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"A what?" you ask. An "electromechanical transducer" refers to the type of speakers we are most familiar with; a permanent magnet and an electromagnet wildly vibrating to produce sound. And by "polystyrene conical section" I mean plastic cup.
Whatever this is, it is not an Instructable on how to callously rip apart your roommate's computer speaker and glue the driver into some other object. I show how to build the actual transducer unit (commonly called a speaker driver) with a few simple objects. The speaker is super easy, extremely impressive, and so cool that it even makes Kenny G. sound good.
If you are abhorred by reading, feel free to cut to the meat of the how to on step 3. But the theory I present in the first few pages may help you build a better speaker, and... (dramatic pause)... may even make you smarter (Egad!)
There are a couple risks (other than learning) so please read the Safety Page.
Whatever this is, it is not an Instructable on how to callously rip apart your roommate's computer speaker and glue the driver into some other object. I show how to build the actual transducer unit (commonly called a speaker driver) with a few simple objects. The speaker is super easy, extremely impressive, and so cool that it even makes Kenny G. sound good.
If you are abhorred by reading, feel free to cut to the meat of the how to on step 3. But the theory I present in the first few pages may help you build a better speaker, and... (dramatic pause)... may even make you smarter (Egad!)
There are a couple risks (other than learning) so please read the Safety Page.
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Signing UpStep 1Theory: What is Sound
The first concept to wrap your rubbery little mind around is the idea of sound. Sound isn't an object. Your boom box isn't firing little particles of magic sound dust to tickle your ears with M.C. Hammer. Instead, sound is the transfer of energy.
A source (such as the speaker on you boom box) is receiving electrical energy and converting it into mechanical energy. If you'll kindly place your fingers against your throat and scream the phrase, "someone's already made a movie about a giant singing plant," you'll feel that mechanical energy in the form of vibrations. You'll also have noticed those vibrations when you stand really close to a drum set or those cheap speakers your ex-girlfriend blasts Smash Mouth on.
That mechanical vibration acts like a piston pushing particles forward when it moves outward and pulling particles backwards when it pulls in. Like I said, sound isn't an object; it is a transfer of energy. Those particles are not hurling towards your ears. The first particle touches the next particle and moves it a bit. That particle moves the next particle a little bit, and so on until that movement, that energy, reaches your ear. How fast those particles transfer energy (the speed of sound) is determined by what type of particle it is. In air, sound moves at 343 meters per second. In your secret underwater sea lab it moves at 1533 meters per second (I won't tell anyone).
I know you implicitly understand this, because you're super smart, but small sources move a small number of particles and big sources move a big number of particles. If the mechanical vibration is small (if the piston only moves a short distance), it doesn't transfer much energy to the particles so the sound is small. If your speaker is really athump'n (the piston moves a large distance) it is transferring large amounts of energy and it produces large sound.
One last note on the concept of sound, we say sound is a wave. But it isn't one of those up and down waves like a jump rope or those sine graphs your algebra teacher makes you draw. It is a back and forth sort of wave featuring a series of particles pressed really close together and particles spread far apart. If you stretch a good slinky out on the ground and give it a push (a push not a wiggle! a push I said!) you'll see another example of this type of wave.
A source (such as the speaker on you boom box) is receiving electrical energy and converting it into mechanical energy. If you'll kindly place your fingers against your throat and scream the phrase, "someone's already made a movie about a giant singing plant," you'll feel that mechanical energy in the form of vibrations. You'll also have noticed those vibrations when you stand really close to a drum set or those cheap speakers your ex-girlfriend blasts Smash Mouth on.
That mechanical vibration acts like a piston pushing particles forward when it moves outward and pulling particles backwards when it pulls in. Like I said, sound isn't an object; it is a transfer of energy. Those particles are not hurling towards your ears. The first particle touches the next particle and moves it a bit. That particle moves the next particle a little bit, and so on until that movement, that energy, reaches your ear. How fast those particles transfer energy (the speed of sound) is determined by what type of particle it is. In air, sound moves at 343 meters per second. In your secret underwater sea lab it moves at 1533 meters per second (I won't tell anyone).
I know you implicitly understand this, because you're super smart, but small sources move a small number of particles and big sources move a big number of particles. If the mechanical vibration is small (if the piston only moves a short distance), it doesn't transfer much energy to the particles so the sound is small. If your speaker is really athump'n (the piston moves a large distance) it is transferring large amounts of energy and it produces large sound.
One last note on the concept of sound, we say sound is a wave. But it isn't one of those up and down waves like a jump rope or those sine graphs your algebra teacher makes you draw. It is a back and forth sort of wave featuring a series of particles pressed really close together and particles spread far apart. If you stretch a good slinky out on the ground and give it a push (a push not a wiggle! a push I said!) you'll see another example of this type of wave.
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Check these animations to see the difference.
After extensive testing with a senior physics class, long discussion with my physicist friend and an old boss (who's an electrical engineer by trade); I've found that I have a few things wrong about the coils.
The impedance in the coil I recommend is extremely small; and, according to ohms law, that results in a massive current draw. I was really having troubles finding a power source that would work with my class (most would trip their internal relay switch because of the current draw if I attempted increasing the volume). The solution is to create larger impedance (and resistance) by adding more coils. I have not found an optimal number yet - but I recommend at least 50 wraps of 22 gauge wire or smaller.
The direct result is that you can crank up the stereo louder and get much more sound out of the cup. But this is not without cost. I attempted 100 coils of 32 gauge wire and was really enjoying the results. And as I sat there holding the cup up for sixth graders to see, I was cranking up the volume on my stereo (just to see how high I could take it), when the coil melted through my cup in a great smoky cloud.
Suspending the coils with another cup (as many commentators have suggested) also makes considerable improvements to the sound output (though I am still partial to the simplicity of a one cup system). I hope to continue improve the design and, later this summer, rewrite the whole instructable (including new photographs) for people.
In conclusion - I strongly recommend more coils in a smaller gauge wire. Not so many that it heats up and melts things (or worse - burns you), but more just the same. Thank you everyone for all the feedback (including the nit-picky ones).
If these work, I have a half-warmed idea to make a short Ruben's Tube with the speakers, but I'm still persuading my Head of Department that that would be safe...