Music Acoustics

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Music Acoustics
2014-01-30 20:42:33
Music Acoustics

Note cards on acoustics
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  1. Vibration
    any form of to-and-fro motion, aka oscillation
  2. Sound
    A perceived, aural psychological sensation produced by vibration
  3. Sine Wave
    graph of the simplest form of vibration showing motion in time and space
  4. Sine Tone
    the sound produced by sinusoidal vibration or oscillation; also known as a pure tone
  5. Simple Harmonic Motion
    simple vibration; motion that takes place in a straight line and is periodic
  6. Elasticity
    Natural tendency of a displaced body to return to its point of rest
  7. Momentum
    tendency of a displaced body to overshoot its point of rest
  8. Frequency
    number of cycles (complete vibrations) which take place in one second; also the # of sound waves passing a given point in one second
  9. Resonant frequency
    frequency at which a body tends to vibrate due to its natural characteristics of size, shape, molecular composition, and the stress it is under
  10. 3 Main Factors affecting Resonant Frequency:
    Material, whether or not it is under stress, and its proportions. Ex: string: length and thickness, tension, material of string
  11. Pitch
    Our perception of frequency (an aural sensation).  Greater the frequency, the higher the perceived pitch. Rate of vibration is pitch
  12. Amplitude
    distance thru which a vibrating body moves; aka amount of displacement of a vibrating body
  13. Loudness
    perception of amplitude.  greater the amp, the louder it is perceived; also depends on where the fre/am of material vibrating lies w/in limits of human hearing
  14. Hearing Loss
    Inability to perceive certain frequencies and amplitudes which are within the common limits of perception
  15. Human range of frequencies
    No lower than 20Hz and no higher than 20,000 Hz

