Unlike light waves, sound waves do not travel in a vacuum, as in outer space. Sound waves are the result of the vibration of particles of air. Vibrations of the air created by your voice, musical instruments or audio speakers travel through the air at the speed of sound, also called Mach 1. The speed of sound depends on several factors, but through the air, at sea level, and with the air temperature at 59 degrees Fahrenheit (15 degrees Celsius) — the speed is 761.2 mph (1,225 km/h). Because gas molecules move more slowly at colder temperatures, that slows the speed of sound; sound moves faster through warmer air.

Let’s not confuse the speed of sound however with the loudness or the pitch of the sound. The louder the sound, the greater the disturbance of the air particles. This is called amplitude. The higher the sound (like a flute), the more rapid are the cycles of the compression waves. This frequency of the compression waves through the air is called the pitch. It is an expression of the rates of compression and rarefaction of the air particles.

The human ear can detect frequencies of approximately 20 cycles per second up to approximately 20,000 cycles per second. Cycles per second is expressed as Hertz or Hz. Another way of expressing 20,000 cycles per second would be to say 20 kHz. (or twenty kilohertz). It is possible to modulate the air particles slower than 20 Hz and faster than 20 kHz, and there are disturbance waves in the air traveling faster and slower than we can hear. They are called subsonic and supersonic.

For a refresher on metrics see here.

For a further brief visual explanation of sound waves, see here.

For the next post in understanding vision and how we develop an internal model of the world around us, see here.