I got inspired to make this indestructible a couple of days ago when I stumbled across a set of really nice set of audiobahn subwoofers at a yard sale. The only problem was that the speaker cones were badly cracked from the previous owner pushing to many watts through them. I bought them, took them home, and discovered a cool trick to fixing the cracks which you are about to learn about.

Disclaimer!
Don't blame me if you break your broken speaker cones lol.
This wont properly work on metal or plastic cones.
This fix will likely not make your speakers sound better than they did before they cracked. It should however sound better than they did when they were cracked.

Step 1: Required Tools

Here is what you will need to fix your speaker.
Elmer's glue, gorilla glue (this stuff also works great for fixing cracks in speaker dust covers), or another type of semi flexible wood glue
A regular coffee filter.
A paint brush. I recommend a semi stiff bristled brush as it helps to rub the glue into the speaker cone
Scissors
A plate
and last but not least a broken speaker...Duh

Step 2: Mixing the Glue.

Your first step is to water down the glue so it will properly soak into the speaker cone. Mix the glue with one part water to three parts glue. I wouldn't recommend adding any more water as it could cause the glue not to stick or make the speaker cone all soggy.

Step 3: Filling in and Patching the Crack.

Start by filling in the crack with glue and letting it dry. Depending on how badly cracked your cone is it might take several applications. Remember to get both sides top and bottom of the cone filled with glue. Next take a piece of the coffee filter and cut it to size so that it covers about a quarter inch to a half inch on every side of the crack. Try and tear the coffee paper whenever possible instead of cutting it. This helps the fiber bond to the cone better and prevent the edges of the patch from peeling up over time. now use your paint brush and glue the patch on. Apply a relatively liberal amount of glue to the top and bottom of the patch patch as well as the cone it's self. Once your done it may be a good idea to go back around and put some more glue around the edges of the patch to keep it stuck down. You can now let the glue dry. Genially you sould only need one layer of the coffee filter patch but in high wattage applications like large subs I recommend adding a second layer of the patch for safety.

Step 4: Paint the Patch (optional)

The final step is to paint the patch. This is pretty straight forward. I don't recommend adding a thick coat of paint as it could weaken the glue and/or crack the paint from the speaker vibration.