Laterally Driven Speakers




About: Recently finished a Ph.D. in Mechanical Engineering. Still love creating in my spare time
This Instructable will teach you how to create a set of speakers. But, these speakers don't create sound by forcing an electromagnet up and down, they use electromagnets to vibrate permanent magnets side to side, laterally.

Step 1: Materials

What you will need:
- Scrap Wood or another material for a base
- Electromagnets, I pulled the ones you see from a broken CD drive
- Magnets, the smaller round magnets are pulled from magnetic ball and stick toys from the dollar store, and the two larger ones from a CD drive
- Plastic, such as from many electronics packaging
- Cardboard, such as from a cereal box
- Amplifier

Step 2: Prepare the Base

The first step is to cut four grooves as shown in the picture. The purpose of these is to hold the plastic rectangles under pressure, so the vibrations better resonate in the plastic.

You will want to make the cuts about 3mm deep and about 7-8 cm apart for each speaker. This is just enough for the plastic edges to catch hold.

Step 3: Add the Plastic Sheets

Cut the plastic rectangles about 8.5cm long and the width of the groove in the base. Just in case, cut too much so when you fine tune it you can cut the extra off.

The plastic is cut longer then the grooves are apart so it bows up about 1.5 cm in the middle, where the electromagnet will sit.

To get the sheets to stay in place, use pliers to bend a lip downward on each end of the rectangle, about the depth of the groove in the base.

Step 4: Add the Electromagnets

For this step all you need to do is tape the electromagnets to the base, so that they won't interfere with the plastic moving. Also so the side of the coil is in the middle of the speaker. Why will be explained later.

Step 5: Add the Magnets

To add the magnets, simply take one smaller magnet ind place it in the center of a plastic sheet from earlier.
Next you will need to add a stack of smaller magnets under the sheet so they are held in place by the magnet above the sheet. Be sure to add the largest magnet on the bottom of the stack.
The size of the stack will depend on your speaker, the point is to get the larger magnet close to the electromagnet without touching it.

Next place the ends on the plastic sheet in the corresponding grooves in the speaker base, as shown in the picture.

Step 6: Fasten Everything in Place

Take strips off the cardboard about the depth of your groove. The purpose of these is to buffer the plastic from buzzing on the base.
Take the strips and push them into the grooves alongside the plastic. Once you have it in place, tape the end down so nothing will move. Be sure to leave extra tape to be trimmed off later.
You will want to put some tape over the edge of the speaker to reinforce it, as seen in the pictures below.

Step 7: Power It!

The final step, add the amplifier to the speakers.
For my amplifier I used an H-bridge motor driver, good to 1A at 36 V.
For my music source I used an Atmega168 using PWM to generate sound.

There are many good instructions on the internet on how to build amplifiers, so I won't bore you with more details.

Step 8: The Physics (aka. the Fun Part )

These speakers work by the magnet being forced side to side, rather then up and down. This is done by placing the magnet over the wire itself instead of over the center. So when an electric field is generated, and comes in or out of the center of the coil, it loops around the outside of the coil and the magnetic field of the permanent magnet is either repelled or attracted side to side by the electromagnet. This causes the magnets to move and the plastic flex, creating sound!



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    41 Discussions


    7 years ago on Introduction

    Did you have to make a custom circute board? because that would be more practical that to hook up a computer to it plus it'd be SWEET to make a curcuit board output that electrical pattern.


    9 years ago on Introduction

     Built one of these using a 2x1x1 inch rare earth magnet, a big spool of wire as the electromagnet and a quarter inch thick sheet of plastic. The thing was 2x1.4 feet in size. Lets just say I expected more out of this behemoth. It created pretty good bass, but I think the thick plastic is my problem, need to go thinner. 


    9 years ago on Step 8

     truly innovative and inspiring model


    9 years ago on Step 7

    How do you scale this up for use with a surround sound system?


    10 years ago on Introduction

    good place to get an amp is to go buy one of those $10 mp3 player amps from a cheap shop. that should work, usually about 1.5w you could rip the speakers apart in them too for the coils. the magnets in a laser assembly in the cd player will work very well. seeing as your ripping apart a cd player anyway. i suggest you go buy a crappy second hand pc cd drive for cheap. anything more is just to nice a thing to destroy just for the magnets i think


    11 years ago on Introduction

    really cool project. I just built it and spent hours playing around with it. I didn't have that small magnets so I used hard drive magnets, which were a bit heavy and definitely made it more inefficient. Also I realized it's better to suspend the plastic directly above the electromagnet (actually works best if you hold it tightly against the electromagnet, but that takes a good deal of pressure). Also I think the CDrom or hard drive electromagnets are very inefficient for this purpose, as to get a volume where I could hear the song properly, I had to turn both the Ipod (aux input) and the amp the speaker was connected to to full power. It draws like 7-8 watts that way (18-20V 500-600mA), and the coil gets very hot (like hot enough to burn if you were to hold your finger against it.

    cool, i wanna make one! so the big electro magnets are from a cd drive, such as that from a computer right? and is it possible to simply twist the wires of the electromagnets onto the wires of an old pair of headphones, so that i can put my ipod on through these speakers? or does it have to be done differently? cheers! (and really cool instructable btw)

    5 replies

    To address you question about source hook-up, it needs to be run through an amplifier first, because a 1/8" audio jack doesn’t have enough power. For you question about electromagnets, I am pretty sure I got them from an old broken SCSI CD drive I had from 1993, but it could have also been an old 5-1/4" floppy drive. I also got the slightly larger permanent magnets from the laser assembly of a CD drive. Hope this helps :)


    Reply 11 years ago on Introduction

    They are probably from the floppy drive. I remember seeing the same kind of electromagnets in the magbot pendulum in Junkbots, Bugbots, and Bots on Wheels.


    thanks for the speedy reply; i should have an old floppy disc drive somewhere, so i'll have a look in there. i'll also open up the cd drive again to try and find the permanent magnets. thanks again

    i took apart an old cd drive, but i couldnt find any electromagnets! at least nothing that looked like your pictures. any guidance would be great. thanks!


    12 years ago on Introduction

    Very cool! A company called magneplaner makesscreen (as in room divider) speakers (or used to 25 years ago. Imagine a sheet of plastic about 5 feet long an 3 feet wide, with copper wire zzig-zagging about 1/2" apart across its surface. Behind that are strips of those rubber magnets that they use for refrigerator magnets, the strips located beneath the copper wire. Now run current through the wire. Voila! The whole 3x5 panel is a speaker! You can get really close to them and your ears won't hurt because the sound is distributed over such a large area, but they can be very loud at the same time. Excellent project!

    4 replies

    Reply 11 years ago on Introduction

    thanks, looks like i made a typo. could've sworn i checked it after i posted the link though, maybe they moved. regardless, thanks for fixing it.


    12 years ago

    This is really cool. I'm guessing you can't mount this thing sideways, though, right?

    2 replies

    Reply 12 years ago

    It doesn't matter which way you mount it, everything is held in place. It will work so long as the magnets and plastic are free to vibrate.