Concrete Bluetooth Speaker

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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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    6 Discussions

    2
    None
    digdug18

    Question 18 days ago

    How does this sound? How heavy is heavy?

    Anything you would revise for a second version?

    1 answer
    0
    None
    techydiydigdug18

    Answer 15 days ago

    It sounds ok for a low power amplifier / speaker combo. It doesn't vibrate or resonate.
    I haven't weighed it but about the same as couple of bricks.

    The first version I made with a removable inner mould pipe, before realising that keeping the inner pipe inside was a good idea and much easier.
    The second version I tried drilling holes for the switches, that proved to be very difficult.
    The things that I would revise are that the outer pipe didn't need to be cut in half, one cut would do. I did this originally because I was going to cast the switches directly in the concrete.
    I would also install a higher power amplifier/speaker combination and better bluetooth module, the frequency cutoff from the cheap ones is about 16Khz.
    I would install mounting threads ( rivnuts or similiar) on the inner pipe before casting the concrete.
    I had also intended to extend the module leds. The speakers are transparent, so the leds could act as backlights.

    0
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    David Hoskins

    15 days ago

    Why make it battery powered if it's not portable? I'd think powering it from a 3v or 5v wall wort would be easier/cheaper/simpler?

    1 reply
    0
    None
    techydiyDavid Hoskins

    Reply 15 days ago

    Several reasons:
    1. It is portable despite being heavy, it was originally intended to be used outside.
    2. Where it is currently located is not near a power point.
    3. Solar charging.
    At the end of the day it was an experiment, people can take whatever they want from it.