Source of Plymouth Hum Discovered?

There are a lot of places in the world where a certain percentage of residents report hearing a strange hum. There's the Taos Hum, the West Seattle Hum, the Windsor Hum, the Auckland Hum, the Kokomo Hum and the Bristol Hum to name but a few.

The Plymouth Hum as described by residents in The Plymouth Herald:

“You begin to wonder whether it’s you, your ears, but my husband said he could hear it too, and he doesn’t usually notice it.

“My neighbours have been aware of it too, several people say they have heard the same thing.“It’s a very low, almost melodic sort of sound.

“You wake up and thought it was something in the house. You can’t say it’s loud, but it’s a nuisance.

“We don’t hear it in the daytime, only at night.”

Daisy Rose said: “I hear it mostly at night when it’s quiet and I’m watching TV.“I have to keep pausing it because it’s so annoying. It does sound electrical in a way. Strange!”

Throughout the years many sources for these mysterious hums have been hypothesized from industrial machinery (Zug Island, Windsor Hum), fish (Midshipman fish, West Seattle Hum) and human physiology/psychology to secret naval programs and the more fringe speculation about HAARP and even UFOs.

Now a French researcher from the Centre National de la Recherche Scientifique is championing another possible source. (from Plymouth Herald article linked above):

Fabrice is convinced the water holds the answer. He has said it's down to the pressure of the waves on the seafloor that "generate seismic waves, which cause the Earth to oscillate."

Fabrice's theory is that continuous waves produce sounds that last up to 300 seconds at a time. The sound is picked up by people sensitive to low frequencies.

"We have made a big step in explaining this mysterious signal and where it is coming from and what is the mechanism," Fabrice said of the study, which was published in Geophysical Research Letters, a journal of the American Geophysical Union.

Fabrice Ardhuin's hypothesis was first reported on in April of this year when it was put forth as an explanation for the Bristol Hum following the publication of his study in Geophysical Research Letters. I couldn't find the paper available free of charge but more explanation is available in an April AGU blog post.

a reply to: theantediluvian
Do not discount machinery. I worked on a couple of high pressure pumps at a coal fired generating plant. When they were turned on no one could approach within 100 yards as, even with ear protectors it was extremely dangerous, the vibration would move you along the floor.
Now what I'm getting at was the generating plant was in a small valley yet villagers 5 or more miles away were experiencing low hums when the pumps were on. It took quite a while to find the culprit for the mysterious hum and when discovered I was one of a team that enclosed the pumps and stopped the hum.
So I say again, do not discount machinery even if it's far away.

a reply to: crayzeed

Agree. I believe many of the reports of noises come from fracking activities. The sound could propagate long distances depending on particular acoustic conditions at the time.

The GRL paper did not seem to give explanations for audible acoustic frequency (15-60 Hz) waves in atmosphere---it was on much slower waves not audible, but only visible to global seismographs.

I'm not convinced the Bristol paper particularly asked the author whether his theory explained the audible signals. The 'mysterious signals' described by the author were seismograph measurements, not hums.

Abstract

Microseismic activity, recorded everywhere on Earth, is largely due to ocean waves. Recent progress has clearly identified sources of microseisms in the most energetic band, with periods from 3 to 10 s. In contrast, the generation of longer-period microseisms has been strongly debated. Two mechanisms have been proposed to explain seismic wave generation: a primary mechanism, by which ocean waves propagating over bottom slopes generate seismic waves, and a secondary mechanism which relies on the nonlinear interaction of ocean waves. Here we show that the primary mechanism explains the average power, frequency distribution, and most of the variability in signals recorded by vertical seismometers, for seismic periods ranging from 13 to 300 s. The secondary mechanism only explains seismic motions with periods shorter than 13 s. Our results build on a quantitative numerical model that gives access to time-varying maps of seismic noise sources.

So they model waves with periods of 3 to 300 seconds. Even the shortest period is 1/3 Hz which is not audible.

a reply to: crayzeed

I wouldn't rule out machinery at all. My guess is that though there are similarities among the various reported hums, there's likely a few different sources. In particular, the West Seattle Hum which was originally blamed on midshipman fish seeking mates (and later ruled out) seems to have been tracked down and successfully suppressed and I remember watching something about the Windsor hum a year or two ago which seemed to conclusively link it to some industrial process on Zug Island.

That said, I think it's reasonable to say that natural processes generate more sound waves than anything else on the planet — from babbling brooks and crashing waves to whistling winds and the low rumble of thunder to the less common eathquake booms.

The strangest I've personally heard was the sizzling sound of meteors during a meteor shower. It's believed those are actually the result of RF waves emitted by meteors causing nearby objects to vibrate.

Hi, hum-no-fans !

Do the persons hearing the hum have electrical heating in the house ?
Is the frequency of the hum 50 or 60 cycles/second ?

I DO hear a very low volume hum from my radiators, when they are ON. . .
. . .just asking. . . B-)

Blue skies.

My sensitive ears pick up frequencies now and then. A lot of them that surprise me sound like television hum, like the old tube televisions. In fact, way back when everyone owned tube televisions, every time I turned that knob to the on position when the picture expanded like a rubber band an odd pitch-shifting sound would go through my ears.

Generators, transistors, anything with a strong enough electric charge, machines, devices, all that I at one time or another consciously noticed an audible signal. Sort of like monotone notes or hums as already described in this thread.

This seafloor explanation makes sense as all matter that moves creates a signal. That's a lot of matter (water molecules) on the ocean floor, being that it can emit an audible signal that some people can pick up on sounds plausible.

a reply to: mbkennel

The GRL paper did not seem to give explanations for audible acoustic frequency (15-60 Hz) waves in atmosphere---it was on much slower waves not audible, but only visible to global seismographs.

I'm not convinced the Bristol paper particularly asked the author whether his theory explained the audible signals. The 'mysterious signals' described by the author were seismograph measurements, not hums.

I understand what you're getting at from reading the abstract but if you read the supporting information PDF (which is free at least), you'll see that the authors do.

it seems to me that if continuous waves caused the earth to oscillate, and people with sensitive ears hear the low frequencies.
that there would be reports of people hearing the hum in history.
especially before the industrial age when there was no machinery, or vehicles or anything that would causes such noise.

a reply to: theantediluvian

Can you elaborate? I didn't see anything in there with a brief look.

a reply to: mbkennel

Stars for you!

I had a chance to read over the supporting information document again and it's not clear whether the paper addresses an acoustic signal that would be audible to humans. There are references to "the hum" but from the context it seems more likely they're referring to a "hum" as picked up by seismographs.

Interestingly though, in regards to the Bristol Hum, this paper was originally reported on by a number of news sources (including Wire UK, Independent UK and News.com.au) which all make the same claim as the Bristol Post article but it may be a bit of mutually beneficial sensationialization.

I'd like to read the paper to see if there's mention of an audible hum and some hypothesis for explaining how it could emerge from the microseisms — but not enough to buy it.