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Physics of Sound Part 1

Physics of Sound Part 1. Sound waves How they are generated and travel. Sound Waves. Generation and Propagation Sound wave = changes in pressure caused by vibrating object Compression = High pressure Rarefaction = Low pressure Sound needs a medium to “vibrate”

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Physics of Sound Part 1

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  1. Physics of SoundPart 1 Sound waves How they are generated and travel

  2. Sound Waves • Generation and Propagation • Sound wave = changes in pressure caused by vibrating object • Compression = High pressure • Rarefaction = Low pressure • Sound needs a medium to “vibrate” • Usually air, but could be anything • Speed of sound depends upon the medium

  3. Measuring sound waves • Sound waves are longitudinal waves • Vibrating object compresses the air around it. • Pushes air away leaving an area of low pressure • Vibrating object then compresses more air to create a “chain”

  4. Measuring methods Cycle • A single push and pull of the vibrating object • One are of compression followed by one area of rarefaction • An initial increase in atmospheric pressure from the norm, followed by a drop below the norm and then a return to normal • Mathematically displayed by a sine curve • Pressure on Y axis • Time on X axis

  5. Measuring methods Period (T) and Frequency (f) • Period - The time it takes to create one cycle • Frequency - The number of cycles in one second • Measured in Hertz (Hz) or cycles per second

  6. Measuring methods Example It takes ¼ sec to create one cycle. What is the sound wave’s frequency?

  7. Measuring methods • Frequency will determine pitch • High frequency = high pitch • Low frequency = low pitch • Octave – a doubling of halving of the frequency

  8. Measuring methods • Human hearing range • Low range between 15 to 30 Hz • With enough power lower than 15 Hz can be felt, buy not heard as “sound” • High range varies with age and gender • Women - up to 20 kHz • Men – between 15 to 18 kHz • High frequency range will lower with exposure to high levels of sound and age

  9. Tuning • Traditional orchestra would tune First Chair Violin A first. • Remaining instruments would tune relative to that • A above middle C was tuned to about 420 Hz • As halls grew larger it was found to be desirable to tune sharper • 1939 A was established to be 440 Hz • Corresponds to the 49th key on a full size piano • Tuning is not a science. The relative frequency difference is what is important

  10. Measuring methods Wavelength • The distance from one area of compression to the next or one area of rarefaction to the next l=wave length V = velocity of sound in medium usually 1130 ft/sec f = frequency

  11. Measuring methods • Amplitude • How high the pressure goes above and below normal atmospheric pressure • Corresponds to how loud the sound is • “loudness” is relative to frequency and dependant on the listener.

  12. Timber and Harmonics • Harmonics – multiples of a base frequency • Timber – the characteristics of a particular sound or instrument • Different harmonics combined in different levels • White Noise • Contains all frequencies at equal power • Equivalent to white light • Pink Noise • Contains all frequencies at equal power per octave • Homework • Read http://harada-sound.com/sound/handbook/

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