Magnets. They're pretty cool. If you connect a magnet to some thin cone, and run just the right currents through a wire somewhere in the mix, you can even get them to make weird noises. And that's what we call a speaker! But, for an class of Physics C students, that's probably fairly common knowledge, right? After all, I'm sure we've all seen the speaker contraption floating somewhere around the room. But wait - there's more!
As a matter of fact, some speakers and headphones (and microphones for that matter) don't actually use magnets to make their funny sounds! "What?! How can you make something move with electricity without magnets?", you may ask. Well, I'll answer your question with a question: do you remember that whole unit we did about charges that don't move? The whole one that makes your hair stand up and lets you shock your little sibling when you're wearing slippers? Well, that's just about all you need to know, really. It's only a few steps:
- Take a stupidly thin film of something flexible, and make it nice and charged
- Place that thin sheet between two more thin, conducting sheets
- Use your audio signal to change the voltage between the two sheets
- Bam! The thin film moves with the sick beat from your mixtape!
"But wait a second, I can't hear a thing! What gives?" Well, things get a bit complicated with that third step. You see, headphones have a little number called impedance attached to them. For the simplicity of this post, and so I don't have to actually do extensive research into it myself, we'll just say that higher impedance speakers/headphones are more difficult to adequately provide clean, powerful audio signals to than lower impedance ones. So anyway. Those little white earbuds you have in your pocket? Those probably have an impedance around 50 Ohms, depending on which brand they are, etc. Headphones driven by the method given above? Those have an impedance upwards of 150000 Ohms! That's quite a bit higher! So, in order to properly use these headphones and speakers, you'll also need to get a hold of a really powerful amplifier. Then, you'll be able to hear the sweet sound of electrons being lazy and not liking one-another.
So, that's about it. Magnets: they're pretty cool, but they're not the only cool kid in town.