Blue whale - the largest living animal, makes a sound that is much louder than the noise of a launching rocket. A person cannot endure such a loudness. There is even a noise weapon. Its volume is only slightly stronger than the voice of a whale.
What determines the sound volume? Why can intense and low sounds hurt and even be deadly, and high sounds not? Why are low sounds heard at a greater distance than high? The answers to these questions will give the article.
What determines the sound volume
This value depends on the frequency of sound and wavelength, on acoustic pressure and energy of the sound stream. But first things first.
What determines the sound volume? Physics has long known that volume is determined by the characteristics of a wave. The faster the sound source oscillates , the higher the frequency of the wave and the smaller its length. We call high-frequency sounds quiet, we perceive them as subtle. We can hear only at a short distance due to the short wavelength. Sounds of low frequency are considered rude, perceived as loud, they can be heard from afar.
Sound pressure and sound flow
What determines the sound volume? In addition to the characteristics of the wave, from acoustic pressure. This pressure, which exceeds atmospheric pressure, is generated by an oscillating body. If the sound source moves with a large amplitude, low frequency, the pressure increases greatly.
Pressure creates the energy of a sound stream. This value is measured in W / m 2 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 its energy
To the question of what the sound volume depends on, physics gives an answer: from the flow of sound energy. Suppose the energy has increased 10 times - the volume will increase by one white (1 b). Bel is a unit of measurement for volume, but for convenience and accuracy, it was decided to use decibels (1 dB = 0.1 b).
Denote the initial sound energy as E 0 . If it increases by 10 times and 10 will be equal to E0, the volume increased by 10 dB if 100 times -.. 20 dB, etc. The oscillations of sound energy, which the human ear is able to perceive have borders. Their range is a change of 10 trillion times, a change in volume - 130 dB. The minimum level of sound energy E 0 = 10-12 W / m 2 . Not everyone can hear such a weak sound, but only a person with a very developed hearing. It is with the value of E 0 that all sounds are compared in order to characterize them as quiet or loud.
For clarity, we give examples of the most common sounds, compare their volume and the magnitude of the energy of the sound stream. It is understood that sounds are perceived by a person from a distance of several meters.
Comparison table of volume and energy of different sounds| Kind of sound | Sound volume (db) | Sound stream energy (W / m 2 ) |
| rustling foliage | 10 | 10-11 |
| clock ticking | 20 | 10-10 |
| calm conversation | 40 | 10 -8 |
| loud conversation | 70 | 10 -5 |
| noisy street | 90 | 10 -3 |
| subway train | 100 | 10 -2 |
Inaudible sounds and pain threshold
What determines the sound volume? In addition to everything that has already been considered, from the threshold of audibility. The sound can be arbitrarily loud (for other living things 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 or ultrasound, they affect a person in different ways. Infrasound with a volume of 75 dB is harmful to health, 120 dB is the pain threshold of a person, and the sound of 180 dB leads to death. This effect is explained by the fact that low infrasound frequencies increase pressure too much. Ultrasound is not dangerous; it is widely used in medicine, various industries, and construction.