Experiment with a haptic (touch) feedback interface by building your own "tactor" (tactile stimulator). Although commercial tactors cost hundreds of dollars, this one (Fig. 1) can be built for under ten dollars.
Submitted by Ace Monster Toys for the Instructables Sponsorship Program.
Step 1: Make Holes in the Speaker Cone
Since we are making a tactor, we want the voice coil to move as freely as possible, and make as little noise as possible. The answer is to perforate the loudspeaker cone (see Fig. 2). This can be done using the fine tip of a soldering iron, or the tip of a small brass rod heated in a flame. Do NOT use a screwdriver or any magnetic material, since there is a strong magnetic field around the voice coil. Disregarding this advice leads to the sort of results shown in Fig. 3.