Hello world! This is my first 'ible, so any suggestions / corrections would be greatly appreciated.
I've been toying around with coils of wire and little magnets, making tiny speakers for a couple of years, and finally wanted to make a decent one. This one cost me almost nothing, as everything was salvaged from old electronics The only things I had to buy were hot glue and popsicle sticks which are readily available at any craft store. So, let's get started!
Paper Plate (Must be paper)
Hot glue sticks and glue gun
(~2) magnets - I used magnets salvaged from a microwave, but others will work. The only requirement for the magnets is that they must be cylindrical. Any size magnet will do, but a bigger magnet will obviously produce a bigger, louder speaker. The two magnets I salvaged from a microwave are roughly 2 inches in diameter and 1/2 an inch thick and I stacked them on top of each other to make one larger magnet.
Magnet wire- Magnet wire is typically solid core copper wire with a very thin insulation that is meant for making coils for electromagnets, transformers, wireless power transfer circuits, and of course, speakers. I get all my magnet wire from old CRT screens. Inside every CRT, be it an old computer monitor, television, oscilloscope, ect., is a black ring which is a large coil of magnet wire wrapped in electrical tape that helps guide the electrons to their proper pixels. If you take the time to unwrap one (And it is very tedious), you will be the proud owner of a decent bit of magnet wire. Worth noting: (1) I don't believe projection style TV's have this coil, so make sure you know what you have before you waste your time disassembling it. (2) CRTs have high voltage capacitors that remain charged even after they're unplugged and can be deadly if you aren't careful taking them apart. I haven't personally been injured taking them apart, but I've had friends get thrown across the room from them. There are other instructables on this. Be careful!
Step 1: The Coil
Amplifiers usually require a specific impedance for the speakers it's powering. What this means is that we need a fairly long coil so we don't burn up the amp. The back of the amplifier should specify the rating. Many have switches to use either 6 ohm or 8 ohm speakers for example. If it does, switch it to the lower of the two, as this will save time and wire. Next comes the hard part: matching the impedance. Impedance is not the same as resistance. The resistance of a coil of wire will be the same as if it were straight, but the inductive reactance will increase which will increase the impedance because speakers use alternating current. The only important part you need out of this is that you don't need quite as much resistance in ohms as the impedance is rated for. As a rule of thumb, I typically subtract about 25%. For example, if your amp is rated for 8 ohms, you would use about 6 ohms of wire. If you decided to buy magnet wire rather than salvage some from a telvision, chances are it's labeled with what gauge it is. If you do know the gauge, you can use a wire gauge chart (http://www.powerstream.com/Wire_Size.htm) to find how long the wire will need to be to match the resistance of the amp. To do this, take the number of ohms you need divided the "Ohms per 1000 ft." rating on the chart. Multiply this by 1000 and that's how many feet you need. For example, if you need 6 ohms of 24 AWG wire, you divide 6 ohms by 25 ohms per thousand feet, and you get 0.24. Multiply that by 1000 ft and you should find you would need 240 feet of wire. If you don't know what gauge wire you have, like I didn't, you unfortunately just have to kind of play with it. Theoretically, you should be able to measure the resistance of, let's say, a 10 ft piece of wire, and divide the resistance you need by that. You would then multiply by the 10 ft to find the length of the wire. In practice, however, I've found that this somehow doesn't always work out how it should. Perhaps I didn't have a good connection to the wire when I measured it. Regardless, you can try this, and maybe mark it at the point you think it should be cut, but cut it a little long just in case then measure it. If it's too high, cut it a little shorter until it's on target.
