Values for γ for various gases are given in many physics textbooks and reference works. Here p is the equilibrium pressure of the gas in pascals, ρ is its equilibrium density in kilograms per cubic metre at pressure p, θ is absolute temperature in kelvins, R is the gas constant per mole, M is the molecular weight of the gas, and γ is the ratio of the specific heat at a constant pressure to the specific heat at a constant volume, Using the appropriate gas laws, wave velocity can be calculated in two ways, in relation to pressure or in relation to temperature: or Compressibility ( K) is the reciprocal of the bulk modulus ( B), as in In gas mediums this equation is modified to where K is the compressibility of the gas. Here ρ is the density and B the bulk modulus (the ratio of the applied pressure to the change in volume per unit volume of the medium). The speed of sound In gasesįor longitudinal waves such as sound, wave velocity is in general given as the square root of the ratio of the elastic modulus of the medium (that is, the ability of the medium to be compressed by an external force) to its density: Sound levels for audio systems, architectural acoustics, and other industrial applications are most often quoted in decibels. Sound levels for nonlinear (decibel) and linear (intensity) scalesĪrtillery fire at close proximity (threshold of pain)Īverage street noise loud telephone bellĪlthough the decibel scale is nonlinear, it is directly measurable, and sound-level meters are available for that purpose. (Sometimes the threshold of pain is given as 120 decibels, or 1 watt per square metre.) When the defining level of 0 decibel (10 -12 watt per square metre) is taken to be at the threshold of hearing for a sound wave with a frequency of 1,000 hertz, then 130 decibels (10 watts per square metre) corresponds to the threshold of feeling, or the threshold of pain. The correlation between the absolute intensity of a sound wave and its decibel level is shown in Table 1, along with examples of sounds at each level. Thus, an increase in absolute intensity from 10 -12 to 10 -11 watt per square metre corresponds to an increase of 10 decibels, as does an increase from 10 -1 to 1 watt per square metre. Because the decibel scale mirrors the function of the ear more accurately than a linear scale, it has several advantages in practical use these are discussed in Hearing, below.Ī fundamental feature of this type of logarithmic scale is that each unit of increase in the decibel scale corresponds to an increase in absolute intensity by a constant multiplicative factor. The reference intensity I 0, corresponding to a level of 0 decibels, is approximately the intensity of a wave of 1,000 hertz frequency at the threshold of hearing-about 10 -12 watt per square metre. Here L represents decibels, which correspond to an arbitrary sound wave of intensity I, measured in watts per square metre. Such a scale is provided by the sound intensity level, or decibel level, of a sound wave, which is defined by the equation Because of the enormous nonlinearity of the ear in sensing pressure waves, a nonlinear scale is convenient in describing the intensity of sound waves. The ear mechanism is able to respond to both very small and very large pressure waves by virtue of being nonlinear that is, it responds much more efficiently to sounds of very small amplitude than to sounds of very large amplitude. SpaceNext50 Britannica presents SpaceNext50, From the race to the Moon to space stewardship, we explore a wide range of subjects that feed our curiosity about space!.Learn about the major environmental problems facing our planet and what can be done about them! Saving Earth Britannica Presents Earth’s To-Do List for the 21st Century.100 Women Britannica celebrates the centennial of the Nineteenth Amendment, highlighting suffragists and history-making politicians.COVID-19 Portal While this global health crisis continues to evolve, it can be useful to look to past pandemics to better understand how to respond today.Student Portal Britannica is the ultimate student resource for key school subjects like history, government, literature, and more.This Time in History In these videos, find out what happened this month (or any month!) in history.#WTFact Videos In #WTFact Britannica shares some of the most bizarre facts we can find.Demystified Videos In Demystified, Britannica has all the answers to your burning questions.Britannica Classics Check out these retro videos from Encyclopedia Britannica’s archives.Britannica Explains In these videos, Britannica explains a variety of topics and answers frequently asked questions.
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