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Electromechanical Transducer Out of a Polystyrene Conical Section!

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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.
 
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Step 1: Theory: 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.
if the wire is short length place on a flat work table place a plank over it and roll it back and forth(like a rolling pin motion). You will preserve the insulation and it gets it very straight. Use this for making darts on job site. worked well.
Nice idea! I will remember that for a very long time!
argha halder8 months ago
great!!!
iudom12 months ago
Very interesting. Source: University of Nigeria http://www.unn.edu.ng
Great post! I have changed the setting for my computer speakers to sound like an auditurm but forget how ot change it back got any suggestions?
c0rtx3 years ago
i wonder if anyone knew that you can use this same principle in reverse to generate electricity, its called thermo acoustic power....heat directly to electricity, the only moving part is the plastic membrane at the end of the cone(heat expands gas creating a pressure wave flexing the membrane with a coil, a pressure wave in gas is also known as sound, hence thermo acoustic) russians used the technology to power radar stations off kerosene room heaters durring the cold war
gomjabar6 years ago
As with many instructables the terms "a few household items" or your "simple objects" leave a lot to the imagination. 5/16 round 1/8" thick disk neodymium magnets and 40" 16 gauge enameled wire are not exactly "simple objects". That is to say things I just have laying around. How about a small portable particle accelerator? Maybe all I have is a 5/16" round 1/8" thick disk sumarium or cobalt magnet. Don't say "simple"!
Bookburn (author)  gomjabar6 years ago
Dear Gomjabar, Thank you for your concern. Your attention to detail certainly makes this world a better place. Feel free to pull your "small" portable particle accelerator out of your rear and use it in your speaker build.
LOLOLOLOLOLOL this just made me laugh anyways good instructable although the speaker works better if the solid state magnet is not directly linked to the vibrating part of the plastic cup.
i have high power neodymium magnets and lots of magnet wire laying around. doesnt everyone
I do
HDD magnets and magnet wire out of crt monitors
Who doesn't have magnets and wire? Hell, you could even cut up one of those flexible magnets (like the "support our troops" ribbon magnets people put on their cars) into little disks and stack them. As for wire, this could be any thin wire. Granted, you get the best result from wire without plastic insulation (as they reduce the number of coils you can make in the closest area to the magnets), but any wire will create a flux that acts in the magnetic field. So hey, don't complain. And anyway, it's really easy to make a particle accelerator too. Get a longitudinal spring and a ball that has a diameter greater than the diameter of the spring, and use the spring to accelerate that particle. It's not as nice as the accelerator I work at, but it fits the definition. but anyway, without imagination, even following instructions are too hard for some people
Mandela4 years ago
Nice explanation and pictures ! (maybe you dont have to write the explanation, just show the images!) :P Confused still with the sound source.. Would you show the images from the sound source? (like from ipod) Requesting electric guitar amplifier :P
pyroten4 years ago
great i'ble just thought i'd point it out in step 2 paragraph 2 line 6 last word u spelt "bass" like "base" but gud wrk (Y)
PKTraceur5 years ago
What is magnet wire? Im attempting a Faraday AC generator. but cant find any 'Magnet wire"
magnet wire is i believe just a strand of copper wire in different gauges that is coated in a thin sometimes thick protective clear layer which does not interfere with a magnetic field. sometimes it comes under enameled wire i think
Trippy! I made one of these in like 5 minutes. As previously said, the sound was weak. But it was definitely there! Good instructable =P
There is a design problem with this plastic cup speaker. The magnetic field from the coil has to move the heavy mass of the permanent magnets to produce sound. The magnets shouldn't be touching the plastic cup. Check out http://www.instructables.com/id/Homemade-speaker/ which shows how that can be done.
steadmanjon5 years ago
This actually worked. I used an empty peanut can and some alligator clips. The sound was very weak, but I could hear it.
Well... ...the whole superglue in a plastic cup thing worries me. If the cup is made of the wrong kind of plastic, the super glue will dissolve it. Please test the cup first!
chriskarr5 years ago
Not a SHARP edge, as in one that could be used to cut something but, instead, something soft, like wood, with a bit of an edge to it (like the edge of your mom's coffee table!).
I just wanted to say that I have found this instructable very informative and the comments and chats below have truely opened my mind to all sorts of thinking. I know it sounds corny... but I hope I can design and create a very effective... efficient... quality... long lasting speaker for under $2-$5
theres transverse and lateral waves i think these are lateral that go back and forth but i can't remember right know
Transverse waves go side-to-side (the traditional sine wave). Sound waves are longitudinal - they vibrate back and forth in in the direction the wave is travelling.

Check these animations to see the difference.
thats alright then I just couldn't remember sorry my physics teacher called them lateral as she was a twit, seriously during the energy transfer experiments I tricked her into letting me smoke in class
(removed by author or community request)
Don't even start. I'm really really tired of this one. Go annoy someone else, please.
I'm sorry
Thank you for stopping...
My pleasure
could this quite possibly be made out of an expanded polystyrene conical section as well? :D WOOT, FOAM!
eh...directional (read:padding) but it would work wonders
Bookburn (author)  TheMadScientist6 years ago
The first one I ever laid my eyes upon was just such a conical section.
Bookburn (author) 5 years ago
Major Update

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).
bliz23 Bookburn5 years ago
Would a resistor help with cutting down on the current?
Bookburn (author)  bliz235 years ago
That was my first question I asked my old boss. The answer is yes, but it wouldn't "add" anything to the speaker. More coils has the same effect of increasing the resistance PLUS it generates a stronger magnet.
Wareagle6 years ago
wow..... this is pretty cool.
Kiteman6 years ago
Regarding step 7 - does it matter if the coil is attached to the outside of the cup? I'd like to make these with my science club, and some of them have distinct manual dexterity problems.
Bookburn (author)  Kiteman6 years ago
As a science teacher, my answer to a student would be "try it and find out." But since you're a friend, no it doesn't really matter. I put it on the inside so that it looked "neater." It just needs to be attached securely to the cup so that it moves the bottom like a diaphragm. Good luck. Science clubs rock!
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