US, California · 2018-05-15 · from the WORLDHUMMAP archive
A low hum in US, California
Very low frequency rumbling, like an engine idling at a distance I put together a simple experiment: connected microphone to PC and downloaded some free spectrum analyzer software. In range 0-100Hz, it shows single large pick at about 20.5 Hz, which is one of Schumann resonance frequencies. It makes me to believe Schumann resonance is the root cause of the hum.
Probably not every microphone can pickup such a low frequency, I'm using Yamaha YPAO Calibration Microphone, which came with Yamaha A/V receiver, and it worked.
What they reported
First noticed: 1998
Pitch: 20Hz
Loudest: During the night
Where: Equal indoors and outdoors
Symptoms: Insomnia;Sense of vibration;Anxiety
Changes with weather: It does, but I'm not sure how
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This is a Hum report from Dr Glen MacPherson's World Hum Map, an open, worldwide record of people who hear an unexplained low-frequency hum. Reproduced with permission and with thanks; the project is at thehum.info. We remove anything on request. Location shown is approximate.
Anomaly