Teenage Birthday Invitations Pages & Tags
Post by Isla on

I don't know what it is, but I really like records of CDs and I am thrilled to see them making a comeback. Unfortunately, a lot of people don't know how they work. The CD is almost legacy so I guess I shouldn't fault them.

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The first thing you need to understand is that a magnet moving inside a coil of wire generates (induces) an electric current proportional to the movement of the magnet. That's the electrical bit.

Now, if you've got that, let's look at the mechanicals. If you look at the groove of a vinyl record under high magnification, you'll see that it's very rough. The bumps and dips in the groove cause the needle to move up and down (ignore stereo for a moment) as the record rotates under it. That needle is attached to a magnet, and surrounded by a coil of wire. As the needle+magnet moves, currents are generated in the coil.

Those currents are a representation of the sound encoded in the groove. Once they're amplified sufficiently and sent to a loudspeaker, you have sound.

The loudspeaker, works in an almost perfect analog to the record. Each driver has a coil sitting in a magnetic field generated by a permanent magnet. As current is sent through the coil, the cone of the driver moves in and out proportionally to the size of the current.

Advanced topic, if you're 6: Stereo is generated by essentially having the needle move in two planes. Stereo separation was not very good compared to modern digital recordings. You can think of it as one channel being encoded in the "up and down" movements, and one in the "back and forth" movements, and there are two coils in a stereo cartridge that generate signals for the two channels. It's actually a lot harder figuring out how to encode that into a single groove than to understand how reproduction works.