What is Sound?

Before touching on equipment or technique, it is important to understand exactly what sound is and how it works.  While there are far more scientific aspects involved with the subject of sound than what I am going to cover here, my goal is to break things down in a way that musicians will relate to.

A great definition of sound comes from mediacollege.com, which says:  “Sound waves exist as variations of pressure in a medium such as air. They are created by the vibration of an object, which causes the air surrounding it to vibrate.  The vibrating air then causes the human eardrum to vibrate, which the brain interprets as sound.”

Sound waves are created much in the same way as waves in water.  If you place your finger in a tub of water and move it back and forth, you immediately begin to see ripples forming and moving outward from the point of contact.  These ripples exist because:  a)  you, as the source, caused a vibration;  and b)  the vibration you caused had a medium to travel through — the water.  With sound, you have many possible sources — e.g. a hammer striking a piano string, someone’s voice resounding, a mallet striking a drum — which produce vibrations that travel through the air and finally to your eardrum.  Your eardrum is an incredibly sensitive membrane that will vibrate at even the slightest pressure created by sound waves.  The waves then travel through the inner ear, which is lined in rows with tiny hairs that act as receptors.  The vibrations pass along these hairs, reacting to the frequencies of the waves that pass through, and produce the sensation of hearing.  Hearing loss can occur when these tiny hairs are bombarded with too much pressure all at once, or too frequently, thus causing the hairs to essentially lie down flat and no longer be able to experience the sensation of sound waves traveling through.

Each sound wave has its own unique set of characteristics that are primarily defined by three things:  1.  Wavelength  2.  Frequency  3.  Amplitude

Wavelength — Measurement from the crest of one wave to the crest of the next.  High-pitch sounds have short wavelengths, while low-pitch sounds have long wavelengths.

Frequency – The number of sound wave cycles completed per second.  A cycle is one complete peak and fall of a sound wave or one vibration of the vibrating source.  Frequency is measured in Hertz (Hz).  The average human ear picks up on frequencies (or pitches) that range from 20-20,000 Hz.  The low sound of a tuba vibrates around 25 Hz, whereas the frequency of a C piccolo lands right around 587 Hz.

Amplitude – Essentially the height of the wave from its equilibrium point.  Amplitude refers to the intensity or loudness of the wave and is measured in decibels (dB).  The average conversation is spoken at about 70 dB, whereas levels around 130 dB would be akin to standing next to the engine of a jet.  The sound pressure of 130 dB is such that it will cause pain and potential damage to your ear drum.

If you would like to delve more into the subject of sound waves and their characteristics, then www.mediacollege.com offers supplemental information as well as audio examples of some of the things we have covered here.  There’s also a great (and inexpensive) book by Jerry Slone called The Basics of Live Sound that offers a great crash-course without all of the engineer “jargon.”

Now that you have an understanding of what sound is and how it works, we will next discuss what the job of a sound engineer entails.  Stay tuned!