Chapter One: An Acoustics Primer

### 3. How fast does sound travel?

The speed at which sound** propagates** (or travels from its source) is directly influenced by both the medium through which it travels and the factors affecting the medium, such as altitude, humidity and temperature for gases like air. Bad news for Star Wars fans—there is no sound in the vacuum of space because there are too few molecules to propagate a wave.

It is important to note that the speed of sound in air is determined by the conditions of the air itself (e.g. humidity, temperature, altitude). It is not dependent upon the sound’s amplitude, frequency or wavelength. To calculate the *approximate* speed of sound in dry air at sea level, use the following formula:

**V ≈ 331.4 + 0.6T _{c}
**V = velocity (m/s), T

^{c}= temperature in Celsius

Using this formula, the *approximate* speed of sound at 20° Celsius (68° Fahrenheit) is:

344 meters per second (m/s) |

1128 feet per second (f/s) |

770 miles per hour (mph) |

Use the calculator below to compute the approximate speed of sound at other temperatures.

**Mini-factoid:** The linear equation above works well to approximate the SOS inside a limited temperature range and some of you may have noticed that the given standard speed values for 20º C above are* not exactly *what you would get using that equation. A more accurate formula (V = velocity in m/s, T^{c} = temperature in Celsius):

This formula indicates that the speed of sound (in air) is proportional to the square root of temperature.

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