Now that that's over with, you'll want to wind the wire into a coil. At this point, I would hope you have a cylindrical magnet picked out. The coil needs to be slightly larger than the magnet. I would suggest giving the magnet about a 1/4 inch of space all around it between that and the coil. If you have doubt that the two will be able to shake up and down without rubbing into each other, play it safe and give it a little more room. Once you decide how much room you want the coil to have around the magnet, you have two options. I usually find a glass that has about the same diameter as the coil I want, tape one end of the wire to an end of the glass, tie the other to a tree or a chair leg, and start wrapping it around the cup, then carefully pull it off and tape it into it's shape before it unravels. If you don't have a battery, or a cup, or something of the sort of a suitable size, you could wrap paper around the magnet until you have enough thickness to give your coil the room you want after it's done, and use that instead. Once you finish wrapping it, carefully pull the coil off and tape it so it keeps it shape. Be careful not to bend it out of it's circular shape at all. I usually wrap the two wire ends around it a couple times to hold things together better. Leave at least 3 feet of wire from each end of the coil to be plugged into the amplifier later on. You could plug it in directly or solder it to a thicker wire that won't break when it's hooked up to the amp and secure the solder joint inside the box so it won't rip apart. Obviously, you should electrical tape all the exposed wire or use shrink tubing. To solder magnet wire, or just to connect it to an amplifier, either use a lighter to burn off the insulation on the end of the wire, or sand paper to sand it off until it changes color. If you do use a lighter, you still may want to use sand paper to sand off the dark residue from the lighter. It comes off easily. You can get a rough idea of what the coil should look like from the picture in the next step. On to the box!
Step 2: Coil and Plate
Because the coil can get hot, avoid using hot glue for gluing the coil, and use a paper plate. Yes, I know the picture is a styrofoam plate. I originally used styrofoam and it did not work well. Superglue is the best glue for this because it holds very well and holds up well to heat. Superglue does dissolve styofoam plates, yet another reason to use a paper one. Measure the plate to find the middle, turn it 90 degrees, and you should have the center of the plate. Try to center your coil over this point as close as you can. Next, superglue it down. Take your time gluing. If the coil isn't glued well enough to the plate, you'll find the speaker rattles a lot. Glue it down tight. If the superglue is taking a long time to dry, use a blow dryer on low to speed up the drying. Once it's completely dry, flip the plate over. The magnet needs to fit inside the coil, so the plate inside the coil is now going to have to be cut out. Take a utility knife and carefully cut out all the plate inside the coil. Be careful not to scratch the thin insulative coating on the magnet wire! Make sure the magnet can fit easily inside the hole with a little bit of wiggle room. Once again, I would suggest about an 1/8 of an inch on each side. If the magnet winds up rubbing against the wire for too long it could short and either kill your amplifier or melt the wire. Next, center the plate on the side of the box you want the front of the speaker to be on. Hold or tape the plate down and trace around it. Remove the plate and use the utility knife to cut out a hole a little smaller than the circle you traced. You want the plate to have a bit of a lip to sit on, but it also needs to be able to move freely. Once you have the hole cut, set the plate inside the hole and check to see if it can be pushed in and out with a bit of bounce much like a normal speaker. If not, consider cutting the hole slightly larger until it can. Tape the plate down for now, but don't glue it yet.
Step 3: Popsicle Stick Scaffolding!
So far, we should have a coil of wire on a plate on a box with a hole in the middle of it all. Next, we need to get the magnet to stay centered perfectly inside the coil. You could do this a lot of ways, but I chose to make scaffolding out of popsickle sticks and hot glue to hold it in place. You obviously have a lot of freedom to use your creativity in engineering here. I show a picture of how I build mine as an example. You ultimately just want to hold the magnet perfectly centered inside the coil, so it should be strong. I find the most effective position for the magnet is to have the top of the magnet level with the coil. This is where the magnetic field is the strongest. Once you have it in place, glue it all with a generous amount of glue and stress test it a bit to make sure it won't fall out later on. Once again if it moves later on and winds up rubbing the insulation off of the wires, it's going to sound terrible probably short eventually. your speaker should be looking almost like a speaker, well as much as one made from a cardboard box and a paper plate can, that is. Now that the magnet is held in place, flip it back over so the plate side is up. Take off all the tape holding the plate on to the box. Put the plate in position and adjust it so the magnet is perfectly centered inside the hole. This is the last chance to make fine adjustments, so do it carefully. Once it's in place, put a dab of hot glue to hold one side down, still making sure it's adjusted properly, glue the opposite side of the plate so it can't move. Now you can glue all around the plate so it's air tight. As with gluing the coil, you're going to want to glue it down well to avoid rattling.
