| Deutsche Version |  |
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| 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 |
| −25 | 315.72 | 3.165 | 1.4224 | 449.1 |
| −20 | 318.89 | 3.134 | 1.3943 | 444.6 |
| −15 | 322.04 | 3.103 | 1.3673 | 440.3 |
| −10 | 325.16 | 3.073 | 1.3413 | 436.1 |
| −5 | 328.24 | 3.044 | 1.3163 | 432.1 |
| 0 | 331.30 | 3.017 | 1.2920 | 428.0 |
| +5 | 334.33 | 2.990 | 1.2690 | 424.3 |
| +10 | 337.33 | 2.963 | 1.2466 | 420.5 |
| +15 | 340.31 | 2.937 | 1.2250 | 416.9 |
| +20 | 343.26 | 2.912 | 1.2041 | 413.3 |
| +25 | 346.18 | 2.888 | 1.1839 | 409.4 |
| +30 | 349.08 | 2.864 | 1.1644 | 406.5 |
| +35 | 351.96 | 2.840 | 1.1455 | 403.2 |
= Temperature, c = Speed of sound, ρ = Density of air, Z = Acoustic Impedance of air
| 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. |
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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. |
The effect of temperature
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The air density ρ is: ρ = p / R · T in kg/m3 Air pressure= p, Gas constant = R, Temperature in Kelvin = T The individual gas constant R for dry air is: R = 287,058 J / kg · K with energie Joule (J) = Newton · Meter = N m; T in Kelvin = Temperature in °C + 273,15. Atmospheric pressure p0 = 101325 Pa = 1013,25 mbar = 1013,25 hPa und R = 287,058 J/kg · K. With T0 = 273,15 K (0 °C) (Normalbedingungen) ist die Luftdichte: ρ0 = 101325 / (287,058 · 273,15) = 1,2922 kg/m3. For T25 = 298,15 K (25 °C) (Normal conditions) the density of air is: ρ25 = 101325 / (287,058 · 298,15) = 1,184 kg/m3. Furthermore it is customary T20 = 293,15 K ⇔ 20 °C and the density of air is ρ = 1,204 kg/m3. As you see, this sizes are strongly temperature dependent. The speed of sound in air is: 
is the temperature in degrees Celsius.Z0 = ρ0 · c |
| 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. Generally we take with sufficient accuracy the formula (equation) for the speed of sound in air in m/s vs. temperature (theta) in degrees Celsius (centigrade):
That gives e.g. at = 20 °C a speed of sound c = 331 + 0.6 × 20 = 343 m/s.
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| Calculation of the Speed of Sound in Air and the important Temperature Speed of sound - temperature matters, not air pressure Calculation: speed of sound in humid air |
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