1. http://blake.prohosting.com/pstutor/physics/wave/wave_concept.html
2. http://th.wikipedia.org/wiki/%E0%B8%84%E0%B8%A5%E0%B8%B7%E0%B9%88%E0%B8%99
3. http://www.bs.ac.th/lab2000/physicweb/sonic.htm
4. http://www.icphysics.com/modules.php?name=Content&pa=showpage&pid=54
5. http://web.ku.ac.th/schoolnet/snet3/saowalak/wave/wave.htm