This was an experiment to create a Bluetooth speaker with a cast concrete case.
Concrete is easy to cast and it's heavy, ideal for speakers, probably not for portable speakers, but this one sits on a bench and never moves.
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Step 1: Make the Concrete Mould
I made a mould to cast the concrete tube that forms the body of the speaker.
The outer part of the mould is a length of pvc underground drainage pipe.
The inner part is cut from pvc gutter downpipe.
These two pipes are mounted vertically to form the mould.
The base of the mould is cut from wood and a plastic chopping board.
The circles were cut with a circle cutter / fly cutter drill attachment.
Holes for the switch and power connector were formed by using a wooden dowel and plastic pipe of the same diameter.
Nuts were cast into the concrete to form attachment points.
Step 2: Cast Concrete
The concrete was made with extra rapid cement and ballast with a 1:4 mix ratio.
I didn’t want the larger stones in the mix, so I removed them with a garden sieve.
You can also use normal Portland cement or premixed dry bagged concrete instead.
The concrete was tamped down with a piece of dowel to remove any gaps
I also used an electric sander to vibrate the sides of the mould which helps liquefy the concrete so that it can move around in the mould and releases the air bubble from the mixture. This helps give a much better result.
Concrete cures rather than dries, so its important to keep it slightly damp until it has fully hardened.
Step 3: Make a Stand
To make the stand I cut two end pieces from an offcut of plywood.
These were spaced apart with two lengths of stainless steel threaded rods and nuts.
The concrete tube simply sits on top.
Step 4: Electronics
The electronics are pretty simple, consisting of a bluetooth amplifier module, a tp4056 charger module, 18650 battery, a switch and a power socket.
The easiest way I could think of mounting the modules was to create a wooden holder.
Step 5: Assemble the Speaker
The electronics assembly was mounted in the concrete tube.
The switches were a simple friction fit inside the cast holes.
The speakers were glued to the wooden rings and then bolted to the concrete tube, using the nuts that were cast into the concrete.
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