Sound waves, affecting the human eardrum, cause the hairs to vibrate. The amplitude of these sound vibrations is directly related to the perceived loudness of these waves - the larger it is, the louder the sound will be felt. This is, of course, a simplified interpretation. But the point is clear!
The perception of the same sound power will be different for each person. Therefore, it is fair to say that loudness is a subjective value. In addition, this parameter depends on the frequency and amplitude of sound vibrations, as well as the pressure of the waves. The loudness of the sound is influenced by such factors as the duration of oscillations, their localization in space, timbre and spectral composition.
The unit of sound volume is called sleep (sone). 1 son is about the volume of a muffled conversation, and the volume of an airplane's engines is 264 sons. By definition, 1 sone is equal to the loudness of a tone with a frequency of 1000 and a level of 40 dB. The strength of sound, expressed in sons, has the formula:
J=kI1/3, here
к – frequency dependent coefficient, i – intensityhesitation.
Due to the fact that vibrations with different sound pressure (different in intensity) at different frequencies can have the same sound volume, a unit such as phon (phon) is also used to assess its strength. 1 Ф is equal to the difference in volume levels of 2 sounds with the same frequency, for which sounds of the same volume with a frequency of 1000 Hz will differ in pressure (intensity) by 1 decibel.
In practice, in order to indicate or compare loudness, the decibel, the derivative of the bel, is most often used. This is due to the fact that the increase in sound intensity does not occur in a linear dependence on the intensity of the waves, but in a logarithmic one. 1 bel is equal to a tenfold change in the strength of the oscillation amplitude. This is a fairly large unit. Therefore, for calculations, they use its tenth part - decibel.
Daytime, the human ear can hear sound waves of 10 decibels or more. It is generally accepted that the maximum range of all frequencies available to humans is 20–20,000 Hz. It has been observed to change with age. In youth, mid-frequency waves (about 3 kHz) are best heard, in adulthood - frequencies from 2 to 3 kHz, and in old age - sound at 1 kHz. Sound waves with an amplitude of up to 1-3 kHz (the first kilohertz) enter the zone of speech communication. They are used in broadcasting on the LW and MW bands, as well as in telephones.
If the frequency is less than 16-20 Hz, then such noise is considered infrasound, and if it is more than 20 kHz -ultrasound. Infrasound with oscillations of 5-10 Hz can cause resonance with the vibration of internal organs, affect the functioning of the brain and increase aching pain in the joints and bones. But ultrasound has found wide application in medicine. Also, with its help, insects (midges, mosquitoes), animals (for example, dogs), birds from airfields are repelled.
To find out the volume of sound or noise, a special device is used - a noise level meter. It helps to find out whether sound vibrations exceed the maximum allowable value, which does not pose a danger to humans. If a person is exposed to waves with a level exceeding 80-90 dB for a long time, this can cause complete or partial hearing loss. At the same time, pathological disorders in the nervous and cardiovascular systems can also occur. Safe volume is limited to 35 dB. Therefore, to preserve your hearing, you should not listen to music at full volume with headphones. If you are in a noisy place, you can use earplugs.
