You may have seen these in the Make Blog. This is how to make your own.
Step 1: The Finished Speaker Box
This is the finished article. In this case the box is an 80mm cube but it could be any size you like just choose the card thickness to suite the size of the box.
Although this was made from card you could just as well use polypropylene as a harder wearing material, you can often buy stationary folders made from polypropylene that you can recycle.
Step 2: The Net for the Crash Lock Box
This is the net for the crash lock box. You can scale it up or down but keep the same proportions. The example Illustrate here fits onto an A4 sheet of card to give an 80mm box. Punch through the holes to let the sound out. The tab at the right hand side is fastened with a couple of brass paper rivets. The rest simply locks together. You may want to make other suitably sized holes if you need to fit a speaker jack socket.
Step 3: Cut Out and Speaker Fitted
The net has been cut out and the speaker fitted - I used hot glue on the rim of the speaker. The tab is attached to make up the basic box. The bottom crash lock is assembled and only the top has to be closed. To reduce cost I didn't bother with a speaker socket but ran wires directly to the speaker connections.
Step 4: Last Step
Closed the bottom and you are finished. The crash lock mechanism ensures the box stays closed until you need to fold them flat then you can pull the flaps out and fold the box flat. You can leave the speaker inside and as in the originals keep them in a plastic bag until required again. The surface can be painted or you can glue the wrapping paper from your last birthday present onto the box to jazz it up.
Even a simple test shows an improvement to the sound from a very small speaker. A bigger speaker will sound better.