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  • Lance Csarmasz Kuyper

Principle of Sound - Part 2



In part one of my “Principles of Sound” blog, I covered the importance of understanding sound. I also detailed why sound is so important to an audio engineer. However, sounds are very complex. A great deal more goes into sound than we might realize. For instance, it helps to understand the speed sound travels at 1,130 feet per second. This concept can be affected by things such as elevation, temperature, and humidity. It also serves to understand how we identify and measure sound. Sound is measured in cycles per second (CPS) or hertz (Hz). Hertz and Cycles-per-second are synonymous terms for application. One sound wave is considered a cycle and is measured on a 360-degree graph starting at zero degrees. The soundwave pushes against our eardrum creating compression, which takes us to the 180-degree line. See graph! Then as the air molecules return to their original resting position, the eardrum is pulled out (also called rarefaction), which takes us the remainder of the way on the graph to 360 degrees. This compression and rarefaction of a sound wave create one complete sound wave cycle.



The number of cycles in a second determines the frequency or pitch of the sound wave. A sound wave with very few cycles will create a lower pitch. A sound wave with a larger number of cycles will make a higher pitch. It is also important to remember that lower frequencies have much longer sound wave cycles than higher frequencies. A single waveform is called a sine wave. However, most sounds are usually much more complex and made using multiple sine waves combined.

Another component of a sound wave is the height of the sound wave. Sound wave height is measured in amplitude. For audio engineers, the amplitude is measured in gain or decibels (dB). Although amplitude does relate to our perception of loudness, the relationship is not 1:1. The Human ear will perceive some frequencies as louder than others as defined scientifically with the Fletcher Munson Curve or the Equal Loudness Principal. Though it really should be called the unequal loudness principle. Essentially this means that it takes more amplitude to hear low and high frequencies than it does to hear mid-range frequencies.