Any one up for a discussion?

[Miksoko]

I'm in the mood for a good engineering-based discussion. By engineering, I mean math, physics, programming, or whatever.
topics similar to:
refraction of light: why did it start, and was it first noticed in water or glass?
waves and electronics: why do microphones work, and who figured that out?
etc.

[plnyyanks]

Here's a microphone fun fact tied to a bit of music history. Microphones basically work in the same fashion as a loudspeaker, only in reverse (sound wave -> electrical signal and visa versa). It uses electromagnetic induction - sound waves move a magnet surrounded by a coil, producing a current.

But anyway, when recording Paperback Writer, Geoff Emerick (the Beatles' recording engineer) actually used a loudspeaker wired in reverse instead of a microphone to record the low end of Paul's bass better. That's why that song has such a distinct bass line. Fun fact of the day!

[Miksoko]

Correct! which, by the way, I think is pretty darn cool. How do you think someone discovered that?

[PAR_WIG1350]

If I had to guess, It started with two separate discoveries. First, the discovery that a moving diaphragm could pick up and reproduce sounds (ears and drums are respective examples that are respectively naturally occurring and well known throughout history). The second was that a current traveling through a coil can move things. Anybody passing a current through a long wire that had been coiled to keep it organized could have discovered this if there was any iron or magnetic material around, a compass would work too. Then the two were put together and the transducer was born.

[DonRotolo]

Originally Posted by PAR_WIG1350

First, the discovery that a moving diaphragm could pick up and reproduce sounds (ears and drums are respective examples that are respectively naturally occurring and well known throughout history). The second was that a current traveling through a coil can move things.

The first was a Thomas Edison thing - a cone with a diaphragm at the smaller end, the center of which was mounted a needle. As a wax-coated cylinder spun beneath the needle, screaming into the cone transferred the vibrations to the wax. Shellac the wax to harden it, and use the same needle-diaphragm-cone assembly to trace the wax impression, and sound comes out. But only once - the cylinder was ruined by playing it :-(

Of course, that system was eventually optimized a lot. Tinfoil coating, for example.

The second was a Michael Faraday thing, IIRC, but of course it wasn't seriously implemented in practice until amplification came about. But before then* Alexander Graham Bell used a bunch of carbon granules beneath the diaphragm which, when mechanically excited** generated a small current and, conversely, vibrated when electrically excited.

* Emile Berliner actually had the first microphone, the "loose contact microphone", but it wasn't as practical as the carbon granule type, which is still in use today.
**meaning 'have energy put in'. Don't get excited.

[Ether]

Originally Posted by plnyyanks

sound waves move a magnet surrounded by a coil, producing a current.

Typically, sound waves move the coil. The magnet is stationary.

By the way, the fact that these two cases had separate physical interpretations was a burr under Einstein's saddle that was a motivating factor for his 1905 paper On The Electrodynamics of Moving Bodies.

Microphones can also use capacitance (sound waves move a diaphragm which changes its capacitive coupling to a second diaphragm) and the piezoelectric effect (sound waves distort a crystal which creates a voltage).