A very simple device that makes an incredible rumble. I didn't make this but I figured I'd document how the one I got as a gift was made. I hope to make a bigger one soon though.

Step 1: Find Materials

cardboard tube:
10.25" long
2.75" inner diameter
3.25" outer diameter

Plastic disc for membrane:
3.25" diameter
approx 0.5mm? like milk jug plastic?

Spring:
20" long
coils are almost 3/8" diameter

Glue able to bond plastic to cardboard

Hot glue.

Step 2: Assemble

Poke a small hole in the center of the plastic membrane (hot needle?)
and corkscrew a few coils of the spring through. Glue it in place.

Then glue the plastic membrane to the cardboard tube.

Put a bead of hot glue on the end of the spring to avoid a sharp end shaking around.

Step 3: Shake Then Paint.

Try it out by shaking. If it works, paint it and make it look awesome.

So this is how mine was made judging by how it looks. Hopefully you can duplicate it since the sound is amazing!

I intend to experiment with making a larger one in the near future. I've got a big heavy fiberglass cylinder as shown in the picture. :-D

If anyone knows about resonance frequencies and has some advice let me know since I believe that's how the dimensions are found.