http://th.wikipedia.org/wiki/%E0%B8%84%E0%B8%A5%E0%B8%B7%E0%B9%88%E0%B8%99
http://www.rmutphysics.com/physics/oldfront/88/wave.html
http://www.icphysics.com/modules.php?name=Content&pa=showpage&pid=54
http://www.rsu.ac.th/science/physics/pom/physics_2/wave/wave_1.htm
http://www.bs.ac.th/lab2000/physicweb/sonic.htm
http://www.marine.tmd.go.th/wam.html