Introduction: Electromechanical Transducer Out of a Polystyrene Conical Section!

Picture of Electromechanical Transducer Out of a Polystyrene Conical Section!

"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.

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.

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!

Step 3: Materials

Picture of Materials

Be sure to read the end of this section where I explain alternatives and where to obtain these items.

Items for the Speaker

1 Plastic cup
4 5/16" round x 1/8" thick disk neodymium magnets
40 inches of 16 gauge enamled copper wire
Super glue (thick "gel" type works best)
Signal source with audio wire


Wire snips or heavy scissors to cut the wire
Sand paper or a sharp edge
Something pointy
AA battery (or a round object of similar thickness)

A good hook up to a signal source may be the most difficult item to obtain. If you're careful you can strip the wires out of old head phones so that your speaker can be plugged into your iPod. You can buy speaker wires that have a plug on the end and are bare on the other to plug into a radio. I used the bared ends of sound wire running out from an old TV. They don't need to be soldered to your speaker (unless you want to) as long as they are bare and you can twist/hold/tape to make a good connection.

Just about any size of plastic cup will work. And it doesn't necessarily have to be plastic. Real speakers use paper, silk, composites, etc. Experiment with paper plates, ice cream containers, Styrofoam cups... anything that is flexible and has a slight cup shape to magnify the sound.

The magnets don't have to be exactly 5/16" round or 1/8" thick. I used 8 5/16" round x 1/16" thick ring magnets. Just be sure that they are a good, powerful magnet that is smaller in diameter than the AA battery.

Enamel wire, also called magnet wire, is copper wire that is coated with a thin layer to prevent it from shorting. Buy it or strip it out of an old speaker for free. It doesn't have to be exactly 16 gauge... just a nice size to work with.

Step 4: Safety

Super glue can cause skin irritations. Take care when using it. If it comes in contact with your skin be sure to flush with water. If you have a known allergy to super glue, try an alternative such as small dabs of hot glue or simply using tape.

Rare earth magnets are extremely powerful! And they can wreck electronic things like your favorite mp3 player. Be careful where you place the magnets (near your digital camera... a big no no) and don't let them snap together to quickly. They may break or pinch fingers.

Shock Hazard Never attach your speaker to the signal source while it is powered on. Never touch the bare connections while the power is on.

This involves some sharp tools to cut wires and poke holes. Never hold the point or edge toward your body when making holes.

Step 5: Voice Coil

Picture of Voice Coil

Use wire snips to cut a 40 inch length of 16 gauge copper wire. Leaving a 5 inch tail, wrap the wire around a AA battery (or similar sized object). Make 14 to 16 wraps total. It is important to make as tight and neat of coil as possible.

Tip - Wire crinkly, bent and hard to work with? Pull the wire tight with both hands and run gently over a sharp edge to straighten.

Technical Terms - This coil will serve as our electromagnet. In speaker terms it is called a voice coil.

Step 6: Secure the Coil

Picture of Secure the Coil

Carefully slide the coil off the battery and secure with a couple small pieces of tape.

Very important step To get a good connection between the speaker wire and speaker, the enamel insulation has to be removed from the two tail ends of the coil. With a piece of sandpaper or the edge of a shape knife, gently scrape the coating off the tail bits of wire on the coil

Step 7: Coil to the Cup

Picture of Coil to the Cup

Use something pointy, such as a paper clip, to poke a small hole near the base of the cup. Set your coil in the cup and slide the wire tails through the hole.

Squeeze the super glue into a small circle in the center of the cup. Press the coil onto the glue and hold for ten seconds.

Split your magnets into two groups. Hold one group against the outside of the cup right under the center of the coil. Toss the second group in the cup so they attach in the center of the coil to the magnets on the outside.

Step 8: Finish Up

Picture of Finish Up

A piece of tape will hold your speaker in place. With the power off, attach the signal source to the speaker by taping or twisting. Be sure that the two wires do not touch each other at the bare connections.

Power up and rock on.

For further experimentation try different size cups, better glue, different materials, larger magnets, and different connections. This is an ugly utilitarian build just to show off the basic construction principles. But go ahead and knock yourself out making it good looking. Build a iPod speaker that looks like an old phonograph, build a giant sub woofer, or build a whole home theater system using decorated cardboard boxes for speaker cases. Go nuts you mad scientist you. Best of luck!


spark master (author)2011-09-16

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.

artworker (author)spark master2013-08-11

Nice idea! I will remember that for a very long time!

argha halder (author)2013-08-10


iudom (author)2013-04-23

Very interesting. Source: University of Nigeria

Laisseraller (author)2012-11-08

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?

c0rtx (author)2010-11-25

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

gomjabar (author)2008-04-03

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)gomjabar2008-04-11

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.

aplauche (author)Bookburn2009-06-14

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.

rocketman221 (author)gomjabar2008-08-04

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

beaulingpin (author)gomjabar2008-05-22

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

Mandela (author)2009-05-13

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

pyroten (author)2009-05-13

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)

PKTraceur (author)2008-12-17

What is magnet wire? Im attempting a Faraday AC generator. but cant find any 'Magnet wire"

pyroten (author)PKTraceur2009-05-13

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

ProphesyOfWolf (author)2009-04-26

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

cyberpageman (author)2009-01-18

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 which shows how that can be done.

steadmanjon (author)2008-04-27

This actually worked. I used an empty peanut can and some alligator clips. The sound was very weak, but I could hear it.

chriskarr (author)steadmanjon2008-11-28

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!

chriskarr (author)2008-11-28

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!).

