You might want to investigate some other sites on the Doppler Effect and other sound phenomenon. Here's a short list of some good ones:

1. The Soundry (lots of great sound information) - http://library.thinkquest.org/19537/
2. Also from the Soundry, listen to a sonic boom and see the resulting sound waves -   http://library.thinkquest.org/19537/java/Doppler.html
3. Explore Science's Interactive Doppler Site (a great simulation) - http://www.exploratorium.edu/origins/hubble/tools/doppler.html
4. Exploratorium's Doppler Effect Site - http://www.exploratorium.edu/xref/exhibits/doppler_effect.html
5. Some of the math behind the Doppler Effect - http://www.gmi.edu/~drussell/Demos/doppler/doppler.html
6. Fear of Physics introduction to the Doppler Effect - http://www.fearofphysics.com/Sound/doppler.html