When the applet starts up you will see red and green waves emanating from two sources in the center of a cubic box. The wave color indicates the acoustic pressure. The green areas are negative and the red areas are positive.
Rotate the box with the mouse to view it from different angles. To get started with the applet, just go through the items in the Setup menu in the upper right.
Zip archive of this applet.
Ripple tank applet.
2-D waves applet.
Version 1.5a, posted 2/2/14.