Sound is all around us and so much a part of most people’s daily lives that we often don’t even realize all the different sounds in our environment. In fact, we are so used to sounds that it can come as a bit of a shock to be in complete silence.

Sound is a form of energy transfer and results whenever an object vibrates. These vibrations are transferred to the particles of a medium like the air which vibrate back and forth creating areas of high pressure (compressions) and low pressure (rarefactions). This creates a longitudinal wave that travels to your ears, where you experience it as sound that you hear.

The distance between each successive compression or peak is called the wavelength. The shorter the wavelength, the more complete waves pass a given point each second. We measure how many waves pass per second as the frequency. One hertz (1 Hz) is one full wave per second.

Sound waves with a high frequency are heard as high pitched. Sounds with a low frequency are heard as low pitched. Humans can hear sounds with a frequency of between 20 Hz and 20 000 Hz.

But sound is not just useful for perceiving, interacting with, and making sense of the world. Engineers have found truly ingenious ways to put sound to some other uses, as we will see.