Websites on Acoustic Phonetics and General Acoustics

Acoustic Phonetics

Praat - A speech analysis program (for just about any platform), created by Paul Boersma and David Weenink.
Monthly Mystery Spectrogram Website - Includes several good examples of spectrograms and a brief tutorial on how to read them. There haven't been any new mystery spectrograms posted in a while, but there is an archive of old ones, presented with detailed segment-by-segment commentary. Maintained by Robert Hagiwara.
Speech Analysis Tutorial - Includes waveform and spectrograms for the word phonetician. Created by Marcus Filipsson.
Sound Waves - The first page in a series of course notes on acoustic phonetics, from a course taught by Kevin Russell at the University of Manitoba. You may recognize some of the diagrams from Rogers's textbook.
Spectrogram Reading - A tutorial by Tim Carmell, Andrew Cronk, Ed Kaiser, Richard Wesson, Johan Wouters, and Xintian Wu. Their spectrograms use colour, rather than just shading, to indicate intensity.

Sine wave applet - Displays two sine waves (editable by the user) and their sum.
Sound Waves and Music - A tutorial from The Physics Classroom. Contains basic information about the properties of sound waves, with good illustrations. Written by Tom Henderson.
Handbook for Acoustic Ecology - Contains definitions and illustrations for a wide range of acoustic terminology. Edited by Barry Truax.