Acoustics - 3-2 - Particle movement& complex sounds...

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Particle movement & complex sounds
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Particles oscillate around their resting point because they are connected by the elastic properties of air. This movement causes areas of high and low pressure in order to propagate a wave Compression/condensation: area of high pressure Rarefaction: area of low pressure Sound is a series of compressions and rarefactions as the wave of disturbance travels along a chain of molecules while the individual molecules move back and forth only around their resting point.
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As the molecules are disturbed from their resting place they disturb adjacent molecules This wave radiates outward from the sound source in the form of a pressure wave This pressure wave is repeated over time – periodic waves are followed by evenly spaced pressure waves. The pressure is related to areas of compression/condensation and rarefaction (high and low pressure areas)
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Longitudinal: particle movement is in the same direction as wave movement
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Transverse waves: particle movement is up and down at right angles to wave movement
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Adding two tones of the same frequency will always result in a sine wave (representation of a pure tone) Adding two tones of different frequencies will result in a complex sound (no longer simple) istics/russell/138/sec4/acoust1.html
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Periodic: repeatable pattern Aperiodic: no repeatable pattern
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Harmonics: whole number multiples of the fundamental Fundamental frequency (F) = the lowest frequency of pattern repetition Fo = H1 Fo x 2 = H2 Fo x 3 = H3 Fo x 4 = H4… As frequency increases, amplitude decreases
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Determine the fundamental by the waveform then to see the amplitude variations of each frequency you must look at a line spectrum.
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