why children below the age of 5 could here 25 kilohertz frequency sound above the range of normal human hearing ?
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In humans, sound waves funnel into the ear via the external ear canal and reach the eardrum (tympanic membrane). The compression and rarefaction of these waves set this thin membrane in motion, causing sympathetic vibration through the middle ear bones (the ossicles: malleus, incus and stapes), the basilar fluid in the cochlea, and the hairs within it, called stereocilia. These hairs line the cochlea from base to apex, and the part stimulated and the intensity of stimulation gives an indication of the nature of the sound. Information gathered from the hair cells is sent via the auditory nerve for processing in the brain.
The commonly stated range of human hearing is 20 Hz to 20 kHz.[4][5][note 1] Under ideal laboratory conditions, humans can hear sound as low as 12 Hz[6] and as high as 28 kHz, though the threshold increases sharply at 15 kHz in adults, corresponding to the last auditory channel of the cochlea.[7] Humans are most sensitive to (i.e. able to discern at lowest intensity) frequencies between 2,000 and 5,000 Hz.[8] Individual hearing range varies according to the general condition of a human's ears and nervous system. The range shrinks during life,[9] usually beginning at around age of eight with the upper frequency limit being reduced. Women typically experience a lesser degree of hearing loss than men, with a later onset. Men have approximately 5 to 10 dB greater loss in the upper frequencies by age 40.
The commonly stated range of human hearing is 20 Hz to 20 kHz.[4][5][note 1] Under ideal laboratory conditions, humans can hear sound as low as 12 Hz[6] and as high as 28 kHz, though the threshold increases sharply at 15 kHz in adults, corresponding to the last auditory channel of the cochlea.[7] Humans are most sensitive to (i.e. able to discern at lowest intensity) frequencies between 2,000 and 5,000 Hz.[8] Individual hearing range varies according to the general condition of a human's ears and nervous system. The range shrinks during life,[9] usually beginning at around age of eight with the upper frequency limit being reduced. Women typically experience a lesser degree of hearing loss than men, with a later onset. Men have approximately 5 to 10 dB greater loss in the upper frequencies by age 40.
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