The following are web sites that have material on
acoustic phonetics and the physics of waveforms.
Lecture notes on articulatory and acoustic phonetics by Michael Flynn, from Carleton College. These roughly correspond to what I've done in lecture. Especially the sections on acoustic phonetics are helpful.

Flynn's Articulatory and Acoustic Phonetics Essay
A tutorial on waves, with some information on how they combine:

http://id.mind.net/~zona/mstm/physics/waves/waves.html
Peter Ladefoged saying "heed, hid, head, had, hod, hawed, hood, who'd"

Peter Ladefoged demonstrating vowel formants
This site allows you to chose formant frequencies and listen to the vowels that correspond:

http://www.asel.udel.edu/speech/tutorials/synthesis/vowels.html