Phonophobia is a fear of loud sounds, especially sudden and unexpected ones.
For example, listening to a CD that starts with a minute of silence and then suddenly goes into loud rock music would be extremely startling for most people, assuming they had no prior knowledge of the content of the CD. Being startled is in itself a normal reaction, but the key difference is that people with Phonophobia actively fear such an occurrence.
Phonophobics may be fearful of devices that can suddenly emit loud sounds, such as computer speakers or fire alarms. When operating a home theater system, computer, television, CD player, etc., they may wish to have the volume turned down all the way before doing anything that would cause the speakers to emit sound, so that once the command to produce sound is given, the user can raise the volume of the speakers to a comfortable listening level. However, the most common situation where Phonophobics experience their fear is exposure to explosive sounds, such as those produced by fireworks, firecrackers and other pyrotechnic devices. This usually prevents Phonophobics from attending events or festivals where they think these devices can be used.
Another example is watching someone blow up a balloon beyond its normal capacity. This is often an unsettling, even disturbing thing for a person with Phonophobia to observe, as he or she anticipates a loud sound when the balloon pops. Other sounds include a car backfiring, a sudden train whistle (especially electric trains) and loud parts of a movie.
Phonophobia is often found in people with autism, particularly children (though it also affects a large number of non-mentally handicapped individuals). Such people may be afraid of objects which can make a loud noise or which they think will make a loud noise. They are often afraid of objects which make a noise which they perceive to be loud, but is not actually very loud, such as ceiling fans.