Sound Waves: "In the Beginning..."

Dim the lights and grab a bowl of popcorn for this classic film on Sound Waves. This is a great explanation of where sound comes from. I took the liberty of typing up a short article to go along with the video. 


Where does sound come from?

Sound waves are audible vibrations in the air. Just like a rock thrown into water will produce a ripple, when you strike an object that’s in contact with air it will produce sound. The pushing up of the wave is called compression and downward pull is rarefaction. 

    One complete complete compression and rarefaction defines a cycle. The length of time it takes to complete a cycle is the wavelength. This unit of time is measure in Hertz, Hz. The shorter wavelength is faster and higher in pitch. The longer wavelengths take longer and are lower in pitch.

[For example, 5,000Hz sounds much higher than 50Hz. This is like comparing a bee buzzing passed your ear to a semi-truck passing by you while you’re walking down the street. The bee is producing higher frequencies, whereas the semi-truck is producing lower frequencies; your soiled pants in both situations is just a coincidence.]

Characteristics of Sound

Cycle - one complete push and pull of air

Wavelength - the length of a cycle

Hertz (Hz) - time it take to complete a cycle

Frequency - number of cycles completed in 1 sec *measured in Hertz (Hz)

Phase - Constructive or Deconstructive “combination” of wave forms.

Amplitude - Loudness *measured in decibels

Timbre - variations in a sound wave that make it sound unique.

Science of Sound

So why is the science of sound waves important for a sound guy to know, will it ever get used? The answer is yes. Microphones, mixers, speakers ( just to name a few tools ) are all used to capture, manipulate, and reproduce sound. So understanding the basic science they are built on will benefit your ability to use them well.
 
If this topic interest you, check out this book; Modern Recording Techniques. It's been the standard introduction to understanding sound and recording for years.