Sound waves, affecting the human eardrum, cause vibrations of the hairs. The amplitude of these sound vibrations is directly related to the perceived loudness of these waves - the larger it is, the stronger the sound volume will be felt. This, of course, is a simplified interpretation. But the point is clear!
Each person will have his own perception of the same sound power. Therefore, it will be fair to say that loudness is a subjective quantity. In addition, this parameter depends on the frequency and amplitude of sound vibrations, as well as the pressure of the waves. Such factors as the duration of vibrations, their localization in space, timbre and spectral composition influence the sound volume.
The unit of sound volume is called sone. 1 dream approximately corresponds to the volume of a muffled conversation, and the volume of aircraft engines is equal to 264 sleeps. By definition, 1 dream is equal to the volume of a tone with a frequency of 1000 and a level of 40 dB. Sound power expressed in sons has the formula:
J = k * I 1/3 , here
k - frequency-dependent coefficient, i - vibration intensity.
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 background (phon) is also used to evaluate its strength. 1 is equal to the difference in volume levels of 2 sounds with the same frequency, for which sounds with the same volume frequency of 1000 Hz will differ in level of pressure (intensity) by 1 decibel.
In practice, in order to indicate or compare the volume, the decibel is most often used - a derivative of one from bel. This is due to the fact that the increase in sound power 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 amplitude of the oscillations. This is a fairly large unit. Therefore, for the calculations use its tenth - decibel.
During the day, the human ear can hear sound waves with a volume of 10 decibels or higher. It is believed that the maximum range of all frequencies available to humans is 20–20,000 Hz. It is noticed that it changes 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 (first kilohertz) are included in the area of speech communication. They are used in broadcasting on the DV and CB 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 fluctuations of 5-10 Hz can cause resonance with vibration of internal organs, affect the brain and increase aching pain in the joints and bones. But ultrasound is widely used in medicine. Also with its help, insects (midges, mosquitoes), animals (for example, dogs), birds from airfields are scared away.
To find out the volume of sound or noise, a special device is used - a noise level meter . It helps to find out if the sound vibrations do not exceed the maximum permissible 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. In this case, pathological disorders in the nervous and cardiovascular systems can also occur. Safe volume is limited to 35 dB. Therefore, to preserve hearing, you should not listen to music at full volume on the headphones. Being in a too noisy place, you can use ear plugs.