    as we get older: upper limit 10,000 Hz
  16. Cent
    One hundredth of a chromatic semitone; unit most used to represent pitch deviation
  17. Decibel
    • Unit of sound intensity; relationship bt sound being measured and a reference intensity upon which the sound level meter is calibrate
    • Is approx smallest change in intensity the human ear can detect
  18. dB level at which pain occurs:
    120 dB
  19. Transmitting medium
    transmitter of vibration from a sound source to a receiver; must be plastic in order for vibration to take place
  20. Compression
    point in space where a number of molecules which have been set into motion in effect bunch up causing an unusual number of molecules to occupy the same space
  21. Rarefaction
    point at which usual number of molecules which occupy a given space are temporarily out of position, causing a partial vacuum to occur
  22. Reflection
    bouncing back of sound waves as they strike a surface more dense than that in which they are traveling
  23. Echoes
    sound waves which have been reflected; do not disturb the frequency of other wavefronts
  24. Speed at which sound waves travel
    1100 ft per second, aka 4.7 seconds for 1 mile
  25. Resonance
    transmission of vibration from one body to another, usually through the air.  aka sympathetic vibration; fre of 1st body must be exactly or very near the nat'l frequency of 2nd body
  26. Sympathetic vibration
    excitation of a second sound source
  27. Timbre
    sensory characteristic determined mainly by the degree of complexity of the vibration of a body
  28. Fundamental frequency
    frequency at which the sound source vibrates as a whole; also expressed as the lowest pitch that the sound source is capable of producing
  29. Overtones
    one of the frequencies produced by the complex vibration of a body; is a whole number multiple of the fundamental
  30. Harmonics
    a series of tones (overtones) caused by the complex vibration of a body; fundamental frequency referred to as the 1st harmonic
  31. Partial
    any component of the harmonic series including the fundamental.  often the terms o,h, and p are used interchangeably
  32. Formants
    Frequencies which are more resonant than others
  33. Envelope
    the temporal shape of a tone consisting of an attack, initial decay, sustain, and final decay
  34. 4 Parameters of sound:
    frequency, amplitude, timbre, and envelope
  35. Noise
    complex sounds which are aperiodic and contain overtones which are not part of the nat'l harmonic series
  36. Inharmonic overtones
    Those frequencies above a fundamental tone which are not a whole-number multiple of the fundamental; have inconsistencies of tension, tress, and configuration
  37. White Noise
    random occurrence of all pitches at equal amplitude within the audible frequency spectrum
  38. Ambience
    composite of sound in a particular environment; all sounds present except the sounds you are trying to attend to
  39. Masking
    process by which the threshold of audibility of one set of sounds is raised by the present of another set of sounds; amt of masking effect usually expressed in dB
  40. Standing Wave
    regular and repeated excitation of energy traveling back and forth gives appearance that the wave is standing still; have loops and nodes
  41. Transverse Wave
    • waves in which the molecules of the transmitting medium were disturbed at right angles to the sound source
    • ex: tuning fork
  42. Longitudinal wave
    • molecules of transmitting medium are disturbed in the same direction as the sound source
    • ex: coiled spring in cylinder; hit at one end and spring moves back & forth (see - slinky)
  43. Stringed instrument
    Sound source is stretched, vibrating string over a resonating air chamber; 2 categories: length of string changed w/fingers and strings of fixed length
  44. Artificial Harmonics
    tones produced on stringed instruments by lightly touching a point along the string's length as it is bowed where a node exists
  45. Damping
    suppression of vibration by applying physical restraint
  46. Torsional vibrations
    to-and-fro movement in a twisting direction; creates more complex vibrations
  47. Frets
    Metal inlays in the fingerboard of some stringed instruments that fix length of the string when the finger presses behind them
  48. Wind instrument
    uses reed or edge tone to produce periodic puffs of air and resonate a column of air
  49. edge tones
    • vibes caused by eddies (vortices) of air which are produced by a stream of air blown across the edge of a plate
    • low intensity and high frequency
    • wave 2x long as pipe
  50. reeds
    • any object or pair of objects which, when vibrated at the closed end of a pipe, sets the air in the pipe into vibration
    • longitudinal and transverse vibrations
  51. Bore
    Size (diameter) of the inside of a pipe
  52. Trachea
    windpipe or tube from the lungs to the throat and mouth; vocal folds lie at top and across of trachea forming the glottis
  53. Glottis
    Opening bt the vocal folds
  54. Percussion
    sound source of either vibrating membranes or vibrating solid bodies; inharmonic overtones
  55. Stretched membranes
    ...Membranes stretched over a frame which are struck
  56. Chladni figures
    Acoustic pictures that show where the loops and nodes are located on the stretched membrane
  57. Speed of Sound
    speed at which sound travels... at 68 d F, 1130 fps; 32 travels at 1088
  58. Wave Front
    • shape or configurations of the component compressions and rarefactions as they diffuse through a medium
    • leave at speed of sound over ever-widening area
  59. Diffusion
    dissipation of sound energy or weakening of wave trains as they travel thru a medium
  60. Range at which human ear is most sensitive
    1000-5000 Hz
  61. Refraction
    bending of wave fronts as they pass through mediums having unequal or varying density
  62. Diffraction
    spreading out of wave fronts into areas behind and around physical barriers; filling-in of areas or spaces behind physical barriers that are blocks and not in a straight line from the sound source
  63. Interference
    When there is more than one sound source present
  64. Beats
    Periodic reinforcement and cancellation of two wave fronts with frequencies closer together than 20 Hz
  65. Subjective tones
    do not exist in environment, but by forcing parts of the air into non-linear vibration, are created w/in the ear itself
  66. difference tones
    periodic reinforcement and cancellation of two wave trains with the frequency further apart than 20Hz may be perceived as a 3rd tone whose frequency is the difference bt the frequencies of the original tones
  67. summation tones
    subjective tones produced by the ear that are perceived as the sum of 2 external frequencies
  68. Reverberation
    perceived phenomenon of multiple echoes mixing with the primary sound
  69. absorption
    trapping of sound waves in fibrous or porous materials which weakens the wavefront by reflecting and diffusing sound energy
  70. Insulation
    preventing sound waves from traveling thru physical barriers thru combinations of reflection,absorption,diffusion, or creating a barrier
  71. Diaphragm
    Thin membrane or disk that receives and transmits transverse acoustic vibrations
  72. Fidelity
    degree of accuracy of reproduction of an acoustical phenomenon replicated by an electrical sound system, both in amp and fre
  73. conductor:
    any material that easily allows electric current to pass thru it
  74. Current
    rate of flow of electricity
  75. circuit
    complete path of an electric current, usually including the generator
  76. Generator
    transducer of mechanical energy into electrical energy
  77. Magnetic field
    force which surrounds magnets; circulation of electrons that constantly moves thru a magnet creating a field of force