THE RANGE OF HUMAN HEARING

The Range Of Human Hearing



The Range Of Human Hearing

Anatomy of the Ear

A brief reminder of some components of the anatomy of the ear will help us better understand how it works.

Figure 1: Anatomy of the ear

The outer ear consists of the pinna (a) and ear canal (b). The middle ear includes the eardrum (c), the bones: the hammer (e), the anvil (f) and the stirrup (d) and the oval window (g) and the round window (h).

The middle ear communicates with the nasal cavity via the Eustachian tube (i).

The inner ear, finally, contains the cochlea (j) and the semicircular canals (l).

The auditory nerve (k) transmits sound information to the brain.

We will not discuss much of the semicircular canals here, because they are used for equilibration, and we are interested in human hearing (D'Ambrose 2003, 90).

Operation

Sound waves entering the ear drum they vibrate. These vibrations are transmitted via the ossicles to the oval window. After the oval window, the waves are transmitted to the endolymph and the membrane on which are basilar hair cells. These are sensory cells (cells there are external and internal cells corresponding to a total of about 35,000 nerve fibers) which have different sensitivity curves at the different frequencies: the cells closest to the base of the cochlea of a peak have sensitivity to the sounds the most acute, whereas cells closest to the end have a peak sensitivity to sounds more serious. The bones do not just transmit the vibrations to the inner ear; they also have a role in impedance matching. The sounds perceived by the human ear range from 20 Hz to 20 kHz.

The perception of frequency

The eye, to collect the colors (that is to say, the frequencies of waves which reach it) has cells specific to the color vision: cones. These are of three kinds (for details, see the plug on “The visual trivariance humans" who gives a quick overview of the issue). Therefore, information on the spectrum of polychromatic light will be reflected in the cones by three parameters only. This is why two different lights (that is to say various spectra) can seem to have the same color, if the impression they make on the cones is identical. We see most of polychromatic light as monochromatic light of a certain frequency, variable intensity, and more or less "white washed" (Hoelzel 2002, 101).

The laws of addition of color are the illustration of the limitations of the eye: the sum of two lights of different colors is perceived as a third color we cannot perceive frequencies up the dough, but only one frequency whose effect is equivalent to our eyes. In contrast, the ear has thousands of hair cells of different sensitivities. These cells allow many far greater frequency discrimination that the three kinds of cones of the eye.

Thus, the ear does not perceive only a "result" of all the component frequencies sound but is able to hear the spectrum of a mixture of multiple sound ...