Intensity and decibel scale
![intensity and decibel scale intensity and decibel scale](https://wordlesstech.com/wp-content/uploads/2019/07/Decibel-Scale-and-Noise-Level-Chart-2.jpg)
The outer ear acts much like a funnel, collecting the sound and transferring it inside the head down a passage that's about 3 cm long, ending at the ear drum. The ear is split into three sections, the outer ear, the middle ear, and the inner ear. The human ear is really quite an amazing detector of sound, and it's worth spending some time learning how it works. The decibel scale is used because it closely corresponds to how we perceive the loudness of sounds. This is 31.6 times as much as the original intensity. Taking the inverse log of 7.5 means simply raising 10 to the 7.5 power, so: Therefore, I / Io = the inverse log of 7.5. If this is increased to 75 dB, the new intensity can be found like this: The intensity in dB can be found by simply applying the equation: What is this in decibels? If the intensity is increased by 15 dB, what is the new intensity in W / m 2? A change by 1 dB is about the smallest change a human being can detect.Ī particular sound has an intensity of 1 x 10 -6 W / m 2. We perceive loudness to be doubled when the intensity increases by a factor of 10! This corresponds to a 10 dB increase. This does not correspond to a perceived doubling of loudness, however. On the decibel scale, doubling the intensity corresponds to an increase of 3 dB. The ear responds to the loudness of sound logarithmically, so the decibel scale is a logarithmic scale: A more convenient way to measure the loudness of sound is in decibels (dB) in decibels, the range of human hearing goes from 0 dB to 120 dB. The human ear has an incredibly large range, being able to detect sound intensities from 1 x 10 -12 W / m 2 to 1 W / m 2. This dependence on 1/r 2 applies to anything emitted uniformly in all directions (sound, light, etc.). At a distance r away from a source sending out sound with a power P, the sound passes through a sphere with a surface area equal to. In fact, the intensity is inversely proportional to the square of the distance from the source. If sound moves away from a source uniformly in all directions, the intensity decreases the further away from the source you are. Sound that is 1 W / m 2 is intense enough to damage the ear. The smallest detectable sound intensity, known as the threshold of hearing, is about 1 x 10 -12 W / m 2. The human ear can detect sound of very low intensity.
![intensity and decibel scale intensity and decibel scale](https://image.freepik.com/free-vector/decibel-scale-sound-level-graph_79145-234.jpg)
A sound wave is usually characterized by the power (energy / second) it carries: the intensity is the power (P) divided by the area (A) the sound power passes through: Just as the total energy in an oscillating spring is proportional to the square of the amplitude of the oscillation, the energy in a sound wave is proportional to the square of the amplitude of the pressure difference. In liquids, the speed of sound is more like 1000 m/s, and in a typical solid more like 5000 m/s. In air at 0 ☌, the speed of sound is 331 m/s. The speed of sound also depends on density, and is given by:įor an ideal gas, it turns out that the speed of sound is given by: The compressibility of a material is measured by the bulk modulus, discussed in chapter 9. In easily-compressible media, such as most gases, the speed of sound is slower because particles respond more slowly to motion of neighboring particles. Sound travels fastest in media which are hard to compress (like different metals) because if one particle moves in response to a pressure wave, its neighbor will respond quickly. The speed of sound thus depends on how easily a medium can be compressed (or, equivalently, expanded). A sound wave propagates by alternately compressing and expanding the medium.