Why Do Some Sounds Make People Sick?
While playing music too loudly can damage hearing, there are other things you should know about the effects of some sounds on the human body.
Decibels are used to measure the intensity of sounds (prolonged exposure to sounds above 85 dB can cause hearing loss), and frequency, which is measured in Hertz (Hz), refers to the amount of times a sound wave occurs each second. Human ears can generally pick up on sounds that fall in the 20Hz to 20KHz range. Frequencies above that are called ultrasonic, and frequencies below 20Hz are sometimes referred to as infrasonic. Infrasonic sound is both naturally occurring (earthquakes, ocean waves, upper-atmospheric lightning, etc.) and man-made. Some studies have shown that at high intensities, infrasonic sounds can have extra-aural bioeffects, including nausea, headaches, and dizziness, but why? The short answer: bad vibrations.
Sound is a wave of pressure traveling through a medium. Infrasonic sound, for example, has a long wavelength that, according to Popular Science, “makes it much more capable of bending around or penetrating your body, creating an oscillating pressure system.” Every object, including parts of the body, has a natural frequency at which it vibrates, a phenomenon known as resonance. Popular Science has more to say about how low-frequency resonance affects the body:
“Human eyeballs are fluid-filled ovoids, lungs are gas-filled membranes, and the human abdomen contains a variety of liquid-, solid-, and gas-filled pockets. All of these structures have limits to how much they can stretch when subjected to force, so if you provide enough power behind a vibration, they will stretch and shrink in time with the low-frequency vibrations of the air molecules around them.”
A 1983 study on human body vibration exposure published in The Journal of the Acoustical Society of America found that
“exposure to vertical vibrations in the 5-10 Hz range generally causes resonance in the thoracic-abdominal system, at 20-30 Hz in the head-neck-shoulder system, and at 60-90 Hz in the eyeball. When vibrations are attenuated in the body, its energy is absorbed by the tissue and organs...Vibration leads to both voluntary and involuntary contractions of muscles, and can cause local muscle fatigue, particularly when the vibration is at the resonant-frequency level. Furthermore, it may cause reflex contractions, which will reduce motor performance capabilities.”
Other studies suggest that low-frequency noises, like those produced by wind turbines, trigger a reaction in the brain that could lead to adverse health effects. The frequencies have also been linked to changes in respiratory rhythms due to chest-wall vibration, with varying results depending on whether the subject is standing or sitting (resonance occurs at different levels depending on body position). Infrasound has been used at haunted houses to make visitors feel uneasy, and some believe that there is a “brown note” (around 9Hz) that could cause bowels to release (though this was “busted” by Adam Savage and Jamie Hyneman on Mythbusters).
More research is needed to fully understand why some people are affected and others are not, but engineers have been developing sound-dampening technology for turbines, and some doctors have suggested that noise-canceling headphones may help in other cases.