Simple Speaker


I don't know who invented this nifty speaker, but it sure is cool! Tobin Hahn, a high school physics teacher showed it to me. This project has a lot of room for improvements and experimentation. One thing to note however, is DO NOT HOOK THIS SPEAKER UP TO A NICE STEREO! You will need a sound source that is not going to make anyone cry if it blows. More details on this below.

As you can see, we aren't talking high fidelity here. But it does make sound! It has got to be the simplest speaker around.

Materials required (per speaker): 1 plastic party type cup, 22-30 gauge magnet wire (see below), magnets (see below), electrical tape.

There are a couple of variables here, depending on what gauge of wire you are using and what sized magnets you have. The magnets I use are doughnut style, and measure 1 1/4" in diameter and are 1/4" thick. These are perfect, but other magnets will work. The main thing is that the magnet should be smaller than the coil, which should be smaller than the end of the cup. I used Solo brand cups, and a 1 1/2" coil fits the indentation on the bottom of the cups perfectly.

I looked around until I found a cylinder that was 1 1/2" to use as a form to wrap the coil on. In my case the form was a bottle of graphite lubricant. There is a wide range of gauges and number of turns that will work here. I have used as few as 5 turns of 20 gauge wire, and as many as 50 turns of 30 gauge wire. I would recommend using between 22 and 30 gauge wire with between 20 and 30 turns. Use what you have and experiment.

Once you have made the coil, slip it off the form and tape the ends. It's easier to cut the tape beforehand!

Once you have completed the coil, it's time to attach it to the bottom of the cup. I use hot glue, but tape or other glue will work. Then stretch a piece of tape tightly over the end of the cup (see below why). Place a magnet on top of the tape, centered over the coil. Put a piece of tape over the magnet. The pictures below show this sequence.

    

I only tape one magnet on to the speaker. This way I can add more magnets easily by simply letting them stick to the first magnet.

OK, your speaker is done. Now you need an audio source. Old radios or tape decks will work and are easy to come by. Older stereos will work, but newer ones seem more sensitive. I wouldn't try a portable CD player. The main concern is to use a sound source that won't make anyone cry if it blows. I foolishly tried a Simple Speaker on my home stereo, and it immediately tripped an internal breaker. Fortunately it reset itself and the stereo still works.

Once you have found your audio source, you need to connect your speaker to it. What you need here depends on what you have for an audio source. Find the output jack. You need to get a plug that fits this jack. It is a good idea to bring the audio source with you to buy the plug if you can. Once you have the correct plug, connect it to your speaker. Then plug it in and crank it up!

It is suggested that you limit periods of listening to your speaker for to a few minutes at a time. The transistors in the amplifier will tend to get hot and will burn out eventually.

How does it work? Whatever you are using to supply the audio input sends an electrical signal to the coil on the speaker. When this electrical current flows through the wires, it creates a magnetic field. This field interacts with the field of the magnet, making the coil move as it is attracted and repelled. Since the coil is glued to the cup, the cup is moved as well. The moving cup moves the air, which creates the sound. When we use the cup like this it is called a diaphragm.

For more information on how the speaker works click HERE.

Why the first piece of tape? Ideally, we would like the magnet to mounted so securely that it cannot move when it is interacting with the magnetic field of the coil. If it isn't, the magnet will move as well as the diaphragm, wasting energy. This means we get less volume. That is why we put the first piece of tape on the cup, to provide support for the magnet. The speaker will work even if you tape the magnet directly onto the cup, but once again you will get less volume.

Possible improvements: Anything that can be done to stabilize the magnet will improve performance. A popsicle stick perhaps? Stronger magnets help a lot. One of the design flaws of the Simple Speaker is that the magnet is relatively far from the coil. This means the magnetic fields are not "coupling" as well as they could. Making a coil that the magnet just fits inside of, perhaps wrapped on a toilet paper tube would help immensely I'm sure. The trick there would be to attach the magnets. And a party cup isn't the only diaphragm in the world. Tupperware springs to mind, and all sorts of plastic containers would work. If you devise any cool versions, e-mail me!