This article is from the Tinnitus FAQ, by firstname.lastname@example.org (Mark Bixby) with numerous contributions by others.
Hyperacusis is defined as a collapsed tolerance to normal environmental
sounds. It is a rare hearing disorder whereby a person becomes highly
sensitive to noise. Sometimes people think they have hyperacusis because
they are bothered by loud sounds like music, heavy equipment or sirens.
This is not hyperacusis because these sounds are loud to the normal ear.
Individuals with hyperacusis have difficulty tolerating sounds which do not
seem loud to others. The ears lose much of their normal dynamic range, and
everyday noises sound unbearably or painfully loud. Simply stated, it is
like the volume control on your hearing is stuck on HIGH! Hyperacusis can
affect people of all ages and is almost always accompanied by tinnitus, an
ailment that causes sufferers to hear constant ringing, buzzing or static.
Unlike hyperacusis, tinnitus is very common and is associated with many
hearing disorders. Hyperacusis and tinnitus can affect one or both ears.
Recruitment is a similar hearing disorder which is often confused with
hyperacusis. The difference is that an individual with hyperacusis is
highly sensitive to sound but has _no hearing loss_ whereas a person with
recruitment is highly sensitive to sound but also _has hearing loss_. This
is an important difference.