Musical Acoustics

Science has taught us that sound is air molecules compressing and expanding in waves. The highest point of the waves is interpreted as amplitude and is measured in decibels. When reading these measurements, negative infinity is silence, and zero is the loudest. How many times a second the crest of the wave passes a given point is known as frequency. Frequency is measured in hertz, and musicians refer to it as pitch.

Sound can travel or propagate through three different mediums. They are liquids, solids, and gases. We perceive sound, for the most part, through the gas medium as it travels through the air at 1,126 feet per second. Depending on the medium, sound waves move faster or slower. For instance, sound travels faster through a solid than through the air because the molecules are closer together. When sound arrives at different mediums, one of the following things will happen absorption, diffusion, or reflection.

When sound is absorbed, it will stop traveling. This can be useful because it can control unwanted reverberations. If a room is “dead,” then the surfaces will absorb a large percentage of the sound. Diffusion is when the sound is broken up and reflected in many different directions. This allows the sound to be absorbed easier and, at the same time, prevents standing waves which we will discuss later in this section. When the sound bounces off the surface of the medium, it is called a reflection. This is heard in reverberations and, for the most part, is beneficial but can lead to problems such as standing waves.

Standing waves are most commonly found in rooms with parallel walls allowing sound waves to cancel each other out. When one sound wave is reflected in the exact opposite of itself or 180 degrees out of phase, it will cancel itself out. When this occurs, the sound wave loses energy and therefore becomes quiet. Another major problem that can occur is low-frequency build-up. Low frequencies are harder to absorb and, therefore, can become out of control easier. As the low frequencies build-up phase, issues become apparent. This can cause the listener to perceive the bass as missing. In addition, the human ear has a hard time perceiving low frequencies. These issues can lead the listener to overcompensate with their recording techniques.

Wherever you are recording, whether at home or in the studio, try to keep the concepts we discussed in mind. If you are having issues, some useful tips might be to try and angle your sound source so that it is not pointed directly at any walls. This will help to avoid phase issues. In addition, try not to record in any room that is completely square. Curtains, blankets, and other sound dampeners can help to absorb sound but remember that they will only stop mid to high frequencies and cannot help with any low-frequency build-up issues. Be sure to experiment with rooms, as you never know what amazing sounds you might find in some hidden room at your location.