Step 4: The Final Stretch
In all technicality, you now have a functioning speaker. The only thing left is add a dust cap. In normal speakers, it keeps dust out which is important because professional speakers have the coil and magnet very very close together, so close that a small amount of dust would cause friction. In ours, dust is not as much of a problem as air escaping. The dust cap should help make it a bit louder and should hold the plate a little sturdier so it may sound a little better too. For mine, I cut the bottom off of a quart sized container I had from Chinese food. You should be able to find something that works equally well or better. Anything too heavy will hinder the speaker's movement, and anything iron will be attracted to the magnet and will do the same. The dust cap doesn't need to be too tall, just tall enough that the magnet can protrude past the plate a bit without touching it. Once you have a good dust cap, put it over the hole and glue it in place securely with hot glue. Voila! You've made a speaker almost entirely from old junk! And it should sound decent! They probably won't be able to handle as much power as decent normal speakers, but in the case of mine, it certainly sounds a lot louder and bassier than my laptop, phone, and most desktop computer speakers. You could of course paint it, but I chose not to to make it easier to show in the different components in pictures. My apologies for being rather long winded, but I hope I gave all the information you should need to build your own speaker from scratch.
If you thought this project was competition worthy, I'd appreciate your votes in the Tech contest. Just click the little "vote" ribbon at the top right. ;)
I'd be glad to help if you have any questions and would love some suggestions, Happy making!
Step 5: A Little More...
My speaker is of such quality that I use it to listen to music with while cooking. My only gripe was that with too much bass it rattled. Beyond that, it sounded very bassy and clean. I decided to see what was causing the rattling and ultimately fixed most of it. I shook the box around and found there were a few little dots of hot glue rattling around inside. I poked a small hole in the corner and got those out which helped. The other problem was the top and bottom of the box. Since mine was a wine box, there are thin, long holes on the top and bottom of the box which turned out to be largely responsible. I didn't want to glue the top one shut completely because an air tight speaker requires more power to operate, so I wound up putting a few supporting globs of hot glue across it to minimize shaking while still allowing airflow. I completely sealed the bottom hole. EDIT: [Airtight speakers, although higher in power consumption, tend to sound better, so I ultimately decided to make it airtight. It sounds a decent bit better, yet not much quieter.] Yet another cause I found was the box ratting on my counter top, presumably from small beads of glue that were touching it through the hole I patched. To solve this, I made legs with 3 dots of hot glue. I put two in the front and one large one in the back middle to avoid it being unbalanced like a chair with a short leg. This helped with the box shaking off of my counter top, but I found the legs I made still shake against my counter top making some noise. If anyone has a solution to this, I'd appreciate it. At this point, if I hold it in the air so the legs can't touch my counter, it has almost no shaking even at the highest volume my stereo can output. The last issue with the speaker is not shaking, but heat dissipation. Since this is not made with machine quality precision, there happens to be more resistance than induction working which means a great deal of the power is transferred into heat from the coil rather than sound. What I've found is that if I have it turned all the way up (it's not a very powerful amplifier) for any length of time, I start smelling the burning sensation of superglue being heated too much. This alone doesn't worry me as much as the coil heating to the point of burning the insulation off the wires. A solution to this might be to have a more cylindrical coil rather than a ring to provide more surface area for cooling. I've also made very thick coils with heavier gauge wire to handle more power, but they turn out so heavy, I think it would prohibit the plate's movement more than it would help. I'll probably also replace the dust cap with something smaller and lighter when I find something suitable. I don't want to use a waterbottle out of fear of it being too flimsy and noisy.