The History of Understanding Sound

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The History of Understanding Sound
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How it all started

• Greek Philosopher Chrysippus (240 BC) emphasized
  that sound exhibits similar behavior to a wave in
  water, which is described as an oscillatory
  disturbance that moves away from some source and
  transports no discernible amount of matter over
  large distance of propagation.

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• The analogy with water waves was strengthened by
  the belief that air motion associated with
  musical sounds is oscillatory and by the
  observation that sound travels with a finite
  speed. Another matter of common knowledge was
  that sound bends around corners, which suggested
  diffraction, a phenomenon often observed in water
  waves.

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• The wave interpretation was also consistent with
  Aristotle's (384-322 B.C.) statement to the
  effect that air motion is generated by a source,
  "thrusting forward in like manner the adjoining
  air, to that the sound travels unaltered in
  quality as far as the disturbance of the air
  manages to reach."

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• A pertinent experimental result, inferred with
  reasonable conclusiveness by the early
  seventeenth century, with antecedents dating back
  to Pythagoras (c. 550 B.C.) and perhaps further,
  is that the air motion generated by a vibrating
  body sounding a single musical note is also
  vibratory and of the same frequency as the body.
  The history of this is intertwined with the
  development of the laws for the natural
  frequencies of vibrating strings and of the
  physical interpretation of musical consonances.

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• Principal roles were played by Marin Mersenne
  (1588-1648), a French natural philosopher often
  referred to as the "father of acoustics," and by
  Galileo Galilei (1564-1642), whose Mathematical
  Discourses Concerning Two New Sciences (1638)
  contained the most lucid statement and discussion
  given up until then of the frequency equivalence.

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• Mersenne's description in his Harmonic
  universelle (1636) of the first absolute
  determination of the frequency of an audible tone
  (at 84 Hz) implies that he already demonstrated
  that the absolute-frequency ratio of two
  vibrating strings, radiating a musical tone and
  its octave, is as 1 2. The perceived harmony
  (consonance) of two such notes would be explained
  if the ratio of the air oscillation frequencies
  is also 1 2, which in turn is consistent with
  the source-air-motion-frequency-equivalence
  hypothesis.

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• The wave viewpoint was not unanimous, however.
  Gassendi (a contemporary of Mersenne and
  Galileo), for example, argued that sound is due
  to a stream of "atoms" emitted by the sounding
  body velocity of sound is the speed of atoms
  frequency is number emitted per unit time.

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• The apparent conflict between ray and wave
  theories played a major role in the history of
  the sister science optics, but the theory of
  sound developed almost from its beginning as a
  wave theory. When ray concepts were used to
  explain acoustic phenomena, as was done, for
  example, by Reynolds and Rayleigh, in the
  nineteenth century, they were regarded, either
  implicitly or explicitly, as mathematical
  approximations to a then well-developed wave
  theory

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Robert Boyle

• Robert Boyle's (1640) classic experiment on the
  sound radiation by a ticking watch in a partially
  evacuated glass vessel provided evidence that air
  is necessary, either for the production or
  transmission of sound.

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Christian Andreas Doppler

• Doppler RADAR is named after Christian Andreas
  Doppler. Doppler was an Austrian physicist who
  first described in 1842, how the observed
  frequency of light and sound waves was affected
  by the relative motion of the source and the
  detector. This phenomenon became known as the
  Doppler effect.
• This is most often demonstrated by the change in
  the sound wave of a passing train. The sound of
  the train whistle will become "higher" in pitch
  as it approaches and "lower" in pitch as it moves
  away. This is explained as follows the number of
  sound waves reaching the ear in a given amount of
  time (this is called the frequency) determines
  the tone, or pitch, perceived. The tone remains
  the same as long as you are not moving. As the
  train moves closer to you the number of sound
  waves reaching your ear in a given amount of time
  increases. Thus, the pitch increases. As the
  train moves away from you the opposite happens.

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Thomas Edison

• The phonograph was developed as a result of
  Thomas Edison's work on two other inventions, the
  telegraph and the telephone. In 1877, Edison was
  working on a machine that would transcribe
  telegraphic messages through indentations on
  paper tape, which could later be sent over the
  telegraph repeatedly. This development led Edison
  to speculate that a telephone message could also
  be recorded in a similar fashion. He experimented
  with a diaphragm which had an embossing point and
  was held against rapidly-moving paraffin paper.
  The speaking vibrations made indentations in the
  paper.

