Acoustic energy is a property of a periodic pressure wave, or a single pulse, propagating through an elastic medium.
 Biological sound
Human beings can usually perceive acoustic energy between the frequenies of 20–20,000 Hz, which is the basis of hearing. Human beings hearing depends on age of the listener : children hear better than adults or old people. Men tend to hear a lower range than women (it would be useful to give reference about it).
 High frequencies
Many animals can hear much higher frequencies than humans. A dog whistle produces sounds up to approximately 22 KHz; humans generally cannot hear the frequencies above 20 KHz, and often substantially below that. A cat can hear frequencies at least as high as can a dog, but simply may not be interested in them.
Bats use even higher frequencies to navigate and avoid collisions. Depending on the species, a bat may be able to use frequencies as high as 100 KHz. 
 Low frequencies
Some animals, such as whales and other cetaceans, communicate, or possibly navigate, with infrasound below the lower limit of human hearing.  Blue whales, for example, often produce fundamental frequencies in the 10-40 Hz range. High-power acoustic energy generated by humans may have effects on cetaceans.
 Applications of acoustic energy
Within the human hearing range, of course, acoustic energy is the mechanism by which speech and music are produced. There are a wide range of medical applications in which acoustic energy above the human hearing range may be used.
Sonar relies on the transmission and reflection of acoustic energy through water. Sonar signals tend to be in the higher frequencies, including ultrasound, but long-range sonar may use low frequency or infrasound.
- ↑ Cancel, Juan (1998), "Frequency of Bat Sonar", in Elert, Glenn, The Physics Factbook™, http://hypertextbook.com/facts/1998/JuanCancel.shtml
- ↑ List of whale songs, http://www.smso.net/List_of_whale_songs
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