1. 9 Principles of sound 声学原理 The abilities of speaking and hearing are very important factors in our personal lives and in our environment. Areas such as music, sound recording and reproduction, noise control is also important. The main sources of environmental noise issues are transportation noise, industrial noise, industrial noise, construction noise and noise from leisure and entertainment. 波长 波长

2. Common topics of concern are 1 ） the exclusion of external noise 隔断外部噪声 1 ） the exclusion of external noise 隔断外部噪声 2) the reduction of sound passing between rooms and 减少房间之间的声音传递 2) the reduction of sound passing between rooms and 减少房间之间的声音传递 3) the quality of sound inside rooms 室内音质 3) the quality of sound inside rooms 室内音质

3. Before these topics are studied, this chapter outlines the basic principles of sound and its measurement. These basic principles are indicated below: 9.1 Nature of sound 声音的特性 9.2 Sound levels 声级 9.3 Attenuation of sound 声音的衰减 9.4 Nature of hearing 听觉特征

4. 9.1 Nature of sound what is sound ? Sound is a sensation produced in the ear and brain by variations in the pressure of the air. Sound is a Mechanical Wave. These pressure variations transfer energy from a source of vibration. What can be Origin of sound 声源 ? Moving objects: loudspeakers 扬声器, guitar strings 吉他弦, vibrating walls, and human vocal chords 人声. Moving air: horns 号角, organ pipes 管风琴, mechanical fans 风 机 and jet engines 喷气发动机. Vocal 声音的, 有声的, 歌唱的 Chord 弦, 和音, 情绪

5. The sound waves travel in a longitudinal 纵向的 type How do the sound waves travel? Its corresponding Transverse Waves 横波 左右分工小能人 ( 横波与纵波 )

6. Water Waves Water waves are an example of waves that involve a combination of both longitudinal and transverse

7. The sound waves can travel through solids, liquids and gases Sound is a mechanical wave and cannot travel through a vacuum. Light is an electromagnetic wave and can travel through the vacuum of outer space A vacuum?

8. It is convenient to represent the wave as follows plot （绘图） the vibrations against time. For a pure sound of one frequency ， the plot takes the form of a sine wave 正弦波. can be specified in terms of : Wavelength Frequency Velocity

9. How is the Velocity of sound? The velocity of sound is affected by the properties of the material through which it is traveling. The velocity in air increases as the temperature or humidity increases. An indication of the velocity of sound in different materials is given in table 9.1 P181 松树, 树木 5th row pine 松树, 树木 花岗岩 Last row granite 花岗岩

10. How is the Frequency of sound? If an object that produces sound waves vibrate 100 times a second, then the frequency of that sound wave will be ?? 音调 The human ear hears this as sound of a certain pitch 音调. Pitch Pitch is the frequency of a sound as perceived by human hear. Low-pitched notes are caused by low-frequency sound wave high-pitched notes are caused by high-frequency waves. 笔记, 短信, 音符 Note 笔记, 短信, 音符

11. 20 to 20, 000Hz The frequency range to which the human ear responds is approximately 20 to 20, 000Hz The range is too wide, what should we do? To divided it into several parts How to divide?

12. one method is one method is An octave band 倍频程 An octave band 倍频程 Octave bands commonly used in frequency analysis have the following centre frequencies. 31.5 63 125 250 500 1000 2000 4000 8000Hz 31.5 63 125 250 500 1000 2000 4000 8000Hz Octave 八个一组的物品, 八度音阶 中心频率 Hz 631252505001000200040008000 频率范围 Hz 45~ 90 90~ 180 180~ 355 355~ 710 710~ 1400 1400~ 2800 2800~5 600 5600~ 11200

13. How to describe the Quality of sound 音质 纯音 sound with only one frequency. pure tone 纯音 sound with more than one frequency. 440Hz = fundamental 基准音 or 1 st harmonic 谐音 880Hz = 1 st overtone 泛音 or 2 nd harmonic 1320Hz = 2 nd overtone or 3 rd harmonic etc. Overtones 泛音 harmonics 谐音 Overtones 泛音 and harmonics 谐音 are frequencies equal to whole-number multiples of the fundamental frequency

14. 音调的高低取决于基频，而音色取决于谐频分量的构成 Basic frequency 谐频 harmonics 880, 1320, 1760, 2200, 2640, 3080, 3520……

15. difference between pure tone, music and noise

16. When you sing in a bathroom, what would you find?

17. Resonance 声音的共鸣 Every object has a natural frequency depends on factors such as the shape, density and stiffness of the subject. Resonance occurs when the natural frequency of an object coincides with the frequency of any vibrations applied to the object. The result of resonance is extra large vibrations at this frequency.

18. 9.1 Nature of sound 9.2 how to measure sound? Sound power 声功率 Unit : watt 声源单位时间内向外辐射的声能 Sound intensity 声强 Unit: w/m 2 is the sound power distributed over unit area. 单位面积的声功率 - 单位时间单位面积所通过的声能 Sound pressure 声压 Unit: Pa is the average variation in atmospheric pressure caused by the sound 声音所引起的空气压强的平均变化量 Intensity –pressure relationship

19. I = 100 w/m 2 p =200 Pa Thresholds of pain 痛阈 is the strongest sound that the human ear can tolerate. If you want to detect a sound at 1000Hz, it’s sound intensity must be greater than I o = 1X10 -12 W/m 2 P o = 20X10 -6 Pa Thresholds of hearing 听阈 is the weakest sound the average human ear can detect.

