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This calculator is to determine the speed of sound inhumid 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 to 303.15 K) and over the pressure range 75 to 102 kPa. In the region between the air pressures 95 and 104 kPa there is no noticeable changing of the speed of sound c. The standard air pressure 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 really good
to air, in good approximation and can be regarded as an ideal gas. Environmental effects change the speed of sound and the absorption of sound in air. Even seemingly small percentage changes may cause serious listening problems in enclosed acoustic spaces. The air pressure is entered here anyway, it could be that you have to involve a pressure far from normal. Don't forget, this is a site for sound designers. |
| Notice for musicians and technicians (not for physics professors): 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 in the case of "speed of sound". The temperature indication, however, is absolutely necessary. Changing of the air pressure does not change the sound of musical instruments in concert halls or in a rooms. |
| Google is not correct (look at the following link) http://www.google.com/search?q=speed+of+sound+at+sea+level 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 important temperature, and the given atmospheric pressure "at sea level" makes really no sense. |
In SI units with dry air at 20°C (68°F), the speed of sound c is 343 meters per second (m/s). |
 |
| That means, the ratio p_ / ρ is always constant on a high mountain, and even at "sea level". The static atmospheric pressure p_ and the density of air ρ go always together. The ratio stays constant. When calculating the speed of sound forget the atmospheric pressure, but look accurately at the very important temperature. The speed of sound varies with altitude (height) only because of the changing temperature! |
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.
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. The speed higher than Mach 1 is called supersonic speed. |
| 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 around that is transonic. Mach number above 1 means the flow velocity is higher than the speed of sound - and the speed is supersonic. More than Mach number 5 is called hypersonic. |
| M < 1: Subsonic flow M = 1: Sonic flow M > 1: Supersonic flow |
| Mach number | M < 0.3 | 0.3 < M < 1 | M = 1 | M ≈ 1 | 1 < M < 5 | 5 < M |
| Name | Low subsonic | High subsonic | Sonic | Transonic | Supersonic | Hypersonic |
| Frequency dependent attenuation of air (dB) in 30 m distance at different humidity (percent) |
 |
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 = specific 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 =specific gas constant = 287.058 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 / (287.058 × (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 = specific 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.
| In 1970, the pressure reference level of 0 dB ≡ 1 µPa was chosen by the US Navy for their underwater work for sound in water. For an identical source intensity in water and air, the sound pressure generated in water will be about 60 times greater than in air. |
| 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 |
Notice: Air pressure p and air density ρ are not the same.
In gases, the higher the velocity of sound, the higher the pitch will be, when you sing.
Only because of the decreasing air temperature, which decreases with altitude, the speed of sound decreases.
| 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. |
Change of speed of sound with the change in height
| The standard table: Speed of Sound at Different Altitudes The speed of sound is not a constant, but depends actually on the temperature at that altitude. The speed of sound changes only with temperature. Sure, it's just very cold up there. |
Change of air pressure associated with the change in height
| Question: How does the air pressure change if the height changes 1 meter? The hydrostatic pressure is calculated according to Blaise Pascal:  This law is also assumed as an air column. Height h = 1 m Standard gravitational acceleration is g = 9.80665 m/s2 Density of air at 20°C is ρ20 = 1.204 kg/m3 1 m height changes the air pressure at a constant temperature of 20°C by p = ρ20 ∙ g ∙ h = 1.204 kg/m3 × 9.80665 m/s2 × 1 m = 11.8 Pa (N/m²) Rule of thumb: At ground level the air pressure decreases by 1 hPa = 100 Pa with an altitude change of 8.5 meters. But the temperature has a tendency to decrease with height. |
Converter: Fahrenheit to Celsius and Celsius to Fahrenheit
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