The science behind Ondo

Acoustic thermometers rely on the principle that as air temperature varies, its density varies. The change in air density causes the speed of sound to vary according to the formula:

…where ‘t’ is the temperature in degrees Celsius.

The speed of sound can be measured by timing how long it takes for a sound to travel a known distance, ‘d’ between two points; typically, a speaker (the source of the sound) and a microphone (the receiver of the sound).  The speed can then be calculated in the usual way by dividing the distance by the time to cross the distance.

How Ondo works

Ondo generates a test sound that is played on the right ear piece speaker. This test sound is then received by the headset microphone after travelling distance (d). The transit time between the speaker and the microphone is then calculated by careful analysis of the recorded signal.

Further resources

The following links provide some additional background resources on the theory of sound:

• https://www.bbc.com/education/guides/z8d2mp3/revision/3

• https://www.texasgateway.org/resource/141-speed-sound-frequency-and-wavelength

These links provide some additional information on acoustic thermometry:

• https://www.edn.com/design/analog/4369636/An-introduction-to-acoustic-thermometry

• http://www.npl.co.uk/temperature-humidity/research/practical-acoustic-thermometry-measuring-temperature-with-sound