pW/m22
(Ans 1.8 pW/m2
)
Questions from the McGraw-Hill TB
1.1. The human ear is just able to distinguish soundsThe human ear is just able to distinguish sounds
that arethat are 0.10 s apart. How far from a wall must aapart. How far from a wall must a
person stand to just hear an echo? (useperson stand to just hear an echo? (use
v=343m/s)v=343m/s) (Ans. 17m)
8. 2.2. A neighbour explains that the old wellA neighbour explains that the old well
behind his house isbehind his house is 300 m deep. Youdeep. You
decide to see for yourself. You drop adecide to see for yourself. You drop a
stone from rest and measure the timestone from rest and measure the time
interval until you hear the splash of theinterval until you hear the splash of the
stone striking the water. You find it to bestone striking the water. You find it to be
6.0 s. You determine that the speed of. You determine that the speed of
sound in air to be 343 m/s. How deep issound in air to be 343 m/s. How deep is
the well? (the well? (Ans 152 m))
