“I’ll begin with a disclaimer — sound is incredibly complicated. First, it involves a serious understanding of physics, biology, mathematics and material science. Then we will add the fact that hearing is subjective, and a person’s perception of it differs from one to the next, and the ear is a nonlinear system.”

Alanna Watts, PE, presented “The Basics of Sound and Noise – And the Perception of Sound” at PSCU 2018. The presentation included an understanding of sound by beginning with its history. Greeks used materials they could see to study sound – the pluck of a string and the ripples of a pebble being dropped into water. Pythagoras and Aristotle were among the first philosophers who made hypotheses about sound, many of which align with what is known about sound today.

Alanna’s presentation was motivated by her personal history with hearing loss due to a genetic condition involving bone growth in her middle ear that exacerbated her hearing loss at age 21. The overgrowth was corrected with surgery, and now she brings a unique perspective and passion to engineering projects including a school for the deaf and nursing homes.

Sound is not merely the disturbance in the air or other elastic media; it is also a sensation. Noise is often described as an annoyance and is subjective from person-to-person. Alanna’s examples of noise included white noise such as an air conditioner or radio static. Pitch and harmony play roles in what people find pleasing in sound or describing something as a noise.

In engineering, there are several factors that can affect how sound is heard in a space. Alanna talked about frequency and wavelength in comparison and how refraction, reflection, spaciousness, diffusion, diffraction, reverberation, modal resonance, and absorption can change a sound.

“In most rooms, in addition to direct sound, reflections from the enclosing surfaces affect the way the sound level decreases,” she said. “In contrast to free fields, in a perfectly reverberant solid field, the sound level is equal everywhere. Most rooms are a combination of these two extremes.”

Different materials and layouts of a space can help to amplify or dampen sounds. Again, she said that a lot of what people are able or not able to hear is subjective.