What are the main differences in sound and construction between a xylophone, marimba, vibraphone, and glockenspiel?

The main differences between a xylophone, marimba, vibraphone, and glockenspiel lie in their sound and construction. The xylophone has wooden bars and a bright, sharp sound. The marimba has wooden bars as well, but they are larger and produce a warmer, mellower sound. The vibraphone has metal bars and a pedal mechanism that creates a vibrato effect, giving it a shimmering sound. The glockenspiel has metal bars like the vibraphone but is smaller and produces a bright, bell-like sound.