Sound is perceived through the sense of hearing. Humans and many animals use their ears to hear sound, but loud sounds and low frequency sounds can be supposed by other parts of the body through the sense of touch. Sounds are used in several ways, most notably for announcement through speech or, for example, music. Sound can also be used to acquire information about properties of the neighboring environment such as spatial characteristics and presence of other animals or objects. For example, bats use echolocation, ships and submarines use sonar, and humans can determine spatial information by the way in which they perceive sounds.
The range of frequencies that humans can hear well is between about 20 Hz and 16,000 Hz. This is by description the hearing range, but most people can hear above 16,000 Hz provided the sound pressure level is above the hearing threshold level. At 40,000 Hz and higher frequencies, for instance, this level is about 140 dB. The audible range varies by individual and, mostly in the upper part of the range, hearing damage accumulates with age. The ear is most sensitive to frequencies around 3,500 Hz. Sound above the hearing range is known as ultrasound and that below the hearing range as infrasound.
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