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Statement: Speed of sound - temperature matters, not air pressure

Calculation: Speed of sound c in air and the important temperature

Air Density Calculations

First, consider the ideal gas law:

(1)    p × V = n × R × T

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

By combining the previous two equations, the expression for the density D = ρ becomes:

(3)   

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)   

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

Impedance of Air, Density of Air, and Speed of Sound
in Dependance of the Temperature

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