It may be the most understandable voice interpretation of the vernacular! (under)
Good classmates, we started class. In the last lesson, we talked about three points: sound frequency, decibel, ambient noise, and answering a question: “The sound of the sound from the sound source must be heard when the decibel exceeds the ambient noise. To", (the portal of the last class) Today we talk about another point of knowledge - the spread of sound. How is the sound spread? The direction of the sound?
Knowledge goal:
1: know that the sound is generated by the vibration of the object;
2: know that sound can be transmitted through air, liquid and solid;
3: Know that the speed of sound propagation in different media is different;
4: It is known that the direction of transmission of audible and ultrasonic waves is different.
How is the sound spread?
The sound is generated by the vibration of the object. This vibration is called a wave, that is, a sound wave. When the sound wave encounters an object, it will cause the object to vibrate. Sound waves are perceived by the human or animal auditory organs during the propagation of the medium, which is the sound.
The reason why people can hear the sound is that when the sound wave emitted by the sound source object propagates in the air, it causes the vibration of the human eardrum. After the conversion of the human auditory organ, it finally becomes the sound that the human ear can hear.
So there are three conditions for the spread of sound:
1: vibration vibration of the sound source;
2: medium;
3: The perception of our ears
1: vibration of the object
That is, the sound source must be vibrated, such as breaking glass, birds, thunder, and voice. . .
2: Media
Usually because people live in the air, the medium that transmits sound is generally air, but in addition to air, sound can travel through liquids and solids.
The phenomenon of liquid sound is very common. When we swim in the swimming pool, we can hear the voice of the people on the shore under the water, and when we are fishing, we must keep quiet and not speak, afraid that the voice will scare away the fish. This means that water can spread sound.
An example of solid sound transmission - should we have played this next game when we were young?
Earth phone
Since the sound can propagate in different media such as air, liquid, solid, etc., when the sound wave encounters an obstacle (media conversion) while traveling, it cannot pass through and returns to the original medium, which is called reflection.
Acoustic reflection
3: The perception of our ears
The sound is transmitted to the ear through the air in the form of sound waves, causing the vibration of the ear tympanic membrane. This vibration is transmitted to the auditory nerve through the small bone and other tissues. The auditory nerve transmits the signal to the brain, and the brain obtains a sense of hearing according to the analysis.
Some unfortunate people have a natural hearing system damage, or the acquired accidents lead to hearing dysfunction, which is a problem in the process of receiving sound waves and analyzing sound waves.
So summed up: sound source + medium + perception, is the three elements we hear the sound. But in fact, the sound we can hear is only a small part, some are high-frequency low-frequency sound waves that are inaudible to the human ear, and some are weak when received by the human ear, but we are all airtight. Surrounded by various sound fields.
Solve how the sound spreads. Let's look at another question, the direction of the sound.
The direction of the sound?
I believe that everyone has this intuitive experience, and the voice is spread in all directions.
Indeed, because the sound is transmitted through the air, and the air is everywhere in our way. (Because people live in the air, here is a rough discussion of the direction in which sound travels in the medium of air.)
Again, the sound is transmitted by the motion of the sound wave. Finally, the human ear receives not the sound source itself, but the vibration, that is to say, there is no material migration in this process, and some are only the transmission of momentum (vibration).
Just like, if I hear the bird on the tree, what I hear is actually the vibration of the air caused by the sound of the bird. The vibration is transmitted to my ear and received, but the bird is still on the tree and does not move.
Because the air is nowhere in all directions, the vibration of the sound source body is transmitted by all the air in all directions, so that the sound is spread in all directions. This kind of transmission is like a bubble bubble that gradually blows up...
As we mentioned last time, the sound of audible sound waves (frequency between 20 Hz and 20 kHz) can be recognized by the human ear. In addition to audible sound waves, there are ultrasonic waves, infrasound waves...
Does ultrasound also follow this direction of propagation?
The direction of propagation of the ultrasound,
There is another concept here - diffraction, which refers to the physical phenomenon that the wave deviates from the original straight line when it encounters an obstacle.
The longer the wavelength, the more easily the diffraction occurs, and the wavelength is inversely proportional to the frequency of the wave. Therefore, the wavelength of the ultrasonic wave is short, it is not easy to diffract, and it is basically capable of directing linear propagation in a uniform medium.
Therefore, the ultrasonic waves are directional propagating.
Summarize the knowledge points of this lesson: (knocking on the blackboard)
1: know that the sound is generated by the vibration of the object;
2: know that sound can be transmitted through air, liquid and solid;
3: Know that the speed of sound propagation in different media is different;
4: It is known that audible sound is transmitted in all directions in the air, and ultrasonic waves are transmitted in a straight line.
PS: Everyone who has doubts about the voice can comment on your question. We have the top acoustic research experts from China to answer your questions~~~比心~~~
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