Noise and sound: Overview
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About sound
Sound is energy that's produced through vibrations that travel through air, water and solid materials in the form of waves.
Sound can be separated into 3 categories:
- audible sound
- infrasound
- ultrasound
Audible sound is the range of medium frequency sound waves that most humans can hear. In general, a young person with normal hearing can hear sounds with frequencies between 20 Hz and 20,000 Hz. People lose the ability to hear higher frequencies in this range as they age.
Infrasound is the range of low frequency sound waves below 20 Hz and outside the range that humans can typically hear. Natural events such as earthquakes and volcanos can cause infrasound. Scientists can measure changes in levels of infrasound to help detect earthquakes or forecast volcano eruptions.
Ultrasound is the range of high frequency sound waves that humans typically don't hear. Medical professionals use ultrasound to create an image of tissues inside of the body.
How sound is measured
Scientists use A-weighted decibels (dBA) to describe how loud a sound is to humans. The hearing threshold for an average adult is 0 dBA. The sound of breathing is around 10 dBA and is barely perceptible. A normal conversation would measure at around 60 dBA.
Depending on how loud a noise or sound is and how long you are exposed, it can cause:
- hearing loss, tinnitus or both
- negative effects on mental health and well being