An acoustic amplifier is a bit of a misnomer; the sound isn’t actually amplified but rather all of it directed in one direction, making it appear louder. This is a simple project that takes advantage of that principle and is achieved with some basic wood working tools.
Start by using a hole saw and cutting all the plywood discs. You can use any thickness of plywood but the thicker the plywood the less pieces you’ll need to achieve the height you want. My final height was 150mm so I used 6 pieces of plywood. I used a 100mm hole saw for the outside diameter. This gave a pleasing height to width ratio.
Once you have cut the outside diameter, cut the inside. I used an 70mm diameter hole saw for this. It gave me a 15mm thick wall and I wouldn’t want to go thinner than that.
To find out where to hold the disc in place briefly cut the inner circle with the disc in your hand being VERY CAREFUL. This will show where you can clamp the disc. Then clamp it in between 2 pieces of wood so that the centre of the hole saw can exit the bottom of the disc and cut out the centre.
After all that you should end up with a few plywood circles. In may case I had 6.
Get these glued and clamped first because they’ll need to be sanded soon.
The top and bottom can be made of plywood, but I had some left over oak that I used to give it a unique look.
Start by lightly cutting the piece of wood with the big hole saw (the one you used above). This score will show where the centre of the disc is and this will be the guide so you can mortise out a hole for the phone. Don’t worry, that’s just a technical terms of “making a slot”.
Draw a rectangle the size of your phone somewhere on the top piece. I placed mine just in front of the centre hole. Then use a chisel cut the wood along that line.
Next, I used a router to remove the material but you could also do this step with only a chisel. You’ll need to make a shallow grove for the phone to fit in, then drill through where ever the speaker is. I created this for an iPhone so half of the groove had to be drilled through.
It should look something like this. Once you’ve made the slot you can go back to the hole saw and finish cutting through the top and bottom piece.
Now that the glue should’ve dried on the tube you can start sanding. Make sure to sand the inside of the tube now, while the top and bottom aren’t attached.
Glue and drive a dowel into the top and bottom to close the centre hole made from the hole saw.