Sound & Music

1. Sound & Music Conceptual Physics

2. Origin of Sound Sound is a wave that is produced by the vibrations of material objects. Drumhead Guitar string Tuning fork Physics 1 (Garcia) SJSU

3. The Origin of Sound • All sound waves are produced by the vibration of a material object. E.g., the reed of a saxophone, the string of a guitar or the tines of a tuning fork. • Sound waves are longitudinal waves that transport acoustic energy through a medium by particle-to-particle interactions between neighboring molecules as they oscillate back and forth. • The frequency of the sound wave produced is equal to the frequency of the vibrating source. Conceptual Physics Chapter 26

4. The Origin of Sound • The transmission of sound requires a medium. There may be vibrations, but if there is nothing to compress and expand, there can be no sound. • Sound waves can propagate through solids, liquids and gases, but can not travel through a vacuum. Conceptual Physics Chapter 26

5. The Origin of Sound • Sound can be heard from the ringing bell when air is inside the jar, but not when the air is removed. Conceptual Physics Chapter 26

6. Sound in Air Consider sound waves in a tube. • When the prong of a tuning fork next to the tube moves toward the tube, a compression enters the tube. • When the prong swings away, in the opposite direction, a rarefaction follows the compression. • As the source vibrates, a series of compressions and rarefactions is produced. Conceptual Physics Chapter 26

7. The Decibel Scale • Since the range of intensities that can be detected by the human ear is very large, a logarithmic scale, based on powers of ten, is used to measure intensity levels. This intensity level is measured in decibels (dB). • A 50 dB sound is 100 times more intense than a 30 dB sound and 1000 times more intense than a 20 dB sound. Conceptual Physics Chapter 26

8. Nature of Sound in Air Sound in air is a longitudinal wave created by compressions and rarefactions.

9. Demo: Sound is not Wind With sound, air molecules oscillate in place. With wind, air moves from place to place. Smoke rings are not sound because the air moves from place to place. Physics 1 (Garcia) SJSU

10. Demo: Light & Sound Sound waves can only travel through a material, such as air, water, etc. Light and radio waves can travel through vacuum. Radio Wave See the cell phone ringing inside vacuum chamber but don’t hear any sound. Physics 1 (Garcia) SJSU

11. Check Yourself Do light waves have energy? What do we call the type of heat transfer that occurs when light transfers energy? Do sound waves have also have energy? Physics 1 (Garcia) SJSU

12. Media That Transmit Sound Sound travels better through elastic liquids and solids, such as water and rocks, than through air. This is due to the close proximity of the atoms as they vibrate. Hear richer, louder sound transmitted by string Physics 1 (Garcia) SJSU

13. What Your Voice Sounds Like Your voice sounds different to you when you hear it from a recording. This is because when you are speaking aloud, most sound waves reach your ear traveling through the solid flesh and bone of your skull. Leave yourself a voice-mail Physics 1 (Garcia) SJSU

14. Human Ear Pressure variations of sound waves push the eardrum, whose vibrations are transmitted by the ossicles (ear bones) to the cochlea (hearing canal)

15. Cochlea Vibrations transmitted by the ear bones create oscillations in the fluid with the cochlea (snail in Latin), which is a spiral-wrapped tube. These oscillations within the cochlea cause the basilar membrane to ripple, like a waving flag.

16. Organ of Corti The organ of Corti forms a ribbon of sensory epithelium that runs lengthwise down the entire cochlea. The hair cells of the organ of Corti selectively transform the oscillations of the basilar membrane into nerve signals.

17. Loudness & Amplitude Loudness depends on amplitude of pressure and density variations in sound waves. Physics 1 (Garcia) SJSU

18. Decibels Loudness of sound depends on the amplitude of pressure variations in the sound waves. Loudness is measured in decibels (dB), which is a logarithmic scale (since our perception of loudness varies logarithmically). From the threshold of hearing (0 dB) to the threshold of pain (120 dB) the pressure increase is a million times higher. At the threshold of pain (120 db) the pressure variation is only about 10 Pascals, which is one ten thousandths atmospheric pressure.

19. Demo: Make Some Noise Let’s experience the loudness of sound like by clapping at various decibel levels. Sound Meter Start clapping softly and slowly increase or decrease loudness, as I direct you using the sound meter. Physics 1 (Garcia) SJSU

20. Absolute thresholds of hearing by age in males and females Male, Age 60 Male, Age 50 Female, Age 60 Male, Age 40 Male, Age 30 Male, Age 20 Hearing by Age & Sex Hearing acuity decreases with age, especially in the high frequencies. In general, women have greater acoustic sensitivity than men.

21. Hearing Loss The hair cells that line the cochlea are a delicate and vulnerable part of the ear. Repeated or sustained exposure to loud noise destroys the neurons of the Organ of Corti. Once destroyed, the hair cells are not replaced, and the sound frequencies interpreted by them are no longer heard. Hair cells that respond to high frequency sound are very vulnerable to destruction, and loss of these neurons typically produces difficulty understanding human voices. Much of this type of permanent hearing loss is avoidable by reducing exposure, such as to loud music. What?

