Spring is in the air. Among all the beautiful blooming trees and flowers come the sounds of the season. Birds chirping, babbling brooks, and the somewhat less pleasant shrill shriek of babies crying. Humans can hear a moderately broad frequency spectrum of 20 Hz to 20,000 Hz; from the low rumble of a diesel engine idling to the thin hiss of carbonation exiting your favorite beverage upon opening.
Studies have shown that what humans typically perceive as pleasant or unpleasant sounds is fairly universal. Some of the most pleasant sounds are applause, water flowing, and thunder, while some of the most unpleasant are a fork scraping glass, an electric drill, chalk on a blackboard, or a baby crying. The overall volume of the source sound does factor into what humans find unpleasant or painful, but annoying sounds also tend to have something else in common – their frequency range. This is due to our ear canal resonance.
Resonance occurs when a source sound or vibration is equal to the natural frequency of a receiving object causing the receiving object to vibrate in unison and as a result, amplify the source. The length, volume, and curvature of our ear canals result in a natural frequency range of 2000 Hz – 4000 Hz, causing sounds in that spectrum to be amplified.
The amygdala is the part of the brain that regulates emotion. When someone hears an extremely unpleasant sound, there is a heightened emotional response in the brain. The intense emotional response is tagged as important prior to our brains having a chance to fully process the unpleasant sound. This subconscious reaction is part of what helps to keep us alive, and is related to our fight-or-flight response.
Whether you are a parent or not, your body subconsciously switches into alert mode when you hear the frequency content of a baby’s cry. This makes you more aware and present, ready to react to the situation at hand. It is possible that this is a part of human evolution, the tuning of our ear canals to recognize sounds that require our attention or immediate response. Next time you are irritated by the sound of a baby crying on a plane, remember that this is the same response experienced by parents throughout their child’s infancy- a sound that is guaranteed to wake you from a deep sleep or that you will hear above all other distractions. Instead of dismissing the infant’s cries as a nuisance, consider this as an example of our primitive survival skills.