Alexizupinhea (author)2008-08-15

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

killerjackalope (author)2008-08-04

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

TheMadScientist (author)2008-03-28

could this quite possibly be made out of an expanded polystyrene conical section as well? :D WOOT, FOAM!

Derin (author)TheMadScientist2008-06-22

eh...directional (read:padding) but it would work wonders

Bookburn (author)TheMadScientist2008-03-31

The first one I ever laid my eyes upon was just such a conical section.

Bookburn (author)2008-05-23

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 (author)Bookburn2008-06-13

Would a resistor help with cutting down on the current?

Bookburn (author)bliz232008-06-14

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.

Wareagle (author)2008-02-03

wow..... this is pretty cool.

Kiteman (author)2007-10-22

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)Kiteman2007-10-22

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!

Kiteman (author)Bookburn2007-10-23

Thank you. Normally I would tell them that myself, but I have a policy of opening Science Club to all interested children (the only qualification is good behaviour), and this year I seem to mainly have kids with plenty of enthusiasm but little actual ability (we made simple wind turbines recently, just paper and glue, and only about half even turned...)

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...

Bongmaster (author)Kiteman2007-12-12

Now thats a kool tube :)

fade400 (author)2007-11-29

excellent. I'm going to recreate this as soon as I get some magnets. I was wondering however, did you achieve the best sounding speaker from the plastic cup or were you able to find a better material ? By better sounding, I mean better sounding in terms of music not random sounds. Thanks

rimar2000 (author)2007-10-18

Maybe I don't know explain myself: when I speak of polarity I refer each imam of the stack, not the electric current in the coil. I think that 2 imams of 1 gram there are not the same thing as 1 imam of 2 grams. When there are 2 or more imams, the poles interacts and cancels partially themselves. Nevertheless, I believe Bookburn when he says "More was definitely better (because they produced a stronger magnetic field)".

rimar2000 (author)2007-08-09

Excellent instructable.

Doesn't it care polarity with which the imams are heaped?

I believe that the device would improve a lot putting a single magnet on each side of the plastic membrane, with the poles appropriately guided.
Being two magnets, "proves and error" is the easier form of aligning them.

Bookburn (author)rimar20002007-08-09

Polarity doesn't matter. Hooked in one configuration the electromagnet and permanent magnet will pull towards each other, and in the other they will push away... but they will always do so in the same frequency. The vibrations make the same sound no matter what direction it is in. Consider a perfectly flat speaker. The sound in front of the speaker is the same as the sound coming from the back of the speaker even though the speaker is vibrating in a different direction relative to the listener. But I have to admit that it would be cool if the sounds were played backwards in the back of the speaker and you could hear satanic messages in reruns of "Everybody Loves Raymond" just by sitting behind your TV. I tried a number of different configurations for magnets. More was definitely better (because they produced a stronger magnetic field). And slightly behind the coil was better than slightly in front. Try it just holding the magnets behind the bottom of the cup so that they are not actually attached to (weighing down) the moving diaphragm.

rimar2000 (author)Bookburn2007-08-09

Thanks for your response. I continue thinking that the polarity yes, it cares. The vibration is made of movements toward "behind" and "advance". The movement cannot be the same one if the attraction of an magnet is canceled total or partially for the repulsion of another. Also, it is present the topic of the mass: the ideal thing would be a membrane of mass zero. More magnets we added, more we move away from that ideal. I hope to have some free while to make some tests, the idea is very good. And also, cheap! Pardon my English, I speak spanish. I use

bookburn and killerjackalope are correct but you rimar are not. polarity only matters when you make more than one speaker and then only that they are the same for both. and even then its not that much. it has nothing to do with the attraction of the magnet being canceled. the magnet is not canceled just pushed or pulled both work to do the same task in this experiment. the signal that causes them to work is AC alternating current that means that it will switch polarities as it goes causing the coil to push-pull-push-pull to the frequency of the source that in turn vibrates the cup. it does not matter which sequence comes first the push or the pull. you probly think it matters due to the polarity written on the leads to speakers and that has to do with when you have more than one. secondly as bookburn has already stated the more magnets the stronger the field. the stronger the field the stronger the vibration. yes more magnets way more but the strength of the vibration increase is likely stronger then the increase in load. by the way: very nice post I like when people take the time to put the science into their posts even when I already know it.

killerjackalope (author)Bookburn2007-08-12

the sound isn't going backwards at any point its a vibration as such so behind the speaker has the exact opposite vibration but that sounds exactly the same but if 2 identical speakers were line line and the fronts were both pointing in the same dierection the forwards and backwards would cancel eachother out somewhat because the backward bump hitting the exact opposite bump makes a zero bump if ya get me its how noise cancelling earphones work (the active ones that have a little box witha mic on it)

Kiteman (author)2007-09-22

If I click on the "singing plant" link in the text, it takes me to the edit function!

Bookburn (author)Kiteman2007-09-22

My apologies for the disappointing link... I think I have it fixed now.

Bookburn (author)Kiteman2007-09-22

Sweat Moses! That's not right at all... It's supposed to be a link to the movie "Little Shop of Horrors"! I suspect foul play.

killerjackalope (author)2007-08-12

theres transverse and lateral waves i think these are lateral that go back and forth but i can't remember right know

Kiteman (author)killerjackalope2007-09-22

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.

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