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  1. 1. Chapter 15 – Sound
  2. 2. All sounds are caused by vibrations <ul><li>Vibration – back and forth movement of matter. </li></ul><ul><li>Sound waves are generated by any vibrating object </li></ul><ul><li>The vibrations create molecular motions and pressure oscillations in the air </li></ul><ul><li>The oscillations create a periodic disturbance of the surrounding air </li></ul><ul><li>The effect of these waves is heard as sound </li></ul>
  3. 3. <ul><li>The human voice comes from vibrations of the vocal cords </li></ul><ul><li>Air from the lungs is what causes the vocal cords to vibrate </li></ul><ul><li>The frequency of vibration is controlled by the singer’s muscular tension placed on the cords </li></ul><ul><li>The human voice uses the throat and mouth cavity as a resonator </li></ul>The Human Voice
  4. 4. <ul><li>BRASS </li></ul><ul><ul><li>The lips of the performer vibrate resulting in sound </li></ul></ul><ul><li>REED </li></ul><ul><ul><li>Have a thin wooden strip that vibrates as a result of air blown across it </li></ul></ul><ul><li>WIND </li></ul><ul><ul><li>The air blown across the opening in the pipe (mouthpiece) sets the column of air in the instrument into vibration </li></ul></ul><ul><li>STRING </li></ul><ul><ul><li>A wire or string is set into vibration. The wire is attached to a sounding board that vibrates with the string </li></ul></ul>Source of Sound in Instruments
  5. 5. Sound waves are longitudinal  
  6. 6. Sound waves travel faster as medium it travels through becomes warmer. <ul><li>Speed of sound in various mediums Air 340 m/s Water 1500 m/s Iron 5100 m/s </li></ul>
  7. 7. Loudness Vs. Intensity <ul><li>Loudness – perception of the rate at which sound energy enters your ear.   </li></ul><ul><li>Intensity – Measurement of amplitude.   </li></ul><ul><li>Intensity and loudness decreases with distance   </li></ul>
  8. 8. Intensity <ul><li>Decibel (dB) Unit of intensity level – compares to lowest possible limit of human hearing </li></ul><ul><li>Typical intensity levels Breathing 10 dB Whisper 30 dB Loud stereo 90 dB Jet 150 dB   </li></ul>
  9. 9. Sound waves that enter your ear cause the eardrum to vibrate. <ul><li>Intensity levels greater than 90 dB can cause hearing loss.  </li></ul>
  10. 10. Frequency and Pitch   <ul><li>Pitch – the perception of frequency Humans can detect a wide range of frequencies and are sensitive to a large range of amplitudes. </li></ul><ul><li>Humans (hearing) 20-20 000 Hz </li></ul><ul><li>Humans (making sounds) 85-1100 Hz Bat 1000 – 120 000 Hz Dog whistle 20 000 – 24 000 Hz   Waves with frequencies greater than 20,000 Hz are called Ultrasonic.   Waves with frequencies less than 20,000 Hz are called Subsonic . </li></ul>
  11. 11. Reflection of Sound Waves <ul><li>Echo – reflected sound wave </li></ul><ul><li>Follows the Law of Reflection, where the angle of incidence is equal to the angle of reflection. </li></ul><ul><li>Applications: </li></ul><ul><li>Sonar – sound navigation and ranging </li></ul><ul><li>Ultrasound – viewing the fetus in the womb. </li></ul>
  12. 12. Diffraction <ul><li>– bending of sound waves around barriers (you can hear people in the hallway)   </li></ul>
  13. 13. <ul><li>It is divided into three parts: outer ear (pinna), middle ear, inner ear. </li></ul><ul><ul><ul><li>The first chamber of the ear contains tiny hairs and cells that produce ear wax </li></ul></ul></ul><ul><ul><ul><li>Sound waves pass by the pinna and beat against the ear drum, causing it to vibrate </li></ul></ul></ul><ul><ul><ul><li>The vibration of the ear drum causes three bones in the inner ear (hammer, anvil, stirrup) to vibrate carrying motion to the inner ear, which is filled with fluid. </li></ul></ul></ul><ul><ul><ul><li>The cochlea converts the vibration of the bones to nerve impulses that the brain receives via the auditory nerve </li></ul></ul></ul><ul><ul><ul><li>The inner ear also controls balance </li></ul></ul></ul>The Human Ear
  14. 14. Diagram of the Ear
  15. 15. <ul><li>Even though two instruments may be playing the same note, their sounds can differ because each sound contains a number of frequencies with different intensities </li></ul><ul><li>Timbre : the quality of a steady musical sound that is the result of a mixture of harmonics present at different intensities </li></ul>Quality of Sound
  16. 16. Music   <ul><li>Shorter strings produce sounds with higher pitch. (higher frequency) Shorter vibrating columns produce higher pitch. (higher frequency) A vibrating surface is responsible for loudness.     </li></ul>
  17. 17. <ul><li>The variation from soft to loud and back to soft is called a beat </li></ul><ul><li>The number of beats per second corresponds to the difference between frequencies </li></ul><ul><li>The ability to detect beats depends upon an individual’s hearing and musical training. The average human ear can distinguish beats up to a frequency of ten beats per second </li></ul>BEAT
  18. 18. Beats are formed by the interference if two waves of slightly different frequencies traveling in the same direction. In this case one beat occurs at T-2 where constructive interference is greatest. BEAT (continued)
  19. 19. <ul><li>The equation for beat frequency is: </li></ul><ul><li> F=  f 2 -f 1  </li></ul><ul><li>EXAMPLE PROBLEM </li></ul><ul><li>A 420 Hz tuning fork and a 620 Hz tuning fork are struck at the same time. What beat frequency will be produced? </li></ul><ul><li>Solution: </li></ul><ul><li>620-420 = 200, Therefore the beat frequency produced is 200 Hz. </li></ul>BEAT (continued)
  20. 20. <ul><li>When two waves differ by more than 7 Hertz, the ear detects a complex wave. If this resulting sound is: </li></ul><ul><li>unpleasant- Dissonance </li></ul><ul><li>pleasant-Consonance </li></ul>Dissonance Vs. Consonance
  21. 21. The frequency of vibration is called the fundamental frequency of a vibrating string. Because frequency is inversely proportional to wavelength and because we are considering the greatest possible wavelength, the f undamental frequency is the slowest vibration which produces the lowest pitch. Fundamental Frequency = F 1 = V/wavelength = V/2L Fundamentals
  22. 22. <ul><li>Waves of frequencies that are whole number multiples of the fundamental are called harmonics or overtones. </li></ul><ul><ul><li>The fundamental is also called the first harmonic </li></ul></ul><ul><ul><li>Usually the intensity of a higher harmonic is less than the intensity of the fundamental </li></ul></ul>Harmonics
  23. 23. First through Fifth Harmonics
  24. 24. <ul><li>Consists of a large number of frequencies with no relationship to each other </li></ul><ul><li>White noise occurs when all frequencies are present in equal amplitudes. </li></ul><ul><li>The human voice uses the throat and mouth cavity as a resonator </li></ul><ul><ul><li>The quality of the tone depends on the shape of the resonator </li></ul></ul>NOISE
  25. 25. Acoustics <ul><li>– study of how materials influence the production and movement of sound   </li></ul>
  26. 26. <ul><li>Http:// </li></ul><ul><li>www.vistahearing,com/how-ear-works.html </li></ul><ul><li> </li></ul><ul><li> </li></ul>Works Cited
  27. 27. the end