Electromechanical Transducer Out of a Polystyrene Conical Section!

Step 2 Theory: Converting Electrical Energy to Mechanical

Signal sources: 8-track player, cassette player, AM radio, mp3 player, what have you (with possibly the exception of a record player) all work on the same principle. They read a code and send out impulses of electricity, the electrical impulse transfers energy through wires to an electromagnetical transducer (speaker driver) and sound is produced. It's like ants in an anthill. The anthill is the signal source sending ants (electricity) out to a picnic (the speaker). We won't concern ourselves with the politics of anthills or explaining exactly the movement of ants. We just have to answer two questions to build a good speaker: How many ants reach the picnic in certain amount of time? And what are the ants doing at the picnic?

How many ants reach the picnic in a certain amount of time is different than asking how fast the ants go. Ants basically go just one speed. What I'm referring to is how close together the ants are. Did they come out of the anthill one right after the other? Or did they wait a couple seconds between each ant? This refers to the frequency of ants. If the ants are frequent visitors (one right after another) to our picnic (speaker) the sound produced will be a high frequency sound (high pitched) like the squeal of teenage girls... the kind of noise that shatters glass and ear drums alike. If the ants don't go by very often they are said to be a low frequency and the sound they produce is a low thumping base.

Frequency is extremely important in designing speakers. Some materials and sizes are just better for producing different sounds. You'll notice speakers that produce low sounds (sub woofers) are really big, while high sounds are made by little speakers. This Instructable only describes one size of speaker that is going to be doing its best to produce all frequencies of sound... but a better system can be made when the electrical impulses (ants) are filtered so that the low sounds go to a big speaker and the high sounds are directed to a small speaker.

Now what's happening at our picnic? Ignore the young couple that are rolling around and just focus on the ants. They are picking up bits of food right? In speaker terms the electrical impulses are producing magnetic impulses. Part of the speaker is becoming an electromagnet in a certain frequency determined by the frequency of the ants.

Holy Lorenz force Batman! How does electricity produce a magnet? Electricity and magnetism are closely related. In fact, if you spin magnets around something that conducts electricity (such as a bit of copper wire) you can produce electricity... but you knew that... you're smart, it's called a generator. The reverse is also true. If you make electricity spin in a circle (by wrapping wire into a tight round coil) it produces a magnetic field.

The signal source is reading a code and sending electrical impulses at a frequency. The electrical impulses travel down a wire to a coil of wires where it produces a magnetic field that is changing at the same frequency. To produce mechanical energy we now simply move a permanent magnet near our electromagnet. As the electromagnet turns on and off, it will be moving the permanent magnet back and forth. Back and forth, by definition is mechanical energy. If these magnets are glued down to something like the bottom of a cup, the cup bottom will be moving at the frequency sent by the signal source. You will feel the cup bottom vibrate and sound will be produced. Yeah baby!