22. Speed of Sound in Air Speed of sound in air is about 340 m/s. Sound travels about one kilometer in three seconds, about one mile in five seconds. Light is a million times faster than sound. Physics 1 (Garcia) SJSU

23. Demo: Helium Voice Sound speed in helium is higher than speed in air. Wavelength of sound unchanged (size of vocal cords is unchanged). Frequency of voice is higher since Breath Helium… He Talk like me! (Wave speed) (Frequency) = (Wavelength) Physics 1 (Garcia) SJSU

24. Reflection of Sound Sound reflects strongly from rigid surfaces. Softer surfaces absorb sound. Quiet after a fresh snowfall because the soft, irregular surface of the snow absorbs sound instead of reflecting it. Physics 1 (Garcia) SJSU

25. Check Yourself When crowded, which restaurant will be quieter? Physics 1 (Garcia) SJSU

26. Singing in the Shower Multiple reflections from the hard walls create reverberation. Hear your voice from several sources, slightly shifted in time. Reverberation extends each note and smears (smoothens) the pitch. Your voice sounds better when singing in the shower Physics 1 (Garcia) SJSU

27. Refraction of Sound Sound speed can vary by material or conditions. This causes the sound to bend in direction, in the same way that light bends when it passes through a glass lens. Fig. 20.8 Physics 1 (Garcia) SJSU

28. Ultrasound Ultrasound is high frequency (Megahertz), short wavelength (0.1 mm) sound. Reflections and refractions of ultrasound by flesh and bone allow “seeing” inside the human body. Physics 1 (Garcia) SJSU

29. Forced Vibrations Vibrating guitar strings force the vibration of the guitar’s body, producing most of the sound. 731 Hz 553 Hz Circular rings indicate where the surface is vibrating up and down Physics 1 (Garcia) SJSU

30. Demo: Tuning Fork & Sound Box Tuning fork by itself is not very loud. Sound is much louder if it is held against a sound box, such as the body of a guitar or any similar rigid surface. The tuning fork forces the surface into oscillation at the same frequency. Physics 1 (Garcia) SJSU

31. Natural Frequency Metal wrench and wooden bat sound very different when dropped to the floor. Different materials and shapes vibrate at their own natural frequencies. Physics 1 (Garcia) SJSU

32. Demo: Singing Rod Stoking an aluminum rod with rosin-covered fingers induces loud vibrations at the rod’s natural frequency. Physics 1 (Garcia) SJSU

33. Resonance Resonance occurs when forced vibrations match an object’s natural frequency. Oscillations grow in amplitude due to synchronized transfer of energy into the vibrating object. Physics 1 (Garcia) SJSU

34. Acoustic Resonance Sound at an object’s natural frequency can produce resonant vibrations. If the amplitude of the sound is sufficiently large, resonant vibrations can shatter a wine glass. As shown by Myth Busters, this may even be achieved by exceptionally powerful singers (and by average singers using electronic amplifiers).

35. Beats • When two sound waves differing slightly in frequency are superimposed they will not maintain a constant phase relationship. • This leads to alternating reinforcement and cancellation of the sound energy. • The audible result is a series of pulsations called beats. 400 & 401 Hz sounds – 1 beat per second 400 & 403 Hz sounds – 3 beats per second 400 & 410 Hz sounds – 10 beats per second Conceptual Physics Chapter 26

36. Beats • The pattern of alternating constructive and destructive interference can be found from applying the law of superposition to the interfering waves. Conceptual Physics Chapter 26

37. Beats • Beats can occur with any kind of wave and are a practical way to compare frequencies. • To tune a piano, a piano tuner listens for beats produced between a standard tuning fork and a particular string on the piano. • When the frequencies are identical, the beats disappear. • The members of an orchestra tune up by listening for beats between their instruments and a standard tone. Conceptual Physics Chapter 26

38. Tacoma Narrows Bridge In 1940, the first Tacoma Narrows bridge was destroyed by resonance. First Bridge Second Bridge Physics 1 (Garcia) SJSU

39. Movie: Tacoma Narrows Bridge Physics 1 (Garcia) SJSU

40. Chapter 21 Musical Sounds

41. Noise Versus Music • What is the difference between noise and music? • Answer: The appearance of the waveform. Mic&Osc

42. Pitch... • … is the "highness" or "lowness" of a tone. • Pitch corresponds to frequency. • Concert A on the Musical Scale has a frequency of 440 Hertz.

43. Sound Intensity and Loudness • Intensity of Sound • refers to the amplitude of the pressure variations in the sound wave

44. Loudness • the physiological sensation directly related to the sound intensity • measured in bels (1bels = 10 decibels) • b = 10 log(I/Io) • Demo – Sound Meter

45. Source of Sound Loudness (db) Threshold of Hearing 0 Conversation 60 Ear Damage Begins 85 Amplified Music 110 Jet Airplane at 30 meters 140

46. Common Sound Intensities Intensity, I (W/m2) Source of Sound Sound Level, b (db) Threshold of Hearing I0 = 10-12 0 10-11 Rustle of Leaves 10 Whisper 10-10 20 Quiet Radio in Home 10-8 40 10-6 Conversation in Home 60 10-5 70 Busy Street Traffic 10-3 Riveter 90 10-1 Disco Music Amplified 110 1 Air-raid Siren, Nearby 120 102 Jet, 30 m Away 140

47. Loudness • Increase the loudness by 10db and you increase the intensity by 10. • Increase the loudness by 20db and you increase the intensity by 100.

48. Increase the loudness by 30db an you increase the intensity by ... • 10 • 100 • 200 • 1000 • 10000

49. Quality... • …is the characteristic sound that allows us to distinguish between two musical instruments. (a.k.a. timbre) • Partial Tones - one of the many frequencies present in a complex tone • Demo: Guitar String Tones

50. Fundamental Frequency • the lowest frequency of vibration • a.k.a. the first harmonic • Harmonic • a partial tone that is an integer multiple of the fundamental frequency