Why r magnets used in speakers...?

I have a full description of how they work and why they're used but to simplify things and allow you to see the animations and all, I'll just direct you to http://electronics.howstuffworks.com/speaker4.htm this site gives you a detailed and thorough explanation to why magnets are used in speakers. I fancy you'll be able to build your own speaker after you read it.:)
Hope that helps.