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Discovery of Sound in the Sea
The Discovery of Sound in the Sea web site will introduce you to the science and uses of Sound in the Sea. There are several major sections on the site such as The Science of Sound in the Sea, People and Sound in the Sea, and Animals and Sound in the Sea. You will find the site's Audio Gallery a fascinating place to visit where you can listen to underwater sounds created by marine animals, human activities, and natural phenomena such as lightning, earthquakes, and rain. Check out the technology gallery and discover a variety of equipment that uses sound to investigate the ocean. Watch video interviews with scientists that study how marine animals produce and hear sounds. Investigate how scientists use underwater acoustics to track ocean currents, identify potential obstacles, and quantify fish distributions. There is also a special section for teachers with resources and classroom activities.
http://www.dosits.org/science/intro.htm
(website developed by the University of Rhode Island) |
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Acoustic
Monitoring Program: Underwater Acoustics Tutorial |
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The
following is a very brief overview of the basic principles of underwater
acoustics.
The tutorial is presented in twelve topics beginning with "What is
Sound?". |
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1.
What is Sound? |
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A
propagating sound wave consists of alternating compressions
and rarefactions which are detected by a receiver as changes
in pressure. Structures in our ears, and also most man-made
receptors, are sensitive to these changes in sound pressure
(Richardson et al.1995, Gordon and Moscrop 1996).
 The basic components of a sound wave are
amplitude, wavelength, and frequency:
The amplitude
of a sound wave is proportional to the maximum distance a vibrating particle
is displaced from rest. Small variations in amplitude produce weak or
quiet sounds, while large variations produce strong or loud sounds. The
wavelength of a wave is the distance between two successive compressions
or the distance the wave travels in one cycle of vibration. The frequency
of a sound wave is the rate of oscillation or vibration of the wave particles
(i.e. the rate amplitude cycles from high to low to high, etc.). Frequency
is measured in cycles/sec or Hertz (Hz). To the human ear,
an increase in frequency is perceived as a higher pitched sound, while
an increase in amplitude is perceived as a louder sound. Below are examples
of sound waves that vary in frequency and amplitude.
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These two waves have the same frequency but different amplitudes.
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These two waves have the same amplitude but different frequencies. |
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Note
that increasing the frequency of a sound in equal steps will lead to perceived
increases in pitch that seem to grow smaller with each step. For example,
click on the sound frequencies below, and you'll see a more noticeable
difference between 200 Hz and 225 Hz than 400 Hz and 425 Hz.
200Hz
225Hz 250Hz 275Hz 300Hz 325Hz 350Hz 375Hz 400Hz 425Hz 450Hz 475Hz
Entire
Series
Humans generally
hear sound waves whose frequencies are between 20 and 20,000 Hz. Below
20 Hz, sounds are referred to as infrasonic, and above 20,000 Hz as ultrasonic.
infrasonic
(about 20 Hz) < human hearing < ultrasonic (about 20,000 Hz)
 We
know a great deal about human hearing, but what about the hearing of large
whales? Currently, we do not have detailed audiograms for the larger,
baleen whales (note: we do have information on the hearing of smaller
porpoises and dolphins from research with captive animals). Instead,
we assume whales can hear the range of sounds they produce. The
figure above compares human vocalizations with the sounds baleen whales
are known to produce.
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