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Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
This has been puzzling me for years. If I listen at anything that's connected to mains here and it emits buzz (such as a transformer), there's a weird rattling noise added to the hum at a pattern. It usually goes for 1sec. then goes away for 2secs. There are several second breaks where the weird sound goes away.
I'm attaching a sample of the sound that I've recorded near a running transformer.
Anyone dare to guess what it is?
(ignore the "chirping" sound it's a recording error) ]1199377664_152_FT0_strangemainshum.mp3[/file]
Registered Member #914
Joined: Fri Jul 20 2007, 06:22PM
Location: South Bend, IN
Posts: 85
Hook an oscilloscope up to it (using series resistors or an isolation transformer) and take a look. It may be a broadcast digital control/timing signal of some kind.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
EastVoltResearch wrote ...
Thats the core vibrating.
Really? It will go 1 sec on 2 sec off then go away for several seconds, the pattern repeats. Sometimes it gets a bit irregular but not too much. I believe I heard other things than transformers to emit the same pattern but I don't want to make false claims.
I'll try to scope it and see if I can see anything :p
... not Russel! Registered Member #1
Joined: Thu Jan 26 2006, 12:18AM
Location: Tempe, Arizona
Posts: 1052
It's difficult to say what exactly is going on, because the mp3 compression damages the waveform, but at first glance, it appears to be very regular, which is quite interesting. It looks like modulation of the mains, but it's hard to say if that is an artifact of the mp3. One thing that would be helpful would be to get a longer .wav file of the sound the transformer is making, as clear as possible.
Really really helpful would be to construct an isolation transformer, an attenuator, and put the results directly into your soundcard, then get a .wav file of that. That would obviously require extreme caution, however.
At any rate, here is what I got by running it through a narrow filter -- quite obviously a pulsed signal, suggestive of a timing signal of some sort. ]1199390100_1_FT36858_strangehumprocessed.mp3[/
file]
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
HFsstc-freak wrote ...
A friend of mine in cz have identified the buzz, its HDO, 216.6Hz for turning water boiling on and off.
Hmm, but why it has such complex pattern then? If you listen to the 7min file I posted, you'll notice there's an over minute long pattern which seems to repeat and is a bit different every time.
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Strange mains waveform/"rattling" noise
