2. The wavelength, λ, is 20 m. What is the speed of this wave? CT 2.1.10 3 Time (sec) A) 1 m/s B) 6 m/s C) 10 m/s D) 15 m/s E) None of the above/not enough info/not sure

3. Sound Chapter 15

4. Perceiving Sound

5. What is sound? Sound is a longitudinal wave which travels through the air through a series of compressions and rarefactions.

6. Sound Waves Sound travels different speeds in different media. Sound typically travels faster in a solid that a liquid and faster in a liquid than a gas. Sound travels different speeds in different media. Sound typically travels faster in a solid that a liquid and faster in a liquid than a gas. The higher the temperature, the faster the particles of the medium will move and the faster the particles will carry the sound. The higher the temperature, the faster the particles of the medium will move and the faster the particles will carry the sound. Medium (C o )m/s Air (0 o )331 Air (20 o )343 Helium (0 o )972 Water (25 o )1493 Seawater (25 o )1533 Copper (25 o )3560 Iron (25 o )5130 Speed of Sound Sound waves move through air because of regular variations or oscillations in air pressure Sound waves move through air because of regular variations or oscillations in air pressure

7. Perceiving Sound Pitch – Frequency of vibrations We can hear frequencies from 20 Hz to 20,000 Hz are infrasonic. A high-pitched sound has a high frequency (a screaming girl). A low-pitched sound has a low frequency (a fog-horn). By the time you’re age 70, you can’t hear frequencies above 8,000 Hz…That’s why older people have a hard time hearing. Sounds above 20,000 Hz are termed ultrasonic. Some animals, such as dogs, can hear frequencies in this range in which humans cannot hear.

8. Sound Waves On a longitudinal wave the area squeezed together is called the compression. The areas spread out are called the rarefaction. The wavelength is the distance from the center of one compression to the center of the next compression.

9. What is the Doppler Effect ? The Doppler Effect is the apparent change in frequency detected when the sound is moving relative to the hearer. Video-Excellent example of Doppler Effect with car horn (26 seconds)Excellent example of Doppler Effect with car horn Video-A Motorcycle does the Doppler Effect (27 seconds)A Motorcycle does the Doppler Effect

10. Doppler Effect The effect that explains why a moving sound will sound different when a sound is coming towards you or away from you. The effect that explains why a moving sound will sound different when a sound is coming towards you or away from you. The frequency perceived by a detector is equal to the velocity of the detector relative to the velocity of the wave, divided by the velocity of the source relative to the velocity of the wave, multiplied by the wave’s frequency. The frequency perceived by a detector is equal to the velocity of the detector relative to the velocity of the wave, divided by the velocity of the source relative to the velocity of the wave, multiplied by the wave’s frequency.

11. You hear an increasing pitch of an ambulance. Draw a picture that describes this process.

12. Which picture(s) describes this process? You hear an increasing pitch of an ambulance. vpvp v a = 0 vpvp vava v p = 0 vava 1 4 2 3 5 1 & 2 63 & 4 71 & 4 82 & 3

13. Doppler Effect - Example A trumpet player sounds C above middle C (524 Hz) while traveling in a convertible at 24.6 m/s. If the car is coming toward you, what frequency would you hear? Assume that the temperature is 20 o C. A trumpet player sounds C above middle C (524 Hz) while traveling in a convertible at 24.6 m/s. If the car is coming toward you, what frequency would you hear? Assume that the temperature is 20 o C.

14. What is sound intensity? Sound intensity is the energy that the sound wave possesses. The greater the intensity of sound the farther the sound will travel and the louder the sound will appear.

15. Sound intensity - Problem What is the intensity of the sound waves produced by a trumpet at a distance of 3.2 m when the power output of the trumpet is 0.20 W? Assume that the sound waves are spherical.

16. Problems You are in an auto traveling at 55 mph (24.6 m/s). A second auto is moving toward you a the same speed. Its horn is sounding at 475 Hz. What frequency do you hear? Use 343 m/s as the speed of sound. You are in an auto traveling at 55 mph (24.6 m/s). A second auto is moving toward you a the same speed. Its horn is sounding at 475 Hz. What frequency do you hear? Use 343 m/s as the speed of sound. At a maximum level of loudness, the power output of a 75-piece orchestra radiated as sound is 70.0 W. What is the intensity of these sound waves to a listener who is sitting 25.0 m from the orchestra? At a maximum level of loudness, the power output of a 75-piece orchestra radiated as sound is 70.0 W. What is the intensity of these sound waves to a listener who is sitting 25.0 m from the orchestra?

17. Perceiving Sound Loudness - Dependent on amplitude Loudness - Dependent on amplitude Remember – amplitude for a longitudinal wave is the closeness of the compression Remember – amplitude for a longitudinal wave is the closeness of the compression Loudness is very closely related to intensity. Loudness is the human perception of the sound intensity. The unit for loudness is decibels.

18. Amplitude - Sound

19. Intensity vs. Decibel

20. Loudness in Decibels

21. Harmonics…. Standing Waves for Strings 1 =2L f1f1 Fundamental frequency 2 =2/2Lf 2 =2f 1 2 nd harmonic 3 =2/3Lf 3 =3f 1 3 rd harmonic 1 =2/4L f 4 =4f 1 4 th harmonic 1 =2/5Lf 1 =5f 1 5 th harmonic

22. Although we would perceive a string vibrating as a whole, it actually vibrates in a pattern that at first appears to be erratic producing many different overtone pitches. What results are particular tone colors or timbres of instruments and voices. it actually vibrates in a pattern that at first appears to be erratic producing many different overtone pitches. What results are particular tone colors or timbres of instruments and voices.

23. Harmonic Pattern?

24. Standing Waves for a Pipe Open at BOTH ends Open at ONE end

25. Harmonic Example What are the first three harmonics in a 2.45 m long pipe that is open at both ends? What are the first three harmonics of the pipe when one end of the pipe is closed? Assume that the speed of sounds in air is 345 m/s for both of these situations. What are the first three harmonics in a 2.45 m long pipe that is open at both ends? What are the first three harmonics of the pipe when one end of the pipe is closed? Assume that the speed of sounds in air is 345 m/s for both of these situations.

26. “Timbre” (TAM-ber) is the specific property of sound that enables us to determine the difference between a piano and a harp.

27. Beats Interference of waves of slightly different frequencies traveling in the same direction, perceived as a variation in loudness. Interference of waves of slightly different frequencies traveling in the same direction, perceived as a variation in loudness.

28. Noise