The vibrations of air that we perceive as sound are everywhere--streaming out of mouths, traffic, roadwork, music, movies, video games and more.
Measuring What We Hear
The energy of sounds is measured in decibels (dB). With every increase of 10dB, the loudness of sounds doubles.
Sound frequencies are measured in Hertz (Hz). The spectrum of sounds used in speech is a curved shape called the "speech banana" (see below).
Person A: This person can hear every sound beneath the two blue lines, representing the left and right ears. Understanding speech is easy because she hears all the vowels and consonants.
Person B: This person can hear only the sounds below the red lines, again representing the left and right ears. Because she misses many consonants, speech sounds are muffled and difficult to understand.
Sources: Hearing Alliance of America, National Institute for Occupational Safety and Health, American Speech-Language-Hearing Assn.