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Sound waves are detected by the fact
that they cause objects to vibrate. Your ear and a
microphone are common detectors of sound. They work by
converting the sound wave into a signal and then
amplifying and processing that signal.
Questions you may have about sound are:
Just as a vibrating object creates
sound, thus forming compression waves in air or some
other medium, sound is also detected by the waves
causing a back-and-forth vibration of some object in its
path.
You can feel how sound can cause other
things to vibrate by standing in front of some
loudspeakers when music is being played very loud. You
can actually feel the vibration on your skin and chest.
Loud sounds in a room can cause the
windows and even walls to vibrate at the frequency of
the waveform.
The detection of sound waves requires
transferring the vibration it causes into some sort of
signal that can be processed and used.
Feeling the vibration of a wall when
loud music is being played in the other room is
detecting the sound, by changing the vibration into
signals to your brain from your sense of touch. But that
isn't very useful information.
Your ear or a microphone can convert the
vibration into a signal, which can then be processed
into a form that can duplicate or reproduce that sound.
The type of signal that the vibration
creates is usually an electrical signal. Processing can
almost duplicate the original sound, except for some
distortions.
Detectors
There are a number of devices used to
detect sound. The most common are the ear and the
microphone.
The ear has a small membrane called an
eardrum. Sound causes to the membrane to vibrate, which
in turn cause tiny hairs in your inner ear to vibrate,
according to their designated frequency. Each hair sends
an electrical impulse to the brain, where the signals
are process and turned into the perception of sound.
The most common mechanical detector of
sound is the microphone. It has a membrane that is made
to vibrate by the sound. That vibration is changed to
electrical signals, which are then sent to a processor
or electronic circuitry for amplification or such.
The electrical signal can then be sent
to a loudspeaker to create sound at a greater volume, to
a tape recorder, or to send out radio or TV signals.
The secret agencies in various countries
often try to spy on their opponents to gain information.
They may try to "bug" an office by hiding tiny
microphones in areas where they can listen in on
conversations.
They have also devised some very clever
ways of detecting sounds and conversations at a
distance.
The American intelligence agencies have
used lasers to detect conversations. From a distance
outside, they would shine a small, invisible laser spot
on a window of a building where secret conversations
where being held. The reflected light off the window
would be distorted due to the subtle vibrations of the
glass from the conversations inside the room.
The device would detect the reflected
light and convert it into electrical signals.
The Russian or Soviet Union secret
service went one-up on this device. Since people were
aware of the possibility of someone bugging their office
or using a laser on a window to detect conversations in
an office, they would often hold their secret
conversations out in the park, away from any spy
devices.
To spy on such conversations, the KGB
developed a powerful telescope with a laser that could
actually detect vibrations off a blade of grass near the
people having the conversation.
Although it isn't ethical for the
average person to spy on someone else's conversation, it
does illustrate how sound causes vibrations that can be
detected, processed and used.
Sound causes objects to vibrate, which
is used to detect and process the sound. The ear and a
microphone are common detectors of sound, although there
are also some clever devices to detect sound at a
distance. |
