Plywood Acoustic Phone Amplifier

1 Material

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.
I used a belt sander to sand the outside of the tube because this removes a lot of material quickly. If you use a belt sander rotate the piece quickly so you don't get any flat spots.
Sand the top and bottom piece too.
Cut out a piece of the tube. I removed about 40% but anything around that number would work. The main thing is to keep the saw straight so the 2 cuts are parallel.
Next, glue the top and bottom to the tube, making sure the slot is on the correct side.
I also glued a small piece of wood onto the top to allow the phone to lean back slightly and have something to rest on.
All that's left is to add some finish and you're done!

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Have a question about this project?

3 questions
  • Ramona V
    Ramona V
    on Jan 29, 2017

    curious why you did not cut the inside of the circles first?

    • Robin Lewis
      Robin Lewis
      on Jan 29, 2017

      The hole saw has a small pilot bit in the centre that keeps it from moving while you drill. If you cut the centre part out first then you lose that pilot hole and and you'd have to manually line up the outside hole (you'd no longer be referencing off the same centre hole). I guess it would work with a drill press though, and you're right, it would make life a bit easier, but with a handheld drill this way seemed less complicated

  • Kvmjmm
    on Jan 29, 2017

    So does putting phone on to of this DIY project cause it to amplify? Say, for my elderly mom?

  • Benjamin
    on Mar 9, 2021

    I wanted to hear the sound through the finished product in the video. That was the only thing that was missing. You put the phone on the stand and touched play, why not let us hear how it turned out?...

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