http://www.bsharp.org/physics/stuff/guitar.html
http://www.aip.org/radio/scripts/guitar_physics.txt
http://www.aip.org/radio/html/guitar_physics.html
http://www.phys.unsw.edu.au/music/guitar/
http://ffden-2.phys.uaf.edu/211.web.stuff/billington/main.htm
http://www.physicsclassroom.com/mmedia/waves/gsl.html