A crash box is a device which reproduces a crash or collision sound effect. Commonly used in theatre, they consist of a large metal or wood crate in which glassware, china crockery, wood blocks or other delicate objects are placed. The items may or may not be broken.
In theater, a crash box is an apparatus that reproduces the sound of a collision by using a large crate filled with breakable items like glassware, china, and wood blocks. The objects within may be undamaged or deliberately broken to create realistic effects.