Passive iPhone Amplifier

I was taken by Reid Bingham's low-tech iPhone amplifiers he designed for a workshop. Made from wood with circles of decreasing diameter cut in them, they are a perfect solution that require no batteries.

photo by Reid Bingham

I really like this project and spent some time thinking about how to lower the threshold for this project. How could I teach people to build these if they have limited woodworking skills or are meeting in a space without power tools?

I opted to use insulating foam, which is available in a 2 foot by 3 foot by 1 inch thick sheet at my local big box. I also used a snap blade knife, a cutting mat, the Windfire Designs Circle Tool and a T-square.

I sized up my iPhone and decided a four inch square piece of foam would work nicely for my first build. I cut four of these squares.

I used the circle tool to cut two circles from two foam blocks using the snap blade and the circle tool as a guide. One circle is larger than the other. The key to cutting the foam, I learned, was shallow cuts and sawing motions once the knife is deep in the foam. I shaped the circles a bit with the knife, too.

I gave the blocks a quick sanding after testing on the fourth piece of foam I ended up not using. 

Like Reid, I used rubber bands to hold the blocks together. The phone fits into a slot I cut in the third piece of foam. There is a circle cut below the phone slot so the speakers are unobstructed.

It definitely makes the phone's sound fill the room! Depending on who is in the room with me, this is a good thing or a bad thing!

I think the use of foam, while presenting challenges of its own, does lower the threshold for this project. People who might be unfamiliar with working with wood can gain fluency using a knife and experimenting with subtractive fabrication. A foam cutting hot wire would be an interesting addition to the tools, at least for the straight cuts, and would provide a cleaner finish. There is nothing keeping the shapes from being more than square, either! 

I coated the foam with two layers of spackle that included primer, allowing it to dry between coats and sanding, too.

Afterwards, I used a quality spray paint with built-in primer and gave the amplifier a nice, even coat of paint.

After letting the under coat dry, I used a crappy black spray paint to give it a second light coat of paint. This provided a great oxidized look with the aluminum colored paint underneath.

Vinyl feet finished off the amplifier and made the model seem "lighter" by elevating it slightly off the table.

I was really happy with how this project turned out. I think it is very scalable: anyone you can trust to use a knife can build one of these. Give this idea a try and let me know how it goes.