A review of how the human ear works:

The human ear is an amazing mechanism, but not as efficient as those belonging to some of our friends in the animal kingdom. Some foxes, for example, have the ability to direct their outer ear to detect even ants moving underground. That would be dandy if ants happen to be a source of survival, but most humans would settle for hearing the news on TV, or a grandchild’s laughter.
To refresh what most of us learned in junior high school health class, the ear has three basic components: the outer ear, middle ear and inner ear. The outer ear consists of the skin and cartilage that hangs on both sides of your head and the ear canal, which extends about an inch inside the head. This canal not only protects the delicate inner parts of the ear, but actually amplifies the resonance of certain pitches necessary for understanding speech.
The middle ear consists of the eardrum, the ossicles (tiny bones nicknamed the hammer, anvil and stirrup), and the Eustachian tube. The eardrum is highly sensitive to vibration which it passes along to the ossicles; they, in turn, compress it; focusing all the vibration onto the tiny footplate of the stirrup. Because sound is nothing more than a vibration in the air, the body’s internal amplifier needs air provided by the Eustachian tube. It has one open end in the middle ear and the other end in the back of the throat, and provides a way to equalize pressure.
The inner ear consists of the snail-like cochlea, the semicircular canals and the endings of the auditory nerve. The intensive vibration of the stirrup on the oval window that connects the middle and inner ear creates a wave in the fluid filling of the cochlea, setting in motion its tiny hairlike projections, which then contact the nerve endings. The nerve carries the signal to the brain for interpretation.
With all this delicate machinery, it is easy to see how something might go wrong along the way. Sometimes it is as simple as an accumulation of wax in the ear canal, which may only get packed deeper when you try to clean it out. In other cases, a perforated eardrum can result from an injury or an illness and cause temporary hearing loss. The fragile inner ear is subject to infection by a variety of viruses including mumps and measles and any illness accompanied by a very high fever.
In a conductive hearing loss, the outer or middle ear does not conduct sound as well as it should, primarily causing a loss of sensitivity for hearing soft sounds. When the problem is in the inner ear, stemming from disease, injury or age (where the transmitter is operating but the brain isn’t picking up the signal), this is misleadingly referred to as “nerve deafness.” With this sensorineural hearing loss, there is a reduced sensitivity to soft sounds as well as difficulty in clearly distinguishing one sound from another.