# Sound Location with the Qwiic Sound Trigger and the u-blox ZED-F9x

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Contributors: PaulZC

## The Speed Of Sound

We all know that sound travels slower than light. If you see a flash of lightning, it can be several seconds before you hear the clap of thunder. It’s roughly 5 seconds for every mile. Count 15 seconds and the storm is 3 miles away from you. But let’s go metric.

The speed of sound is about 343.42 metres per second (767 mph). But it changes with both temperature and humidity. It is 343.42 m/s at 20 °C (68 °F) at 0% humidity. On a hot, cold or wet day, it changes. It changes with pressure / altitude too because the temperature of air is linked to its pressure through the Ideal Gas Law. You might remember that from your chemistry lessons at school.

The equation we are going to use for the speed of sound is:

Speed of Sound (m/s) = 331.3 + 0.606T

where T is the temperature in Celcius (Centigrade), not Kelvin.

So, the speed changes by approx. 0.6 metres per second or 0.2% for every degree change in temperature. We’ll include that in our calculations.