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Title:

Sound

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Title: Sound Author: Cherie Lehman Last modified by: Cherie Lehman Created Date: 1/15/2007 10:58:15 PM Document presentation format: On-screen Show – PowerPoint PPT presentation

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Title: Sound


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 gt20,000 Hz
  • Infrasound lt 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 0C 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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