The blue whale, the largest living animal, makes a sound that is much louder than the noise of a launching rocket. Such a loudness a person cannot bear. There is even a noise weapon. Its volume is only slightly louder than the whale's voice.
What determines the volume of the sound? Why can intense and low sounds hurt and even be deadly, while high ones can't? Why are low sounds heard at a greater distance than high ones? The article will answer these questions.
What determines the volume of the sound
This value depends on the sound frequency and wavelength, on the acoustic pressure and energy of the sound stream. But first things first.
What determines the volume of the sound? Physics has long known that loudness is determined by the characteristics of the wave. The faster the sound source vibrates, the higherthe frequency of the wave and the shorter its length. We call high-frequency sounds quiet, we perceive them as subtle. We can hear only at a short distance due to the small wavelength. Low frequency sounds are considered rough, perceived as loud, and can be heard from far away.
Acoustic pressure and sound flow
What determines the volume of the sound? In addition to the characteristics of the wave, from the acoustic pressure. This pressure is greater than atmospheric pressure, it generates a vibrating body. If the sound source moves with a large amplitude, low frequency, the pressure increases greatly.
The pressure creates the energy of the sound stream. This value is measured in W / m2 and shows how much kinetic energy passes through the surface in 1 second. The higher the pressure, the more intense the flow.
Sound volume and energy
To the question of what the loudness of sound depends on, physics gives the answer: from the flow of sound energy. Suppose the energy has increased 10 times - the volume will increase by one bel (1 b). Bel is a unit of loudness, however, for convenience and accuracy of measurements, it was decided to use decibels (1 dB=0.1 b).
Denote the initial sound energy as E0. If it increases 10 times and equals 10 E0 , then the volume will increase by 10 dB, if 100 times - by 20 dB, etc. Fluctuations in sound energy that the human ear can perceive have limits. Their range is change in 10trillion times, volume change - 130 dB. Minimum sound energy level E0=10-12 W/m2. Not everyone can hear such a weak sound, but only a person with a very developed hearing. It is with the value of E0 that all sounds are compared to characterize them as quiet or loud.
For clarity, let's give examples of the most common sounds, compare their volume and the energy of the sound stream. It is understood that sounds are perceived by a person from a distance of several meters.
| Type of sound | Sound volume (db) | Sound energy (W/m2) |
| leaf rustling | 10 | 10-11 |
| clock ticking | 20 | 10-10 |
| calm conversation | 40 | 10-8 |
| loud talk | 70 | 10-5 |
| noisy street | 90 | 10-3 |
| subway train | 100 | 10-2 |
Inaudible sounds and pain threshold
What determines the volume of the sound? In addition to everything that has already been considered, from the threshold of hearing. The sound can be arbitrarily loud (for other living beings or special devices), but if its frequency is less than 16-20 Hz (infrasound) and more than 16-20 kHz (ultrasound), then we will not perceive it.
Although we do not hear infrasound and ultrasound,they affect a person in different ways. Infrasound with a loudness of 75 dB is harmful to he alth, 120 dB is the pain threshold of a person, and a sound of 180 dB leads to death. This effect is explained by the fact that low frequencies of infrasound increase the pressure too much. Ultrasound is not dangerous, it is widely used in medicine, various industries, construction.
