Bibliography:

http://www.physics.org/article-questions.asp?id=54

http://web.mit.edu/2.972/www/reports/speaker/speaker.html

http://www.centerpointaudio.com/howspeakerswork.aspx

http://www.explainthatstuff.com/loudspeakers.htm

https://animagraffs.com/loudspeaker/

http://www.soundproofingcompany.com/soundproofing101/what-is-sound/