4 ms·
Keep in mind the black out wouldn't rule out any electric device that had batteries or capacitors as part of it. I had a smoke detector that made a slight humm
by genericuser 11y ago
Keep in mind the black out wouldn't rule out any electric device that had batteries or capacitors as part of it. I had a smoke detector that made a slight humming, took me forever to figure out where it was coming from, and replace that smoke detector.
- na85 11y agoBattery-powered smoke detectors will likely be running on DC so coil hum seems unlikely.
- bronson 11y agoUnless it has a switching converter or regulator. Even when running at high frequencies they'll often generate harmonics in the audible range. It can take a heck of a lot of effort to keep a circuit quiet and nonmicrophonic.
- dghughes 11y agoSuch as land line phones which still have power even in a blackout it's separate from power lines. The phone line power must be AC I can't see such long runs being DC.
- YupItsAUsername 11y agoActually, it's 48 volts DC (http://en.wikibooks.org/wiki/Communication_Systems/Telephone_System#Line_Cards http://en.wikibooks.org/wiki/Communication_Systems/Telephone...). A few years ago I got to tour a central office for a small telephone/cable company in a suburb of Houston and the phone lines were actually powered directly by massive banks of lead-acid batteries which were then constantly kept floating by the mains supply.
- reitanqild 11y agoAlso there is radio waves interacting with passive objects. I have been working with radio for the last few years and while my theory isn't that strong a colleague of mine was pretty clear that AM signals from planes (or control towers) had been observed to make detectable sound levels in nearby houses.