20. What is Decibels ? 分贝 对数的 Decibels is a logarithmic 对数的 ratio of two quantities. Sound intensity level 声强级 Sound pressure level 声压级

21. Now, here is a question. A clock with a alarm of 60dB When there are two of such clocks, Ring at the same time, Do you think what the dB would be ?

22.  L = 3 dB Worked example 9.3 Calculate the change in sound level when the intensity of a sound is doubled. Let I=initial intensity, so 2I= final intensity Let L 1 =initial sound level and L 2 =final sound level Therefore: double the energy gives a 3 dB increase in sound level

23.  L = 3 dB double the energy gives a 3 dB increase in sound level decibels can be directly added? Intensities can be added decibels cannot be directly added? Sound pressure can be directly added?

24. 3dB increase in sound level is caused by doubling the sound energy 10 dB increase in sound level seems approximately twice as loud.  L = 3 dB

25. Worked example 8.4 Calculate the total sound level caused by the combination of sound levels of 95dB and 90dB. Threshold of hearing intensity =1X1 -12 W/m 2 Let I 1 =intensity of 95dB I 2 =intensity of 90dB and I 3 =intensity of the combined sounds Using

26. Please check the following website www.sengpielaudio.com/calculator www.sengpielaudio.com/calculator The addition of decibel values is made easier with the aid of a scale such as that shown in figure 9.7.

27. 3dB increase in sound level is caused by doubling the sound energy 10 dB increase in sound level seems approximately twice as loud.  L = 3 dB

28. 9.3 can sound be attenuated 衰减 as spread out from a source? 振幅 their amplitude 振幅 decreases and the sound level drops. does the total energy of the sound wave decrease a lot? Except for some absorption by the air, the total energy of the wave nearly remains constant but the area of the wave front constantly increases. The energy therefore spreads over larger areas and the density of this energy or the sound pressure measured at any point must decrease.

29. 9.3.1 How does a Point source attenuate? Inverse Square Law 平方反比定律 in inverse proportion to The sound intensity from a point source of sound decreases in inverse proportion to the square of the distance from the source.

30. Worked example 9.5 A microphone measures sound at a position in a free field 5m from a point source. Calculate the change in SPL if the microphone is moved to a position 10m from the source. Let L1=SPL at distance d1=5m L2=SPL at distance d2=10m Using The SPL decreases by 6 dB each time the distance is double from a point source of sound in free space. The SPL decreases by 6 dB each time the distance is double from a point source of sound in free space.

31. A roadway can be a line source of air and noise pollution and need not be a straight line.

32. 9.3.2 how does a Line source attenuate? The attenuation of sound from a line source in a free field can be shown by general relationship Sound intensity from a line source decreases in simple inverse proportion to the distance from the source. In free space

33. Figure 9.9 Attenuation of sound from a line source McMullan

34. 9.4 Nature of hearing 听觉特性 9.4.1 do you know your ear? can be divided into three main parts. 外耳 Outer ear 外耳 中耳 Middle ear 中耳 内耳 Inner ear 内耳

35. 9.4.2 longer exposure to noise, you may have deafness 耳聋 (1) Middle ear deafness 中耳耳聋 (2) Nerve deafness 神经性耳聋 Temporary threshold shift (TTS) 暂时性失聪 Temporary threshold shift (TTS) 暂时性失聪 is a temporary loss of hearing which recovers in 1-2 days after the exposure to noise. Permanent threshold shift (PTS) 永久性失聪 Permanent threshold shift (PTS) 永久性失聪 is a permanent loss of hearing caused by longer exposure to noise.

36. 9.4.4 how to judge the Loudness of a sound ？ 响度 a 50Hz tone at 70dB a 50Hz tone at 85dB a 50Hz tone at 78dB a 1000Hz tone at 60dB a 200Hz tone at 60dB As the intensity of a sound increases it is heard to be “louder”. Which one is heard to be louder?

37. It can be seen that the ear is most sensitive in the frequency range between 2~5kHz, and least sensitive at low frequencies or at extremely high frequencies.

38. The unit of loudness a 50Hz tone at 78dB a 1000Hz tone at 60dB a 200Hz tone at 60dB Their loudness are 60 phone Another unit: 重编号 sone is a renumbering 重编号 of the phone scale so that sone values are directly proportional to the magnitude of the loudness. One sone is equivalent to 40 phons. 2 sones is twice as loud as 1 sone. Sone is doubled each time the loudness level is increased by 10 phons A sound with 60 phone is twice as loud as 30 phone?

39. Exercises in class 1 The sound waves can travel through （ ） solids, liquids and gases A solids B liquids C gases D a vacuum

40. 2 The frequency range to which the human ear responds is approximately ( ) A 20 to 2,000Hz B 20 to 20, 000Hz C 200 to 2,000Hz D 200 to 20,000Hz

41. 3 double the energy gives a （ ） increase in sound level A 3 dB B 10 phones C 6 dB D 10 dB

42. 4 （ ） increase in sound level seems approximately twice as loud. A 3 dB B 10 phones C 6 dB D 10 dB

43. 5 The SPL decreases by （ ） each time the distance is double from a point source of sound in free space. A 3 dB B 10 phones C 6 dB D 10 dB

44. 6 Sone is doubled each time the loudness level is increased by ( ) A 3 dB B 10 phones C 6 dB D 10 dB