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This calculation shows the speed of sound in humid air according to Owen Cramer, "JASA, 93, p. 2510, 1993", with saturation vapor pressure taken from Richard S. Davis, "Metrologia, 29, p. 67, 1992", and a mole fraction of carbon dioxide of 0.0004. The calculator is valid over the temperature range 0 to 30° C (273.15 - 303.15 K) and over the pressure range 75 to 102 kPa. In the region between the air pressures 95.000 und 104.000 kPa there is no noticeable changing of the speed of sound c. The standard airpressure is 101325 Pa = 101.325 kPa or 1013.25 hectopascal. |
| The speed of sound in air is determined by the air itself and is not dependent upon the amplitude, frequency, or wavelength of the sound. For an ideal gas the speed of sound depends only on the temperature and is independent of gas pressure. This dependence also applies to air, in good approximation and can be regarded as an ideal gas. |
| Notice: The speed of sound changes clearly with temperature, a little bit with humidity − but not with air pressure (atmospheric pressure). The words "sound pressure at sea level" are incorrect and misleading. The temperature indication, however, is absolutely necessary. |
| Google is not correct (look at the following link)
http://www.google.com/search?q=speed+of+sound Here is the answer of Google: "Speed of sound at sea level = 340.29 m/s". This is not a good answer, because they forgot to tell us the temperature, and the given atmospheric pressure "at sea level" makes really no sense. |
| Reason: The air pressure p and density ρ of the air at the same temperature are proportional to each other. The ratio p / ρ is always constant, on a high mountain or even at sea level. Forget the atmospheric pressure, but make sure the important temperature. |
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Adiabatic index or ratio of specific heats κ (kappa) = cp / cv.
κ = 1.67 for monatomic molecules, 1.40 für diatomic molecules and 1.33 for triatomic molecules.
In SI units with dry air at 20 °C (68 °F), the speed of sound c is 343 m/s.
This also equates to 1235 km/h, 767 mph, 1125 ft/s.
Notice: Air density ρ is not the same as air pressure p0.
Statement: Speed of sound - temperature matters, not air pressure
Calculation: Speed of sound c in air and the important temperature
| The speed of sound is called Mach 1 Mach is commonly used to represent an object's speed, such as an aircraft or a missile, when it is travelling at the speed of sound or at multiples of it. |
| Mach Number below 1 means the flow velocity is lower than the speed of sound - and the speed is subsonic. Mach Number 1 means the flow velocity is the speed of sound - and the speed is transonic. Mach Number above 1 means the flow velocity is higher than the speed of sound - and the speed is supersonic. |
Air Density Calculations
First, consider the ideal gas law:
(1) p × V = n × R × T
| p = pressure, pascals (multiply mb by 100 to get pascals) |
| V = volume in m3 |
| n = number of moles |
| R = gas constant |
| T = temperature K = °C + 273.15 |
Density D = ρ is the number of molecules of the ideal gas in a certain volume.
In this case a molar volume, which can be mathematically expressed as:
(2) D = ρ = n / V
| D = ρ = density in kg/m3 |
| n = number of molecules |
| V = volume in m3 |
By combining the previous two equations, the expression for the density D = ρ becomes:
(3) 
| D = ρ = density in kg/m3 |
| p = pressure, pascals (multiply mb by 100 to get pascals) |
| R = gas constant = 287.05 J / (kg · K) for dry air |
| T = temperature K = °C + 273.15 |
As an example, using the standard sea level conditions of P = 101325 Pa and T = 15 °C,
the air density at sea level, can be calculated as:
D = ρ = 101325 / (287.05 × (15 + 273.15)) = 1.2250 kg/m3
This example has been derived for the dry air of the standard conditions. For real-world situations,
it is necessary to understand how the density is affected by the moisture in the air.
The density D = ρ of a mixture of dry air molecules and water vapor molecules can be expressed as:
(4) 
| D = ρ = density in kg/m3 |
| pd = pressure of dry air in pascals |
| pv = pressure of water vapor in pascals |
| Rd = gas constant for dry air = 287.05 J / (kg · K) |
| Rv = gas constant for water vapor 461.495 J / (kg · K) |
| T = temperature K = °C + 273.15 |
To determine the density of the air, it is necessary to know the actual air pressure,
also known as absolute pressure, or station pressure, the water vapor pressure, and the temperature.
| Calculation of the wavelength with frequency and temperature Speed of sound - temperature matters, not air pressure Calculation of the wavelength of radio waves and acoustic waves |
The speed of sound in water is approximately 1500 m/s. It is possible to measure changes
in ocean temperature by observing the resultant change in speed of sound over long distances.
The speed of sound in an ocean is approximately:
c = 1449.2 + 4.6 × T - 0.055 × T2 + 0.00029 × T3 + (1.34 - 0.01 × T) · (s - 35) + 0.0163 × z
T = temperature in degrees Celsius
s = salinity in parts per thousand
z = depth in meters
Table (chart): The impact of temperature
Speed of sound, density of air, specific acoustic impedance vs. temperature
| Temperature of air  in °C |
Speed of sound c in m/s |
Time per 1 m Δ t in ms/m |
Density of air ρ in kg/m3 |
Impedance of air Z in N·s/m3 |
| +35 | 351.96 | 2.840 | 1.1455 | 403.2 |
| +30 | 349.08 | 2.864 | 1.1644 | 406.5 |
| +25 | 346.18 | 2.888 | 1.1839 | 409.4 |
| +20 | 343.26 | 2.912 | 1.2041 | 413.3 |
| +15 | 340.31 | 2.937 | 1.2250 | 416.9 |
| +10 | 337.33 | 2.963 | 1.2466 | 420.5 |
| +5 | 334.33 | 2.990 | 1.2690 | 424.3 |
| 0 | 331.30 | 3.017 | 1.2920 | 428.0 |
| −5 | 328.24 | 3.044 | 1.3163 | 432.1 |
| −10 | 325.16 | 3.073 | 1.3413 | 436.1 |
| −15 | 322.04 | 3.103 | 1.3673 | 440.3 |
| −20 | 318.89 | 3.134 | 1.3943 | 444.6 |
| −25 | 315.72 | 3.165 | 1.4224 | 449.1 |
| Sound waves and electromagnetic waves are different. Sound waves need a medium to travel through, while the electromagnetic waves do not. The properties of a sound wave depend on the properties of the medium it travels through. |
| I am not content with this standard table Speed of Sound at Different Altitudes because it seems to tell us, that the speed of sound has to do with the altitude (height) above ground and its sound pressure. The speed of sound has really to do only with the temperature. It's cold up there. |
Converter: Fahrenheit to Celsius and Celsius to Fahrenheit
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