Sound Waves

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Sound Waves

  1. 1. By iTutor.comT- 1-855-694-8886Email- info@iTutor.com
  2. 2.  Sound is really tiny fluctuations of air pressure– units of pressure: N/m2 or psi (lbs/square-inch) Carried through air at 343 m/s (770 m.p.h) ascompressions and rarefactions in air pressure
  3. 3.  Wavelength () is measured from crest-to-crest– or trough-to-trough, or upswing to upswing, etc. For traveling waves (sound, light, water), there is a speed (c) Frequency (f) refers to how many cycles pass by per second– measured in Hertz, or Hz: cycles per second– associated with this is period: T = 1/f These three are closely related:f = c or Tpressure
  4. 4.  We hear frequencies of sound ashaving different pitch. A low frequency sound has a lowpitch, like the rumble of a bigtruck. A high-frequency sound has ahigh pitch, like a whistle or siren. In speech, women have higherfundamental frequencies thanmen.
  5. 5.  When we hear complex sounds, the nerves in the earrespond separately to each different frequency. The braininterprets the signals from the ear and creates a “sonicimage” from the frequencies. The meaning in differentsounds is derived from the patterns in how the differentfrequencies get louder and softer.
  6. 6.  How we hear the loudnessof sound is affected by thefrequency of the sound aswell as by the amplitude. The human ear is mostsensitive to sounds between300 and 3,000 Hz. The ear is less sensitive tosounds outside this range. Most of the frequencies thatmake up speech are between300 and 3,000 Hz.
  7. 7. 1. A common way to record sound starts with amicrophone. A microphone transforms a soundwave into an electrical signal with the samepattern of oscillation.
  8. 8. 2. In modern digital recording, a sensitive circuitconverts analog sounds to digital values between 0and 65,536.
  9. 9. 3. Numbers correspond to the amplitude of the signaland are recorded as data. One second of compact-disk-quality sound is a list of 44,100 numbers.
  10. 10. 4. To play the sound back, the string of numbers isread by a laser and converted into electrical signalsagain by a second circuit which reverses theprocess of the previous circuit.
  11. 11. 5. The electrical signal is amplified until it is powerfulenough to move the coil in a speaker and reproducethe sound.
  12. 12.  A sound wave is a wave of alternating high-pressureand low-pressure regions of air. Sound is a longitudinal wave, meaning that the motionof particles is along the direction of propagation
  13. 13.  Waves in air can’t really be transverse, because theatoms/molecules are not bound to each other– can’t pull a (momentarily) neighboring molecule sideways– only if a “rubber band” connected the molecules would this work– fancy way of saying this: gases can’t support shear loads Air molecules can really only bump into one another
  14. 14.  The pitch of a sound depends on the frequency ofthe tone that the ear receives. High notes areproduced by an object that is vibrating a greaternumber of times per second than for a low note The intensity of a sound is the amount of energycrossing a unit area in unit time or the powerflowing through the unit area. The SI unit is wattsper square meter. The loudness of the sound depends upon thesubjective effect of intensity of sound waves on thehuman ear.
  15. 15.  The shift in frequency caused by motion is called theDoppler effect. It occurs when a sound source is moving at speeds lessthan the speed of sound.
  16. 16.  Any waveform can beanalyzed as the sumof a set of sine waves,each with a particularamplitude, frequency,and phase.
  17. 17.  The speed of sound in air is 343 meters per second(660 miles per hour) at one atmosphere of pressureand room temperature (21°C). An object is subsonic when it is moving slower thansound.
  18. 18.  We use the term supersonic to describe motion atspeeds faster than the speed of sound. A shock wave forms where the wave fronts pile up. The pressure change across the shock wave is whatcauses a very loud sound known as a sonic boom.
  19. 19.  A complex wave is really a sum of component frequencies. A frequency spectrum is a graph that shows the amplitudeof each component frequency in a complex wave.
  20. 20.  A single frequency by itself does not have much meaning. The meaning comes from patterns in many frequenciestogether. A sonogram is a specialkind of graph that showshow loud sound is atdifferent frequencies. Every person’s sonogramis different, even whensaying the same word.
  21. 21.  The eardrum vibratesin response to soundwaves in the ear canal. The three delicatebones of the inner eartransmit the vibrationof the eardrum to theside of the cochlea. The fluid in the spiralof the cochlea vibratesand creates waves thattravel up the spiral.
  22. 22.  The nerves near thebeginning see arelatively large channeland respond to longerwavelength, lowfrequency sound.The nerves at the smallend of the channelrespond to shorterwavelength, higher-frequency sound.
  23. 23.  The pitch of a sound is how high or low we hear itsfrequency. Though pitch and frequency usually meanthe same thing, the way we hear a pitch can beaffected by the sounds we heard before and after. Rhythm is a regular time pattern in a sound. Music is a combination of sound and rhythm that wefind pleasant. Most of the music you listen to is created from apattern of frequencies called a musical scale.
  24. 24.  Harmony is the study of how sounds work together tocreate effects desired by the composer. When we hear more than one frequency of sound and thecombination sounds good, we call it consonance. When the combination sounds bad or unsettling, we call itdissonance.
  25. 25.  Consonance and dissonance are related to beats. When frequencies are far enough apart that thereare no beats, we get consonance. When frequencies are too close together, we hearbeats that are the cause of dissonance. Beats occur when two frequencies are close, butnot exactly the same.Beats are created by the interference of two waves with different frequencies.
  26. 26.  A listener will hear the alternating loudness, knownas beats. The number of beats per second, called the beatfrequency, equals the difference between thefrequencies of the two individual waves. To tune an instrument accurately, a musicianlistens carefully and adjusts her instrument toeliminate beats between the instrument and a givenpitch.
  27. 27.  Echolocation is the methodof detecting objects byemitting a sound, receivingthe echo and correctlyidentifying the location, sizeand structure of the object. These sound waves are veryhigh-pitched, and mosthumans are unable to hearthem.
  28. 28.  The same note sounds different when played on differentinstruments because the sound from an instrument is nota single pure frequency. The variation comes from the harmonics, multiples ofthe fundamental note.
  29. 29. The EndCall us for more informationwww.iTutor.comVisit1-855-694-8886

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