Sound effects in theater serve dual purposes. They can make a performance seem more realistic, but they can also allow the audience to understand events happening offstage. For instance, a sound effect can let spectators know that a gun was fired, or that horses are approaching. However, effects are not important for actions or events the audience can see. For example, there is no need for a breaking glass sound effect when it is the actor's glass that falls and crashes to the floor.
Radio dramas put emphasis on sound effects, as the audience cannot see, but only listens to the story unfolding. Therefore, effects can help the audience visualize each sequence of the radio drama. Contrary to theatrical plays, sound effects on radio dramas are not limited to background sounds; they are an integral part of every scene. Effects could entail the main character slamming the front door or a train approaching in the background.
Most effects imitate sounds, such as a gunshot, rainfall or a crackling fire, which a human cannot reproduce without props. For the creation of such sounds, producers use either specialized or everyday materials. For instance, you can imitate the sound of a body falling on the floor by hitting a cardboard box with a plastic toy club, or crinkle a plastic bag to reproduce the sound of fire. Audio theatre producer Tony Palermo offers a comprehensive list of mechanical sound effects at his website, "RuyaSonic."
Effects are also used to reproduce sounds of large groups of people, such as a nightclub crowd, sporting events fans or an approaching gang. Such sound effects are not important for individual voices in the background, as either a radio drama actor or a performer off the stage can do the job. As it is time-consuming and inconvenient to gather large crowds every time they are needed, such effects are mostly recorded and reproduced at the push of a button.