Kristin
Lozeau
Communications
141
Semester
Project
April
24, 2001
Modern
society has greatly benefited from underwater acoustic technologies and from
research on the sound of water for therapy.
Underwater acoustic techniques are used to monitor the climate, research
ocean wildlife, detect submarine activity and for commercial entertainment
purposes. Research has shown that the
sound of water invokes many positive feelings and emotions in the listener. The sounds can be peaceful, relaxing,
energizing and can even be used as a kind of therapy. There are several products in the consumer market that
incorporate the sound of water and are used to improve physical and
psychological conditions. I am going to
focus on the science of sound moving through water and how humans are able to
hear underwater. I will also look at
the actual sound that water creates, along with the emotions that it invokes in
the listener.
When
a sound wave moves through water there is a net flow of energy in the direction
the wave travels. Sound underwater
travels at a speed between 4750 and 5150 feet per second, which is nearly five
times faster than the speed of sound in air.
The speed in water depends on factors such as temperature, salinity and
the pressure of the water. Sound
travels faster when the water molecules are at a higher temperature, in
example, the speed increases seven feet per second when the temperature
increases by one degree Fahrenheit. It
also travels faster because water is a much denser medium than air. The water molecules are much closer together
than air molecules, giving sound a shorter traveling time (Nova). In the ocean, the speed of sound in water is
influenced more by temperature in the upper layers and influenced more by
pressure in the lower layers (Beyond).
Many
factors affect how far sound travels underwater and how long it lasts before
dying out. Particles of seawater can
reflect, scatter or absorb certain frequencies of sound, which has an affect on
how far sound travels (Beyond). Seawater
absorbs thirty times the amount of sound as can be absorbed by distilled water
with chemicals. Researchers have
discovered that low frequency sounds that pass over small particles travel
greater distances without loss through absorption or scattering (Beyond). The distance at which a sound can be heard
also depends on its intensity and tonality.
“Underwater
acoustics” is the science of using sound waves underwater as a method of
navigating, communicating and detection (Underwater). It was once thought that the ocean was silent, but now we know
that it is full of sound, both anthropogenic and natural. Anthropogenic sounds underwater, which are
made by humans, are caused by shipping boats, submarine sonar and seismic
testing equipment. Natural sounds underwater
can originate where the earth’s tectonic plates collide, or be caused by
underwater landslides, icebergs breaking off, earthquakes, heavy rains on the
water surface and animals. Ocean
animals makes noises while swimming, searching for food, sending defense or
attack warning signals, sending a mating call, when they are frightened and
when they communicate with each other.
Human ears are unable to pick up the frequencies of many of these
underwater animal sounds because our hearing threshold is only between 20 and
20,000 Hz. Anthropogenic sounds, such
as submarine sonar can be dangerous to divers’ hearing.
Humans
perceive sound under water by bone conductivity, which is the vibration of the
bones of the skull (Physics). Sound
waves enter the ear and strike the tympanic membrane or eardrum, which vibrates
the bones of the middle ear. The
vibrations are transmitted to the fluid in the inner ear and then vibrate the
hair cells that line it. The hair cells
are connected by neurons to the auditory nerve, which transmits the signal to
the brain. The number of hair cells
stimulated determines the volume of the sound and the distribution pattern of
stimulated cells determines the pitch of the sound.
It
is proven that bone conductivity is weaker than air conductivity by forty
percent, therefore we are already at a disadvantage when hearing sounds
underwater. Air conductivity underwater
disappears because the outer audial opening is filled with water and the eardrum
cannot vibrate normally (Physics). One
disadvantage to hearing underwater is that sound seems to be coming from all
directions, making it difficult to find the origin. In order to perceive sounds you have to be at least partially
immersed in the water. Even if you are
standing in water up to your knees, you can hear sounds that you previously
could not hear (Physics). Sounds
underwater are usually inaudible above the surface and sounds above are not
usually heard underwater.
One way to create an acoustic signal
underwater is to create an electronic signal and convert it into mechanical
energy (ITC-About). A transducer is a
device that converts one form of energy to another and has the capability of
transmitting and receiving sound. The
medium of water allows for good transmission of acoustic energy leading to many
underwater applications for transducers.
Electroacoustic transducers are used for sonar detection, underwater
depth measurement and underwater communications (ITC-About).
Environmentalists
fear that human-created underwater noise poses a threat to marine life and to
divers. There are no limits for noise
exposure underwater like there is in air.
The noise pollution comes from large-scale shipping, boat propellers,
oil exploration equipment, military sonar devices and seismic testing. In dark ocean waters, mammals such as
dolphins and whales use their sense of hearing to find food, find mates and to
keep their young safe (abcnews). Marine
mammals use the system of echolocation to orient themselves with their
surroundings, navigate through the water and to find food. This noise pollution interferes with the way
marine animals communicate and it disturbs their migration and breeding
patterns.
The
discovery of new technologies has made it possible to better hear sound underwater
for entertainment, diving, and athletic purposes, through the use of an
underwater speaker system. Underwater
speakers for a backyard swimming pool can easily be purchased from a number of
aquatic companies. Ocean Engineering
Enterprises is the official sound system supplier for USA Synchro and the U.S.
National Synchronized Swimming Teams.
