Cutting and sawing

You have 7 12x300mm wooden dowels, right?

Cut one of them in three equal parts - making each stick 100mm long. Leave the other six sticks as they are for now.

Grab one of the printed speakers. Now, you'll need your knife - shave off the top 1cm of each stick. Shave it down to a diameter of 10mm. Keep testing if the stick fits into one of the supported holes in the speaker - with a little bit of force, but be gentle not to break the speakers layers.

You'll now have 9 legs with a nicely cut top.