Now there are a lot of opportunities on the Internet to test your hearing acuity online. To do this, you need to start a video with sound, the frequency of which is increasing. The creators of the test recommend testing with headphones so that extraneous noise does not interfere. The audio frequency range in the video starts with such high values that only a few can hear. Further, the frequency of the sound gradually decreases, and at the end of the video a sound is heard that even a person with hearing loss can hear.
During the video, the user is shown the value of the frequency of the sound that is being played. The test conditions suggest that the video must be stopped at the moment when a person can hear the sound. Next, you should see at what point the frequency stopped. Its value will make it clear that the hearing is normal, better than most people, or you should see a doctor. Some tests show what age is the cutoff frequency that a person could hear.
What is sound and sound wave
Sound is a subjective sensation, but we hear it because something real exists in our ear. This is a sound wave. Physicists are interested in how the sensations we experience are related to the characteristics of the sound wave.
Sound waves are longitudinal mechanical waves with a small amplitude, the frequency range of which is 20 Hz-20 kHz. Small amplitude is when the change in pressure due to compression-rarefaction is much less than the pressure in this medium. In air, in areas of compression-rarefaction, the change in pressure is much less than atmospheric pressure. If the amplitude is of the same order or greater than atmospheric pressure, then these are no longer sound waves, but shock waves, they propagate at supersonic speed.
Audience of sounds
We have already figured out what the range of audio frequencies is, but what lies beyond its borders? If the frequency is less than 20 Hz, such waves are called infrasonic. If more than 20 kHz - these are ultrasonic waves. Both infra- and ultrasound do not cause auditory sensations. The boundaries are quite blurred: babies hear 22-23 kHz, older people can perceive 21 kHz, someone hears 16 Hz. That is, the younger the person, the higher the frequency he can hear.
Dogs hear higher frequencies. This ability of theirs is used by trainers, they give commands to ultrasonica whistle that people can't hear. The figure shows the frequency ranges available for perception by different animals.
Sound like police guns
Let's give an example of a case that shows that the range of sound frequencies heard by a person is approximate and depends on individual characteristics.
In Washington, the police found a way to non-violent dispersal of youth. Boys and girls constantly gathered near one of the metro stations and talked. The authorities felt that their aimless pastime interferes with others, because too many people accumulate at the entrance. The police installed a Mosquito device that emitted a sound at a frequency of 17.5 kHz. This device is designed to repel insects, but the manufacturers assured that sound waves of this frequency are perceived only by teenagers from 13 and not older than 25.
Thanks to the device, the youth managed to get rid of, but a 28-year-old man heard a sound and complained to the city administration. Local authorities had to stop using the device.
Wavelength range
Sound frequency waves in different environments have different characteristics. The length and speed of propagation of the wave differ. In air (at room temperature) the speed is 340 m/s.
Consider waves with frequencies that are in the audible range for us. Their minimum length is 17 mm, the maximum is 17 m. The sound with the smallest wavelength is on the verge of ultrasound, and with the largest -approaching infrasound.
Sound wave speed
It is believed that light travels instantly, but it takes a certain time for sound to travel. In fact, light also has speed, it's just the limit, faster than light, nothing moves. As far as sound is concerned, its propagation in air is of greatest interest, although the speed of a sound wave in denser media is much higher. Consider a thunderstorm: first we see a flash of lightning, then we hear a roll of thunder. Sound is delayed because its speed is many times slower than the speed of light. For the first time, the speed of sound was measured by fixing the time interval between a musket shot and the sound. Then they took the distance between the tool and the researcher and divided it by the time of the "delay" of the sound.
This method has two drawbacks. Firstly, this is the error of the stopwatch, especially at a close distance to the sound source. Secondly, it is the speed of the reaction. With this measurement, the results will not be accurate. To calculate the speed, it is more convenient to take the known frequency of a particular sound. There is a frequency generator, a device with a range of audio frequencies from 20 Hz to 20 kHz.
It is turned on at the desired frequency, during the experiment the wavelength is measured. Multiplying both values, get the speed of sound.
Hypersonic
Wavelength is calculated by dividing speed by frequency, so as frequency increases, the wavelength decreases. It is possible to create oscillations of such a high frequency that the wavelength will be of the same order of magnitude as the wavelengthfree path of gas molecules, such as air. This is hypersound. It does not propagate well, because air is no longer considered a continuous medium, since the wavelength is negligible. Under normal conditions (at atmospheric pressure), the mean free path of molecules is 10-7 m. What is the range of wave frequencies? They are not sound, because we do not hear them. If we calculate the frequency of hypersound, it turns out that it is 3×109 Hz and higher. Hypersound is measured in gigahertz (1 GHz=1 billion Hz).
How the frequency of a sound affects its pitch
Audio frequency range affects pitch range. Although the pitch is a subjective sensation, it is determined by the objective characteristic of the sound, the frequency. High frequencies produce a high sound. Does the pitch of the sound depend on the wavelength? Of course, speed, frequency and wavelength are all related. However, the sound of the same frequency will have a different wavelength in different environments, but it will be perceived in the same way.
We hear sound because changes in pressure cause our eardrum to vibrate. The pressure changes with the same frequency, so it does not matter that the wavelength is different in different media. Due to the same frequency, we will perceive the sound as high or low, even in water, even in air. In water, the speed of sound is 1.5 km / s, which is almost 5 times greater than in air, therefore, the wavelength is much larger. But if the body vibrates at the same frequency (say, 500 Hz) in both environments, the pitch will be the same.
There are sounds that do not havepitch, for example, the sound "shhhhh". Their frequency fluctuations are not periodic, but chaotic, so we perceive them as noise.
