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A Non-Technical Experiment Waiting to Happen

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The VLF radio theory can be tested this evening, without special materials or technology. VLF radio waves (between 3 kHz and 30 kHz) can penetrate earth to considerable depths, depending on the conductivity and magnetic permeability of the ground. Therefore, if one descends deeply enough underground, VLF signals are fully blocked, and this Hum hypothesis can be tested. There are passing references in a few Hum articles to people going deep into limestone caves, but not a lot of detail is available on those investigations.

The sharp reader might ask: wouldn’t this block sounds as well, so if the Hum is silenced deep underground, how do we know what the source is? It turns out that sounds can travel well through solid rock. This doesn’t perfectly sort out VLF radio from acoustic sources, but it helps.

From a quick scan of the VLF literature, it seems that VLF radio has a maximum earth penetration of no more than about 150 metres (about 500 feet). If a reader familiar with this literature has other information, by all means, pass it along. A few years ago I began discussions with the group that oversees a deactivated copper mine close to here, but I turned my attention elsewhere. It may be time to open those lines of communication again.

There are many places in North America and Europe where deep caves or deactivated mines are found, although access might be problematic (or illegal) in some cases. Also, if one of you does get permission, or the nerve, and get a guided tour to go underground, note that all mains electricity and other equipment need to be shut off. Running water of any kind will also skew the results. And please be careful.




  1. Two cautions:

    FIRST: safety. Isolating oneself, in a cave/mine, or in a Deming box is a serious matter. Always be sure you can take a step backward (literally, or like turning power back on), that you have a Plan B and a Plan C as backups, and that someone knows where you are and when to worry if you are not out. Simple but essential.

    SECOND: what are you trying to prove? Ostensibly, perhaps you suppose you are just trying to demonstrate that the Hum is not “heard” inside a cave, and thereafter inferring that the Hum is caused by VLF radio which was blocked by the rocks. Not even close! To begin with, is a POSITIVE finding the presence of the Hum, or the absence (presumed “blocking”) of the Hum? You could choose either, but you must choose one or the other – and choose BEFORE discussing the meaning of your evidence. And the analyses for the different cases are not symmetric.

    Suppose you have set up the experiment well and you hear (and tested) the Hum successfully outside the cave. You go inside and hear VIRTUALLY the same thing. THAT would be significant. You could conclude (with a follow-up confirmation of two), that either (A) the Hum is internal to yourself, or (B) that IF the source of the Hum is external, whatever it is (AF, RF, new-age vibrations!, etc.) the cave does not block entrance. This (hearing the Hum inside) is really the ONLY result for the experiment that would clearly mean anything.

    NOT hearing the Hum inside the cave, by itself, would mean nothing. The experiment needs to be controlled, and the result evaluated statistically. Most typically, people who claim underground blocking relate a one-time event, and do not even say if they successfully heard the Hum outside either first, or afterward. Even a contention that the Hum is NOT heard inside a cave (blocked, or perhaps just “masked”) would require that the Hum actually be heard outside and not subsequently inside on perhaps 6 or more consistent trials. (This is unlike the case of hearing the Hum inside where one or two instances would be rather convincing.) Unlike the supposed similar Deming box, one would suppose that the particular conditions inside a cave would be virtually impossible to evaluate (resonances, dripping water) let alone control.

    { As an aside, the control alternatives for a Deming box should probably be the same INSIDE. If the RF blocking box has heavy metal walls, probably the AF box should also have hard walls (like at least plywood), as should the control. The AF blocker should NOT be “anechoic” but rather acoustically insulated (the inside-out version of an anechoic chamber). }

    • I think it’s a test that’s accessible to the lay person, and we know that there are many hearers who are highly motivated to see what might block the Hum. It’s not designed to have the types of controls or pre-analysis you are suggesting. I’d be happy to hear anecdotal reports from people; if I hear a lot of consistency in what they experience before and after, that might provide impetus for more formal stuff.

      • Glen –

        The general experiment you propose (i.e., is the Hum heard underground?) is likely better served by 5 to 10 brief but good-quality controlled observations, by experienced Hum hearers, (along with carefully and completely written reports as primary evidence), rather than by 1000 untidy anecdotes subjected to statistical methods (which no one really understands anyway).

        I agree that the test is accessible to a lay person (with good observational and analytic skills). But some guidance on REPORTING in a useful way (even a checklist) might be both necessary and adequate.


    • Charlie says:

      On the other hand, evidence for the existence of the hum itself is based on thousands of anecdotal reports from a variety of people in a variety of situations. Individually these reports might not mean much, but as a whole they could be taken to suggest that something is happening, and that there might be common factors involved. Maybe in similar way, a mass of anecdotal evidence about going underground could also be seen as suggestive.

