Is there a cap to the frequency of sound in the air? Why?

It's up to you how you define sound waves. Sound waves are mechanical waves that can theoretically be expressed in a variety of forms. Personally, I don't think that sound wave frequencies in the air can be considered strictly sound waves when they reach the thermodynamic range.

But theoretically, sound waves can also be explained in terms of thermodynamics, so the frequency limit of thermodynamics can also be used to define the limiting flatness of sound waves. Therefore, according to the thermodynamic definition, under the standard situation (temperature 20 degrees Celsius, relative humidity 0, pressure 1atm), in normal air (density, sound speed 343 meters per second), the frequency of the sound wave wavelength close to the molecular mean free path (68 nm) is about 5,04411765 10 to the 9th power Hz, which is about 500 MHz. At present, ultra-high frequency ultrasound waves that can be measured using RF technology (radio frequency) are about 50MHz.

If it is easier to define the limit of sound waves in terms of the characteristics of waves, for example, in the standard case (temperature 20 degrees Celsius, relative humidity 0, pressure of one atmosphere), normal air (density, a normal plane sound wave (high decibel shock wave is not counted as sound wave, spherical wave should consider diffusion) propagation distance of one wavelength, its energy loss of more than 50% should not be regarded as normal sound wave. In this way, the limit high frequency of sound waves is about 10MHz. The frequency range of sound propagating in the air is very wide, normal people can hear the sound from 20Hz to 20000Hz, while the high-frequency sound of the elderly is reduced to about 10000Hz (or can be as low as 6000Hz).

People call the sound with a frequency higher than 20,000 Hz ultrasound, and the sound below 20 Hz called infrasound. Ultrasonic waves (above 20,000 Hz) and normal sound waves (20 Hz - 20,000 Hz) will propagate in the opposite direction of the original propagation direction when they encounter obstacles, while some infrasound waves (below 20 Hz) can penetrate obstacles, and the infrasound waves generated by Russia's nuclear test in the Arctic Ocean once circled the earth six times. Ultra-low frequency infrasonic waves are more destructive to people than other sound waves (sound waves above 10Hz), and some of them can cause human blood vessels to rupture and cause death, but the generation conditions of this kind of sound waves are extremely harsh, and the probability of encountering them is very low.

The human vocal frequency is in the range of 100 Hz (bass) to 10,000 Hz (soprano). <>

The upper limit of sound frequency has not been studied, but in the case of solids, there is a gap between atoms, and there is an upper limit to the sound frequency of this gap alone. Let a bunch of atoms with a spacing of a wave form a vibration formation of a wave vector. If you let the wave vector be added, i.e., , then k'The vibration pattern given is exactly the same as that of K.

The blue line wave in the figure below is the wave formed by the wave vector, the red line is the wave formed by the wave vector, and the dots represent the actual atomic position. Note that in fact only the position of the point is visible, and the line is only drawn to assist. So, k'The vibration mode is not different from k, and the atomic positions given by the two wave vectors are exactly the same.

So as long as the wave vector is greater than , no new vibration mode will be given for the atom. The wave vector has a maximum value, which limits the minimum wavelength. For air, although the atoms are moving randomly, there are still gaps between molecules, and there should be no wavelength of infinite wavelength for this alone, so there should be an upper limit on the frequency of sound waves.

But in fact, I haven't checked how many of the most frequent sound waves can reach. <>

Grammatically speaking, there is nothing wrong with it. But logically wrong! The propagation of sound requires a medium, and the vibration of matter produces a source of sound waves, which cause various molecules in the air to vibrate and propagate to distant distances, and then there is no sound after the energy is consumed.

But there is a problem with saying that "air can also make sound", and it is difficult to determine who the source of the sound is. Ultrasound is produced by the vibration of an object. The number of vibrations per second is called the frequency of sound, and it is measured in hertz.

The frequency of sound waves that our human ears can hear is 20 to 20,000 Hz. Therefore, when the vibration of an object exceeds a certain frequency, that is, above the upper limit of the hearing threshold of the human ear, people cannot hear it, and such sound waves are called "ultrasound". Ultrasound, which is usually used for medical diagnosis, has a frequency of 1 5 MHz.

Ultrasonic waves have the characteristics of good directionality, strong penetrating ability, easy to obtain concentrated sound energy, and long propagation distance in water. It can be used for distance measurement, speed measurement, cleaning, welding, stone crushing, etc. <>

Of course there is a ceiling, because everything has a ceiling. If the volume exceeds the upper limit, then you will not be able to hear, because the frequency and upper limit of the sound heard are different for each age and species.

There is a limit to the size of the sound, and if it is exceeded, the sound can no longer be heard, and only some animals can hear the sound.

The sound is loud and small, but there is an upper limit to the sound, its highest back is 194 decibels, if you put it into such a loud sound, it will be very uncomfortable, I will not be able to stand it.

When people sing, they use muscles to pull the vocal cords, emitting many overtone components, with frequencies as high as 8-10kHz, through the action of the nasal cavity, they resonate with certain frequencies (including fundamental and overtone components) to make the sound brighter, their fundamental frequency range is: children's treble frequency range is 260-880hz, bass frequency range is 196-700hz, female voice treble frequency range is, bass frequency range is 200-700khz, The male voice has a treble frequency range of 160-523kHz and a bass frequency range of 80-358Hz.

The international communication standard is 300Hz-3400Hz!

When a person speaks, the fundamental frequency range is about 100 Hz to 300 Hz, with a lower male voice and a higher vocal tract and larynx for female and child voices. In the chorus, it is generally divided into four voices, and the vocal range (frequency range) of these four voices is: soprano 246 9hz 987 8hz, contralto 164 8hz 659 2hz, tenor 110hz 440hz, bass 73 4hz 293 7hz.

The lowest notes emitted by a deep bass can reach frequencies of 65 4Hz. The highest note emitted by the flowery soprano can reach a frequency of 1177 2Hz.

The vocal frequency range and auditory frequency range of humans and some animals.

Name: Vocal frequency range: δf hz, auditory frequency range: δf hz, person: 65, 1 100, 20, 20 000

Dogs 450 1 800 15 50 000 Cats 760 1 500 60 6 500

Bats 10 000 150 000 1 000 200 000 Dolphins 7 000 120 000 150 150 000 Robin 2 000 13 000 250 20 000 Fish 40 2 000

Because the frequency of the sound produced by the vibration of butterfly wings is less than 20Hz, it is an infrasound and a burning wave, so the human ear cannot hear the sound that our human ear can hear belongs to sound waves in the classification of sound waves; The frequency range is 20hz 20000hz, so the answer is: because the frequency of the butterfly wings vibrating to make the laughing sound is less than 20hz, it is an infrasound wave; Sound wave; 20hz～20000hz．

When people sing, they use muscles to pull the vocal cords, emitting many overtone components, with frequencies as high as 8-10kHz, through the action of the nasal cavity, they resonate with certain frequencies (including fundamental and overtone components) to make the sound brighter, their fundamental frequency range is: children's treble frequency range is 260-880hz, bass frequency range is 196-700hz, female voice treble frequency range is, bass frequency range is 200-700khz, The male voice has a treble frequency range of 160-523kHz and a bass frequency range of 80-358Hz.

The international communication standard is 300Hz-3400Hz!