There are 6, 2 for each plate of metal on the machine. The long ones go under the center plate below the Z axis motors. They grip onto the bottom of the metal plate and do a pretty good job at reducing the noise if your printer sits on a resonant table. You could experiment with higher/lower infill (I would recommend trying lower first) and seeing how that affects the sound dampening effect. If you find that settings other than 50%/ 3 walls does better, I'd love to know :) Thank you!
Modified Geeetech Prusa i3 Aluminium
SainSmart TPU 98a