The company manufactures underwater speakers, diver recall systems,
hydrophones, and synchronized swimming sound systems. One particular product offered is the Oceanears 2000 Synchronized
Swimming Sound System with a dual cassette deck and CD player. Another product that is offered is the
Oceanears SP-7 Swimming Pool Loudspeaker.
It works by replacing an existing light bulb with a “sonic-bulb”.
Researchers
use acoustic techniques to monitor climate, such as using sound to measure
rainfall over the ocean. Since 1985,
they have used hydrophones to listen to rainfall across the ocean, acoustically
measuring the rate and type of rain (Probing).
A hydrophone functions by picking up acoustic energy underwater and
converting it into electrical energy.
The monitoring of rainfall patterns will contribute to the understanding
of major climate and weather changes (Probing).
Underwater
speakers are necessary for the Olympic sport of synchronized swimming. The speaker is generally hung near the
middle of the competition area and approximately one-meter below the water
surface. Synchronized swimmers are
judged partially on Artistic Impression, which means that choreography and how
they interpret their music are key elements.
In order for the athletes to time their movements accurately, it is
critical for them to clearly hear their music underwater.
As
a competitive swimmer, I listen to the sounds of water everyday. I hear the splash when I dive into the pool,
the water being forced aside as I streamline through it, and the “pop” as my
head breaks the surface for air. I also
hear the rhythmic sound of my stroke as I am swimming, the water dripping off
my face when I finish and the gurgling of the gutter system when I stop at the
wall. These sounds are soothing to me
and provide a feeling of peacefulness.
The water gives me some time to myself and it enables me to tune out
everyone and everything around me.
Koury
Natatorium on the UNC campus is lucky enough to have underwater speakers. When I am swimming on the surface it is
difficult to hear the music because one ear is always outside the water when I
am taking a breath. Also, the splash of
the water around my head and any deck noise such as yells or whistles, drowns
out the music. Occasionally, my group
will practice underwater pull-outs for breaststroke and I am able hear the
music more clearly. I enjoy the
underwater speaker system because it provides a nice distraction and takes my
focus away from how badly I need oxygen.
There
are several products in the consumer market that incorporate the sound of water
as a relaxation technique. One example
is SAMONAS Sound Therapy CDs, which claim to improve psychological and physical
conditions such as hearing, learning disabilities, voice problems and
behavioral disturbances (SAMONAS).
SAMONAS is an acronym for “Spectral Activated Music of Optimal Natural
Structure”. The sixty minute CD titled
“Mystery of Water” stimulates the human consciousness, generating creativity,
fantasy and imagination. The high
frequency sound matrix of the CD enhances alertness in the temporal lobe of the
human brain (SAMONAS). This creates a
neurological effect in many areas of the body and on the psychological level of
human hearing (SAMONAS). The sound of
water reflects the energy of life in its movements and it awakens the body’s
memories of past experiences through the sense of hearing.
Another
product that uses the sound of water is Conair Sound Therapy Deluxe Relaxation
System with Dual Alarm Clock Radio. For
$48.99 you can wake up and fall asleep to nature’s soothing sounds such as
ocean waves, a stream, rainfall, a thunderstorm, or a waterfall. I own a similar product, the Brookstone
Tranquil Moments for Travel Relaxation Sound System. It advertises that the surf provides a calm rhythm that helps you
drift off to sleep or creates a relaxing oceanside environment. The mountain stream helps you unwind and
provides great background sound for everyday activities. The tranquil rainfall and the steady flow of
the waterfall are both peaceful sounds, which mask unwanted background
noise. I used my Relaxation Sound
System for a couple months after I purchased it and my favorite sound is the
forest rainfall. It reminds me of the
rain hitting the leaves at my house in New England. The constant rhythm is relaxing and it makes me feel nostalgic,
peaceful and sleepy.
Another
time when the sound of water may be useful is during pregnancy and during
labor. The sound helps to create a
state of deep relaxation and the emotional and
meditative aspects of giving birth are enhanced. The sound of water in the delivery room can help the baby’s
transition from the womb into the air of the world.
Modern
society has greatly benefited from the research of how sound travels underwater
and from the research of how the sound of water is therapeutic. The sound of water can be useful for
meditation during pregnancy and it can improve psychological and physical
conditions such as learning disabilities and behavioral disturbances. Underwater acoustic techniques are used to
monitor the climate, research ocean wildlife, detect military submarine
warfare, and for commercial purposes.
Underwater technologies such as hydrophones can detect the presence of
commercially valuable fish and underwater speaker systems can be used for
entertainment and during water sports.
Works Cited
“The Physics of Diving: Sound and
Hearing.” Online. Internet.
13 Apr. 2001.
Available http://library.thinkquest.org/28170/36.html
“Underwater Applications.” Online.
Internet. 23 Apr. 2001
Available
http://www.itc-transducers.com/168-0018.htm
http://www.itc-transducers.com/168-0009.htm
“Nova Online: Submarines, Secrets and
Spies.” Online. Internet.
25 Apr.
2001. Available http://www.pbs.org/wgbh/nova/subsecrets/sounds01false.html
“Beyond Discovery: Propagagtion of Sound in
the Ocean.” Online. Internet.
25 Apr. 2001 Available
http://www4.nas.edu/beyond/beyonddiscovery.nsf/web/ocean5?
“Probing the Ocean Interior with Sound.” Online.
Internet. 25 Apr. 2001
Available http://www4.nas.edu/beyond/beyonddiscovery.nsf/web/ocean8