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• Edison later changed the paper to a metal
  cylinder with tin foil wrapped around it. The
  machine had two diaphragm-and-needle units, one
  for recording, and one for playback. When one
  would speak into a mouthpiece, the sound
  vibrations would be indented onto the cylinder by
  the recording needle in a vertical (or hill and
  dale) groove pattern. Edison gave a sketch of the
  machine to his mechanic, John Kreusi, to build,
  which Kreusi supposedly did within 30 hours.
  Edison immediately tested the machine by speaking
  the nursery rhyme into the mouthpiece, "Mary had
  a little lamb." To his amazement, the machine
  played his words back to him.

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Valdemar Poulsen

• Danish telephone engineer and inventor, is best
  known for his Telegraphone, which he patented in
  1898. It was the first practical apparatus for
  magnetic sound recording and reproduction. It was
  an ingenious apparatus for recording telephone
  conversations. It recorded, on a wire, the
  varying magnetic fields produced by a sound. The
  magnetized wire could then be used to play back
  the sound.

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• In 1887, a physicist named Heinrich Hertz began
  experimenting with radio waves in his laboratory
  in Germany. He found that radio waves could be
  transmitted through different materials. Some
  materials reflected the radio waves. He developed
  a system to measure the speed of the waves. The
  data he collected, and the information he
  uncovered, encouraged further scientific
  investigation of radio.

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Sir Robert Alexander Watson-Watt

• Watson-Watt was the Scottish physicist who
  developed the radar locating of aircraft in
  England. In 1917, he worked at the British
  Meteorological Office, where he designed devices
  to locate thunderstorms. Watson-Watt coined the
  phrase "ionosphere" in 1926.  He was appointed as
  the director of radio research at the British
  National Physical Laboratory in 1935, where he
  completed his research into aircraft locating
  devices. Watson-Watt's other contributions
  include a cathode-ray direction finder used to
  study atmospheric phenomena, research in
  electromagnetic radiation, and inventions used
  for flight safety.

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Nixon and Langevin

• Lewis Nixon invented the very first Sonar type
  listening device in 1906, as a way of detecting
  icebergs. Interest in Sonar was increased during
  World War I when there was a need to be able to
  detect submarines. In 1915, Paul Langévin
  invented the first sonar type device for
  detecting submarines "echo location to detect
  submarines" using the piezoelectric properties of
  the quartz. He was too late to help very much
  with the war effort, however, Langévin's work
  heavily influenced future sonar designs.

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History of Sonar

• The first Sonar devices were passive listening
  devices - no signals were sent out. By 1918, both
  Britain and the U.S had built active systems, in
  active Sonar signals are both sent out and then
  received back. Acoustic communication systems are
  Sonar devices where there is both a sound wave
  projector and receiver on both sides of the
  signal path. The invention of the acoustic
  transducer and efficient acoustic projectors made
  more advanced forms of Sonar possible.

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Sonar today

• Sonar is a system that uses transmitted and
  reflected underwater sound waves to detect and
  locate submerged objects or measure the distances
  underwater. It has been used for submarine and
  mine detection, depth detection, commercial
  fishing, diving safety and communication at sea.
  The Sonar device will send out a subsurface sound
  wave and then listens for returning echoes, the
  sound data is relayed to the human operators by a
  loudspeaker or by being displayed on a monitor.

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Robert H Rines

• Robert H. Rines' contributions to the technology
  of high-resolution image-scanning radar and sonar
  began in the era of the Massachusetts Institute
  of Technology's Radiation Laboratory with
  modulation techniques for the Microwave Early
  Warning System developed secretly during World
  War II. In peace time, his inventions were basic
  to high-definition sonar scanning systems used in
  locating the Titanic and the Bismarck. They are
  also used in new medical instrumentation allowing
  noninvasive ultrasound imaging of internal
  organs.

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How small and rapid are the changes of air
pressure which cause sound?

• When the rapid variations in pressure occur
  between about 20 and 20,000 times per second (ie
  at a frequency between 20Hz and 20kHz) sound is
  potentially audible even though the pressure
  variation can sometimes be as low as only a few
  millionths of a Pascal. Movements of the ear drum
  as small as the diameter of a hydrogen atom can
  be audible! Louder sounds are caused by greater
  variation in pressure - 1 Pascal, for example,
  will sound quite loud, provided that most of the
  acoustic energy is in the mid-frequencies (1kHz -
  4kHz) where the ear is most sensitive.