Something we’ve wanted to print ever since we built the first Argentum is a speaker. I know what you’re thinking, thats like… a 3D thing, not a 2D circuit. Well, continue reading to find out how we made it!
Most readers of this blog will have a some idea of how a speaker works, but if you don’t, or even if you do here’s a whimsical quick recap of 20th century physics and to a lesser extent biology. If you already an expert in acoustics, please continue when you see the word HERE.
If I set off a small explosion, a large amount of gas will be produced in a small area. The large mass of gas doesn’t want to be in the small area and will start to expand quickly. As it expands it will change the pressure of the air around it. When the increase in air pressure gets to ear, it forces your ear drum to move inwards (just a little bit) and your brain recognises this movement as sound. This is because the pressure on the outside of your ear drum is greater than the pressure on the inside. Sound is just changes in air pressure.
At the location of the explosion the air is trying to get away so quickly that eventually too much air leaves, and a vacuum is formed because not enough air is left. This in-turn causes the air that was moving outwards to rush back inwards. Air pressure wants to be the same, everywhere in an open space, but it takes a while for gas to travel. This process of under and over pressure repeats over and over again, very quickly and eventually is damped out because of friction in the air. If you plotted pressure vs. time at a particular point in space near an explosion this is what it would look like:
At this point you might be thinking, this this is all well and good… but we’re talking about speakers, not explosions. Is a speaker just a bunch of tiny explosions? How many beans make five?
A speaker is just a surface that vibrates. As it vibrates it moves forward, and backwards, and then forwards again, and then backwards again. Forwards creates a positive pressure, backwards creates a vacuum. Just like in a explosion these changes in air pressure move outwards from the speaker and eventually get to your ear. The type of sound you hear is just the frequency, or number of times per second the pressure increases then decreases.
The surface is moved backwards and forwards because it’s pushed and pulled by an electromagnet. In most speakers the electromagnet is made from a coil of wire wrapped around a cylindrical magnet. An alternating current is passed through the electromagnet which causes a force to be exerted on the magnet. As the current is alternated it’s pushed and pulled, each time moving the surface forward and backwards.
So turns out you can’t explain how a speaker works without a bunch of prerequisite knowledge, but now that we’re all up to speed lets talk about how we printed one!
There’s no reason that the coil of wire needs to be wrapped around a cylindrical magnet. It is better because you can get more wire closer to more magnet, and produce more force on your surface but there’s no reason you couldn’t have a two dimensional speaker and put a magnet behind it.
It sounds insane right. Just printing a coil on a surface, put magnet behind it and enjoy some smooth jazz. We didn’t think it would work but it was that simple. So far we’ve tried it on paper and Polyamide but it should work on any flexible surface.
To power the speaker we just cut up a 3.5mm headphone extension cable and plugged one end into a radio. At first we didn’t think it was working but after we remembered to put the magnet behind, spookily sound started coming from the paper.
We can print a speaker on pretty much any flexible material. Here’s a video of the speaker printed on paper!
Want to see a speaker printed on something else? Leave us a comment and let us know!