| • Sound is a longitudinal
wave transmitted through a gas, liquid, or solid.
• A sound wave is an oscillation
in the pressure of the medium. |
 |
• A sound wave is composed of
compressed regions of air (compressions) and lower density regions (rarefractions).
• The velocity of sound in air
at sea level at room temperature (20oC) is 343 m/s.
• The velocity of sound equals
its wavelength times the frequency.
• The velocity of sound depends
upon the medium.
• Sound travels faster in
denser medium.
• The Doppler
shift is the change in frequency of sound caused by motion of the source
or the detector.
• The frequency of a sound wave
is called its pitch.
• Two notes that differ by
one octave have pitches in the ratio of two to one.
• The relative intensity
of sound is measured on a scale of decibels (dB). examples
• The decibel scale is logarithmic
... the volume doubles for every 10 dB increase.
• Sound intensity is equal
to the power divided by the area (4*pi*r2).
• The ear and brain perceive
the amplitude as loudness. |
 |
 |
• Humans can hear sound waves
between 20 and 20,000 Hz.
• Sound waves below 20 Hz
are called infrasonic.
• Sound waves above 20,000
Hz are called ultrasonic.
| • Ultrasonic sound waves
can be used for imaging (similar to radar). |
 |
• Sound is produced by vibrating
objects.
• An air column can resonate
with a sound source, increasing the loudness of the source.
• A forced vibration at the
natural frequency
produces resonance.
|
|
• Sound detectors convert sound
energy into a different form of energy.
• Two waves with almost the
same frequency interfere to produce a beat note.
• Most sounds consist of
waves with more than one frequency.
• The fundamental frequency
determines pitch.
• The quality of sound (timbre)
depends on the humber and intensity of harmonics.
• The shape of the throat
and mouth cavity determine the vowel sounds produced by the human voice.
Decibel
Levels
Source
Intensity
Threshold of Hearing
0 dB
Rustling Leaves
10 dB
Whisper
20 dB
Normal Conversation
60 dB
Busy Street Traffic
70 dB
Vacuum Cleaner
80 dB
Large Orchestra
98 dB
Walkman at Maximum Level
100 dB
Front Rows of Rock Concert
110 dB
Threshold of Pain
130 dB
Military Jet Takeoff
140 dB
Instant Perforation of
Eardrum 160 dB |
