SOUND and its properties.pptx

SOUND and its properties

1. Sound and its properties . SYED MASOOD

2. Sound Sound  is a  mechanical wave  that is an  oscillation  of  pressure  transmitted through a  solid ,  liquid , or  gas , composed of  frequencies  within the range of hearing and of a  level sufficiently strong  to be heard, or the sensation stimulated in organs of hearing by such vibrations.

3. Sound is a longitudinal wave propagating in an elastic medium The sound wave is pressure /medium motion oscillations Pressure and particle velocity are in phase in the propagating sound wave

4. Propagation of sound Sound is a sequence of waves of pressure which propagates through compressible media such as air or water. (Sound can propagate through solids as well, but there are additional modes of propagation). During their propagation, waves can be reflected, refracted, or attenuated by the medium.

5. The behavior of sound propagation is generally affected by three things: A relationship between density and pressure. This relationship, affected by temperature, determines the speed of sound within the medium. The propagation is also affected by the motion of the medium itself. For example, sound moving through wind. Independent of the motion of sound through the medium, if the medium is moving, the sound is further transported. The viscosity of the medium also affects the motion of sound waves. It determines the rate at which sound is attenuated. For many media, such as air or water, attenuation due to viscosity is negligible. However When sound is moving through a medium that does not have constant physical properties, it may be refracted (either dispersed or focused).

6. Sound reflection Sound reflection depends on the difference between the characteristic impedance of the medium on both sides of the boundary. Large impedance differences=large fraction of sound energy is reflected, small fraction is transmitted

7. Reflection Reflection from a soft-hard boundary Reflection from a hard-soft boundary

8. Temperature and velocity gradients An upward oriented velocity gradient (lower ground temperatures) produces downward deflection: A downward oriented gradient (higher ground temperatures) produces upward deflection

9. Sound diffraction Objects interact with the sound wave in the following ways: Objects that are smaller than 1/6th wavelength are ’transparent’ to sound Objects with sizes comparable to the wavelength scatter or diffract the sound wave Objects with sizes more than 5-10 wavelengths reflect the sound wave

10. Wind effects, attenuation The effect of wind currents is to bend the sound wave In addition to the drop of sound pressure due to spreading, sound can be absorbed/scattered by the medium Especially humidity effects on ultrasound

11. Temperature and wind effects Since sound velocity depends on temperature, c=331 + 0.6 T in air temperature gradients result in a velocity gradient. A velocity gradient produces refraction of the sound wave according to Snell’s law:

12. For humans, hearing is normally limited to frequencies between about 20  Hz  and 20,000 Hz (20  kHz ). The sound waves cause pressure changes against our ear drum sending nerve impulses to our brain. Perception of sound

13. Sound is made when something vibrates. The vibration disturbs the air around it. This makes changes in air pressure. These changes in air pressure move through the air as sound waves.

14. Physics of sound The mechanical vibrations that can be interpreted as sound are able to travel through all  forms of matter , gases ,  liquids ,  solids , and  plasmas . The matter that supports the sound is called the  medium . Sound cannot travel through a  vacuum 1 Longitudinal and transverse waves 2 Sound wave properties and characteristics 3 Speed of sound 5 Noise

15. Compressions The close together part of the wave Rarefactions The spread-out parts of a wave Wave particles vibrate back and forth along the path that the wave travel 1 Longitudinal and transverse waves Longitudinal or compression waves.

16. Transverse waves Crests Highest part of a wave Troughs The low points of the wave wave particles vibrate in an up-and-down motion .

17. Waves transfer energy without transferring matter. Frequency= waves/time

18. Properties of Sound

19. Frequency : the number of wave cycles/second (f). Wavelength : The distance (in m) between two wave maxima Phase : time offset of wave zero crossing compared to reference

20. Amplitude - is the maximum distance the particles in a wave vibrate from their rest positions. Wave Velocity - is the speed with which a wave crest passes by a particular point in space It is measured in meters/second. Wave Velocity = Frequency  Wavelength

21. The three components of sound are: Pitch (how high or low) Loudness (volume) Timbre (tone color)

22. Pitch The vibration patterns of some sounds are repetitive. Vibration patterns are also called waveforms. Each repetition of a waveform is called a cycle. We can hear frequencies between 20 hertz or cycles (vibrations) per second (low pitches)to 20 kilohertz, i.e. 20,000 Hz (high pitches).

23. When the frequency of a sound doubles we say that the pitch goes up an octave. We can hear a range of pitches of about ten octaves. Many animals can make sounds and hear frequencies that are beyond what we can hear.

24. Loudness To create vibrations energy is used. The greater amount of energy used the louder the sound. The strength of the changes in air pressure made by the vibrating object determines loudness.

25. As the sound spreads out from its source, the concentration of power becomes less. As the distance from the source increases the amount of power is spread over a greater area. The amount of power per square meter is called the intensity of the sound.

26. Loudness of Sound in Decibels Sound Loudness (dbs) Hearing Damage Average Home 40-50 Loud Music 90-100 After long exposure Rock Concert 115-120 Progressive Jet Engine 120-170 Pain

27. Ultrasound - sound waves with frequencies above the normal human range of hearing. Sounds in the range from 20-100kHz Infrasound - sounds with frequencies below the normal human range of hearing. Sounds in the 20-200 Hz range

28. “Timbre” (TAM- ber ) or tone color is the specific property of sound that enables us to determine the different types of sound produced.

29. Speed of Sound Medium velocity (m/s) air (20 C) 343 air (0 C) 331 water (25 C) 1493 sea water 1533 diamond 12000 iron 5130 copper 3560 glass 5640 The speed of sound depends on the medium the waves pass through, and is a fundamental property of the material .

30. Noise Noise is defined as “Sound or a sound that is loud, unpleasant, unexpected, or undesired.”

31. Interference the result of two or more sound waves overlapping

32. Different sounds that you hear include (A) noise, (B) pure tones, and (C) musical notes .

33. Doppler Effect is the apparent change in the frequency of a sound caused by the motion of either the listener or the source of the sound .

34. Doppler shift A moving sound source ’compress’ the sound waves in front of the object in the motion direction -Increased frequency Rarify the sound waves behind the object -Decreased frequency

35. Sounds from Moving Sources . A moving source of sound or a moving observer experiences an apparent shift of frequency called the Doppler Effect. If the source is moving as fast or faster than the speed of sound, the sound waves pile up into a shock wave called a sonic boom. A sonic boom sounds very much like the pressure wave from an explosion

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