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Tyler Stowe
Acoustics is branch of physics concerned with the properties of sound. It also refers to the properties and qualities of a room or building that determine how sound is transmitted in it. The history of acoustics goes back thousands of years. We have unconsciously been utilizing its properties since ancient times. Many famous and brilliant men over hundreds of years, contibuted theories and discoveries that help shape the audio world today.
In the 6th century B.C. Greece, Pythagoras was experimenting with muscial intervals. He noticed that when lengths of vibrating strings are ratios of certain integers, the tones would be harmonious. He found that an A note struck on a string would be the same on a string twice as long but an octave lower.
In the 4th century B.C. Greece, Aristotle wrote that an impact or a sharp blow in the air was needed to create sound. He wrote his theory in his de Anima. He was the first to give thought to reverberation.
2,200 years later, Marin Mersenne wrote the L’harmonie Universelle which describes the frequency of oscillation of a stretched string.
In 1638, Galileo postulated that vibrations of a body produced waves that travel through the air into our ears.
Leonardo da Vinci proposed that sound moves in waves. He wrote the Codex Atlanticus where he conceptualized the viola organist, the first bowed keyboard instrument.
In 1635, Pierre Gassendi was the first person to measure the speed of sound. His calculation was very accurate to the figure we use today.
In 1660, Robert Boyle determined that in order for sound to propagate, the medium it’s in must be air or liquid.
Isaac Newton concocted an experiment that showed the correlation between the speed of sound in various gases. He did this by relating the density and compressibility in a controlled medium.
In the 17th century, Athanasius Kircher did an experiment were instead of putting a trumpet to his mouth, he put it to his ear. He instantly noticed that the trumpet amplified sounds making them seem louder than normal.
Many experimental scientist tried to determine the human hearing range. They came up with many different figures. In the 1840s, scientists Toepler, Boltzman, and Rayleigh found that the minimum audible amplitude for humans was a sound pressure of 20 micropascals
Sound has many charcteristics. To audio engineer, knowing these characteristics and behavior allows them to create better recordings and music. Acoustic absorption is the absorption of sound energy when a sound wave strikes a surface in an environment. The way sound is absorbed depends on the frequency of the sound, the angle at which the sound wave hits a surface, and any impedances in the air or the surface it hits. Acoustic attenuation is the measure of the energy loss of sound propagating in some media. Acoustic impedance(Z) is the opposition to the flow of sound through some media. Diffraction is the bending of waves around small obstacles and the propagation and spreading through openings and around corners. Diffusion describes the tendency for sounds to spread out evenly in a consistent medium. Refraction is the bending of sound when entering a medium where its speed is different. It is dependent on angle of which it enters or strikes new medium. Scattering is the irregular reflection, refraction, and diffraction of sound waves in many directions.
When creating a studio there are many things you can do to produce the results you want. In almost every studio you will find absorbers, acoustic foam, bass traps, diffusers, and monitors. Absorbers are any material or structure that is particularly acoustically unreflective. Soft, rough, and porous materials make the best absorbers. Larger soundwaves require a larger absorbing device. These absorbers can be placed at key points of first reflection around the mix position, very generally to the left, right, above, and behind the mix position. Acoustic foam is an open celled, lightweight, uncompressed material selected/designed for its ability to absorb sound. It is made from polyurethane foam or extruded melamine foam. It is usually comes cut into tiles, often with pyramid or wedge shapes in varying different colors, sizes, and thicknesses. This foam reduces noise levels, reflections, and vibrations, and resonance. it deals with mid and high frequencies. For increased effectiveness, leave an air gap between panels and wall. Bass traps are acoustic absorbers that are designed to absorb low frequency sounds. They are usually placed in corners and are the largest of absorbers available. They allow the bass to bounce around the enclosure instead of back into the room. Bass traps come in two types, resonating and porous. Resonating bass traps tend to work on a narrow band of frequencies and porous bass traps tend to absorb a broader band of frequencies. Porous traps are smaller and easier, and don’t need to be calibrated. Diffusers are structures designed to scatter or disperse acoustic energy throughout a given space. They redirect and redistribute sound waves throughout the room, helping to eliminate hot spots and dead spots while preserving some room sound.
