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It is approximately the quietest sound a young human with undamaged hearing can detect at 1 kHz. [4] The threshold of hearing is frequency-dependent and it has been shown that the ear's sensitivity is best at frequencies between 2 kHz and 5 kHz, [5] where the threshold reaches as low as −9 dB SPL. [6] [7] [8]
The ear's shape also allows the sound to be heard more accurately. Many breeds often have upright and curved ears, which direct and amplify sounds. As dogs hear higher frequency sounds than humans, they have a different acoustic perception of the world. [24] Sounds that seem loud to humans often emit high-frequency tones that can scare away dogs.
The human auditory system is sensitive to frequencies from about 20 Hz to a maximum of around 20,000 Hz, although the upper hearing limit decreases with age. Within this range, the human ear is most sensitive between 2 and 5 kHz, largely due to the resonance of the ear canal and the transfer function of the ossicles of the middle ear.
Normal human ears can discriminate between two frequencies that differ by as little as 0.2%. [14] If one ear has normal thresholds while the other has sensorineural hearing loss (SNHL), diplacusis may be present, as much as 15–20% (for example 200 Hz one ear => 240 Hz in the other).
Depending on the presence of hearing protection devices, whether the sound came unexpectedly, and where the sound originated—whether in free field, at the ear canal entrance, or at the eardrum position—the AHAAH model could predict the displacements in the inner ear because it was conformal with the structure of the human ear. [15]
The eardrum is an airtight membrane, and when sound waves arrive there, they cause it to vibrate following the waveform of the sound. Cerumen (ear wax) is produced by ceruminous and sebaceous glands in the skin of the human ear canal, protecting the ear canal and tympanic membrane from physical damage and microbial invasion. [5]
Earmuff HPDs typically consist of two ear cups and a head band. [56] Earplug style hearing protection devices are designed to fit in the ear canal. Earplugs come in a variety of different subtypes. [56] Some HPDs reduce the sound reaching the eardrum through a combination of electronic and structural components. Electronic HPDs are available in ...
Human hearing extends in frequency from 20 to 20,000 Hz, and in intensity from 0 dB to 120 dB HL or more. 0 dB does not represent absence of sound, but rather the softest sound an average unimpaired human ear can hear; some people can hear down to −5 or even −10 dB.