1. 15.1 Properties of Sound

2. Chapter 15 Objectives  Explain how the pitch, loudness, and speed of sound are related to properties of waves.  Describe how sound is created and recorded.  Give examples of refraction, diffraction, absorption, and reflection of sound waves.  Explain the Doppler effect.  Give a practical example of resonance with sound waves.  Explain the relationship between the superposition principle and Fourier’s theorem.  Describe how the meaning of sound is related to frequency and time.  Describe the musical scale, consonance, dissonance, and beats in terms of sound waves.

3. Chapter 15 Vocabulary Terms  acoustics  beats  cochlea  consonance  decibel  dissonance  Doppler effect  Fourier’s theorem  frequency  spectrum  microphone  musical scale  note  octave  pitch  pressure  reverberation  rhythm  shock wave  sonogram  speaker  stereo  subsonic  supersonic

4. Inv 15.1 Properties of Sound Key Question: What is sound and how do we hear it?

5. 15.1 Properties of Sound  If you could see atoms, the difference between high and low pressure is not as great.  The image below is exaggerated to show effect.

6. 15.2 The frequency of sound  We hear frequencies of sound as having different pitch.  A low frequency sound has a low pitch, like the rumble of a big truck.  A high-frequency sound has a high pitch, like a whistle or siren.  In speech, women have higher fundamental frequencies than men.

7. 15.1 Complex sound

8. Common Sounds and their Loudness

9. 15.1 Loudness Every increase of 20 dB, means the pressure wave is 10 times greater in amplitude. Logarithmic scale Linear scale Decibels (dB)Amplitude 01 2010 40100 601,000 8010,000 100100,000 1201,000,000

10. 15.1 Sensitivity of the ear  How we hear the loudness of sound is affected by the frequency of the sound as well as by the amplitude.  The human ear is most sensitive to sounds between 300 and 3,000 Hz.  The ear is less sensitive to sounds outside this range.  Most of the frequencies that make up speech are between 300 and 3,000 Hz.

11. 15.1 How sound is created  The human voice is a complex sound that starts in the larynx, a small structure at the top of your windpipe.  The sound that starts in the larynx is changed by passing through openings in the throat and mouth.  Different sounds are made by changing both the vibrations in the larynx and the shape of the openings.

12. 15.1 How sound is created  A speaker is a device that is specially designed to reproduce sounds accurately.  The working parts of a typical speaker include a magnet, a coil of wire, and a cone.

13. 15.1 Recording sound  A common way to record sound starts with a microphone.  The microphone transforms a sound wave into an electrical signal with the same pattern of oscillation.  In modern digital recording, a sensitive circuit converts analog sounds to digital values between 0 and 65,536.

14. 15.1 Recording sound  Numbers correspond to the amplitude of the signal and are recorded as data. One second of compact- disk-quality sound is a list of 44,100 numbers.

15. 15.1 Recording sound  To play the sound back, the string of numbers is read by a laser and converted into electrical signals again by a second circuit which reverses the process of the previous circuit.

16. 15.1 Recording sound  The electrical signal is amplified until it is powerful enough to move the coil in a speaker and reproduce the sound.