"Hazards and Control of Noise" PPT courseware download on acoustic phenomena

"Hazards and Control of Noise" PPT courseware download on acoustic phenomena

Part One: Guidance Design

Learning Point 1: Noise and its sources

Experiment 1: Use a knife to scrape back and forth on the glass and hear an annoying sound. Connect the microphone to the input end of the oscilloscope so that the sound from the glass is displayed on the oscilloscope through the microphone. The waveform is shown in Figure 2- As shown in 4-3A;

Figure B shows the waveform of the musical sound. Compare the two.

Experiment 2: Use a tape recorder to suddenly play a cheerful song with a loud voice to the students in the classroom.

Question 1: Why does the sound of the knife scraping the glass in Experiment 1 sound disturbing? What characteristics can be seen in the waveform of this sound wave from an oscilloscope?

Answer: Because the sound made by the knife when scraping the glass is very harsh and sharp, which makes people sound upset. The waveform of this sound is jagged and messy, indicating that the vibration of the knife when scraping the glass is messy and has a high frequency.

Question 2: Could the music in life be noise?

Answer: From the perspective of environmental protection, any sound that hinders people's normal rest, study and work, as well as any sound that interferes with the sounds people want to listen to, is noise. Of course, the music in life can also become noise.

Learning point 2: Noise intensity levels and hazards

Question: The intensity of sound is expressed in decibels (dB); 0 dB is the weakest sound that a person can hear just now; in order to ensure rest and sleep, the sound should not exceed 50 dB; in order to ensure work and study, the sound should not exceed 70 dB ;To protect hearing, the sound cannot exceed 90 dB.

Learning point 3: Control noise

Experiment: Wind up an alarm clock and do the following experiments: (1) Place it next to you to ring; (2) Place it in a closed box to ring; (3) Place it in the next room with closed doors and windows; ( 4) After plugging your ears with cotton balls, let it ring.

think:

Question 1: What are the differences between the sounds heard in experiments (2), (3), and (4) compared with those in experiment (1)?

Answer: The sounds heard in experiments (2), (3), and (4) were smaller than those in experiment (1).

Question 2: What does this experiment teach us about controlling noise?

Answer: From this experiment, we can know that to control noise, we can start from the sound source, the propagation process and the human ear.

Question 3: As shown in Figure 2-4-4, Figure A is to reduce noise from ______; Figure B is to reduce noise from ___________; Figure C is to reduce noise from ______.

Noise hazards and control PPT, Part 2: Application examples

Type 1: Discrimination of noise and music

Example 1 Regarding music and noise, which of the following is correct ()

A． The deafening chants of fans during football matches are noise

B. The melodious singing is beautiful and must be music.

C. In some cases, musical tones can also become noise

D. All noise must be loud

[ Analysis Singing is also noise for people who want to take a rest; but during football matches, the deafening shouts of fans are an act of excitement, not noise. The vibration of music follows certain rules, while the vibration of noise is chaotic and irregular; not all noises are necessarily loud. In summary, option C is correct.

[Error-prone analysis]There are two perspectives for classifying noise: the physics perspective and the environmental protection perspective. From an environmental protection perspective, beautiful and melodious music can also be considered noise under certain circumstances (such as late at night).

Type 2: Noise intensity levels and hazards

Example 2: One day, Xiao Ming saw the noise monitoring equipment on the street. If the display screen of the device displayed the data of 90 at a certain moment, the unit of this data is ________. When there are no cars or motorcycles passing nearby, he finds that the data on the display will ________ (optional "increase" or "decrease"). After returning home, he checked the physics information and learned that ______ is the weakest sound that people can hear just now; in order to protect hearing, the noise should be controlled not to exceed _______; in order to ensure work and study, the noise should be controlled not to exceed _______ ________; To ensure rest and sleep, the sound should not exceed ________.

[Error-prone warning]0 dB is the weakest sound that people can hear, which is the lower limit of hearing of the human ear. However, it does not mean that 0 dB means there is no sound. For example, infrasound waves are also sounds, but people My ears can't feel it.

Type 3: Ways to control noise

Example 3: The students had fallen asleep at night, but the night market outside the school was still open. The sound of hawking woke up some students. A angrily got up and closed the window, B was lazy and just covered his head with a blanket and went back to sleep. C simply got up and walked to the window, stuck his head out of the window and shouted "Stop making noise". The methods they adopt to reduce noise are: A: _______________; B: _______________; C: _______________.

[ Summary of rules] To control and reduce noise, measures are mainly taken from three aspects: noise elimination, sound insulation and sound absorption. There are three ways to reduce noise, namely attenuation at the sound source, attenuation during propagation, and attenuation at the human ear.

Noise hazards and control PPT, part 3: classroom feedback

1. As shown in Figure 8-1, A, B, C, and D are the waveform diagrams of four sounds. From the diagram, we can know which picture the waveform of the noise is ()

2. Which of the following statements about music and noise is correct ( )

A． Music is the sound produced by musical instruments, noise is the sound produced by machinery

B. Good singing sounds pleasant to the ears and makes people feel happy. It must not be noise.

C. From the perspective of environmental protection, all sounds that hinder people from studying, resting and working are noise.

D. Noise is the sound emitted when an object vibrates regularly

3． When Xiaohua was repairing the kitchen table at home, there were constant sounds of knocking objects. In order to avoid disturbing Xiaoming's study next door, Xiaohua adopted three solutions: ① place a rag on the place where the knock was made; ② put a The doors and windows of the room and kitchen are closed; ③Instruct Xiao Ming to temporarily plug his ears with headphones. Among the above three solutions, the first is to reduce the noise at _________, the second is to reduce the noise at _____________, and the third is to reduce the noise at _________.

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