Shells are most commonly used for orchestras, bands and choirs, although they can also be used in any application that requires passive sound amplification.
Shells are generally made of hard materials because they are designed to absorb as little sound as possible.
Acoustical shells were developed to focus sound outward in one direction as opposed to the ″sound in the round″ diffused from all sides of the open gazebo bandstand.
Professional architects were often employed to design them with varying degrees of acoustical success.
The Hollywood Bowl shell, based on a 1928 prototype by Lloyd Wright, has been rebuilt several times with the present structure being the fifth on that site.