A month ago I bought a set of new computer speakers and strung them together with my existing speakers that I had moved to the kitchen, the idea being that I could then listen to music or the newsfeed while I was cooking or doing the dishes. I noticed that if I turned off the computer or unplugged the dual audio jack from the machine (like when I wanted to use a headset), the two speaker sets would set up some kind of resonance between them and start spraying out a really nasty humming sound. Didn't know what it was or how to fix it, so I just got in the habit of depowering the speakers whenever I turned off the computer or used the headset.
Since I got back from vacation, I've been working on a kind of techie section of this book I'm trying to write, that involved a lot of research into the very low end of the electromagnetic spectrum, and completely randomly blundered into what's causing the hum in my speakers. I was looking into some material about these people that track ELF submarine communications, and found that there was always a strong band of electromagnetic noise at 50 or 60Hz (European or American systems)... turns out it's just noise from the national power net, and it's the same phenomena that is foxing my speakers.
So when you hook two systems with internal grounds together, sometimes they create a "ground loop" and you get this nasty hum. I'd never have known if I hadn't been researching ELF just now, just this week. It feels like one of those moments of synchronicity, like back when I was living in San Francisco and for about a year--with a consistency that was scary after a while--the jukebox would start playing "Sympathy for the Devil" whenever I walked into a bar.
Anyway, the research and the writing are why I've been a terrible correspondent lately. I'll get back in the game soon but I have to do this now.
Posted by case at March 2, 2005 09:04 PM