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Sound

Sound. Sound Waves. The origin of any sound is a vibrating object Usually the frequency of the sound is the same as that of the vibrating object Frequency Range: Sound: 20 Hz – 20,000 Hz Ultrasound: >20,000 Hz Infrasound: < 20 Hz. Forced Vibration & Resonance.

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Sound

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  1. Sound

  2. Sound Waves • The origin of any sound is a vibrating object • Usually the frequency of the sound is the same as that of the vibrating object • Frequency Range: Sound: 20 Hz – 20,000 Hz Ultrasound: >20,000 Hz Infrasound: < 20 Hz

  3. Forced Vibration & Resonance • forced vibration – example -- strike tuning fork and hold the stem against the table • sounding board -- used to amplify sound in music boxes and all string • resonance -- when the frequency of forced vibrations matches the object's natural frequency, a dramatic increase in amplitude occurs

  4. Speed of Sound • depends on wind conditions, temperature, and humidity • does NOT depend on loudness or frequency of the sound • all sounds travel at the same speed in the same medium in dry air at 0°C ~ 330 m/s (1200 km/h) • Sound travels faster through warm air than cold air. • In air, vsound = 330 m/s + (0.6 m/s/Co)*TC

  5. Pitch & Loudness • Pitch – frequency Double frequency – go up an octave • Loudness – amplitude

  6. Decibel Scale • incredibly sensitive • can hear everything from fingertip brushing lightly over fabric to a loud jet engine • sound of jet engine is about 1012 times more powerful than smallest audible sound • a big difference! • decibel scale -- smallest audible sound is 0 dB • A sound 10 times more powerful is 10 dB • A sound 100 times more powerful than near total silence is 20 dB Decibel Scale is logarithmic

  7. Decibel Levels • Near total silence - 0 dB • A whisper - 15 dB • Normal conversation - 60 dB • A lawnmower - 90 dB • A car horn - 110 dB • A rock concert or a jet engine - 120 dB • A gunshot or firecracker - 140 dB

  8. Waves Moving in and Out of Phase • When the 2 waves are in phase, the resulting disturbance has a maximum amplitude. • When the 2 waves are out of phase, the resulting disturbance has a minimum amplitude.

  9. Beats • Waves of slightly different frequencies form a pattern of alternating maximum and minimum amplitude. • The packets of maximum amplitude are called beats.

  10. Noise Canceling • tiny microphones, one on each earpiece, detect ambient noise before it gets to your ears. • noise-cancellation circuitry inverts the captured signal, turning the noise's sound wave upside down. • noise-cancellation system adds the sonic opposite of the external noise to whatever you're listening to • eliminating most of the pollution and leaving you with just your music.

  11. Standing Waves • http://phet.colorado.edu

  12. Fundamental & Harmonics

  13. To Do • Read Chapter 20 • Complete Homework 1 due Tues, Jan. 23 • Remember – NO CLASS ON Thursday, Jan. 18

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