      I agree that there are lots of variables, and that the result could be interpreted in different ways. But if the hum is caused by VLF, then it seems reasonable to me that going deep underground could possibly have an effect on it. If an effect were noticed it may not prove anything, but it might suggest VLF as a possible culprit. And if no change is observed, then maybe that casts a shadow on the VLF hypothesis.

      It’s all a bit vague, I know, but at the moment we seem to be stuck with trying to make sense of clues and anecdotes (albeit lots of them). Hopefully experiments like Glen’s will help provide some harder evidence.

      Anyway, I would like to try going underground, just to satisfy my own curiosity if nothing else. I read about caving last night and it sounds dangerous and difficult, but there are a number of public caves and ‘show mines’ here. It’s just a matter of finding one that’s deep enough and reasonably nearby.


  2. Gerry says:

    Hi Glen, I posted a version of this a few days back to an earlier thread (‘Competing theories’) in reply to “Dan” who came up with a good experiment which seems to show a vibration of some sort emanating from the ground up.

    It’s the mention of limestone and caves in this new header that has triggered my ‘layman’s’ imagination into overdrive.

    Perhaps I’m wrong, but I think it might be worth further consideration?

    Re earlier post to Dan under header: “The competing theories”.

    (April 22nd 2016)

    Really interesting post and experiment Dan, which I’ve yet to try but intend to.

    (But I do not doubt you!)

    Your theory of vibration coming from the ground up and somehow causing us to perceive ‘the hum’ makes sense.

    I started perceiving the tone back in 2011 and at that time I firmly believed it was reverberating through the structure of my home and coming up from below.
    I imagined tunneling was taking place or similar(24/7!!) and the local councils had not informed us about it!
    This turned out to be partially true(they were adjusting a subterranean rivers flow in order to redirect it to stop local flooding above), however, the work was minimal and only happening during the standard 9 to 5 schedule.

    Nowadays, I ultimately have no idea what direction the perceived tone(the hum) is coming from,  as I’ve long since gotten lost in its complexities(and then some!).

    But, one of the ideas I’ve considered as a smoking gun(and I’ve had many of these!!) was the possibility that global ‘hydraulic fracturing'(aka Fracking) might just be a factor here??

    Some serious forces are being used here to dislodge gas(etc) out of deep rock formations from below.
    (And it’s a renowned controversial process too!)

    Could the forces be causing global traversing seismic ripples, microscopic in intensity, but somehow getting converted into a frequency as it comes up by way of resonating through buildings.
    Or it may be a frequency (created by the engineering process) from the ‘get go’ and it simply gets amplified by buildings or by our auditory senses or both???
    (Sounds mad, but there are geniuses out there who’ll no doubt be able to work this one out!!)

    I would hazard a ‘layman’s’ guess that it wouldn’t take too many of these things running simultaneously at different locations globally, to cause this! 

    So, an international ‘harmony’ of resonating buildings creating a frequency which is being perceived as a tone somewhere in our auditory senses caused by hydraulic fracturing might be causing the damn hum!!(phew—maybe I need to put a few commas in there!!!)

    Also, I wonder if there’s a correlation between high densities of sedimentary rock of a specific type(limestone being the most obvious!) where most fracking is taking place.

    Could this be a precursor to the creation of the specific resonance that in essence, is what we perceive as the Hum??

    Might be worth trying to tie up Glen’s hum map with known global fracking sites, to see just where and when these things are active.

    It’s got to be worth considering at least!



    Incidentally, Hydraulic Fracturing has been around since the late forties, so the timeline is concurrent to historic hum reporting.


  3. AC says:

    Having just discovered this website I am happy that others have validated my hearing the hum and are thinking about its source.
    I live in a rural/suburban area where there is no nearby fracking, and our limestone bedding plane is extremely thin. However, there is a quarry about seven miles away, a truck distribution center about a mile away, a number of farms within a two-mile radius, an interstate about two miles away, train tracks looping around the neighborhood as close as 3/4 mile at one point, and some new home construction within two miles. With all of that going on around me, I still only hear the hum periodically. I’ve always guessed that it is a generator at the truck distro center, a train locomotive sitting idle on the tracks, or a number of parked trucks whose idling engines begin to sound in sync.
    I do, however, go caving in my region where the limestone bedding plane is thick enough to have formed caves. I have never heard the hum while underground.
    While anecdotal, my experience over the past 10 years or so may add to the total picture. …

  4. Charlie says:

    Hi AC,

    I was interested to read about your caving experience re. the Hum. As I recall someone else here reported a similar effect (ie. that the Hum stopped when they went down a cave). But apart from that I haven’t found much concerning people’s Hum experiences underground.

    I’m not a caver, but there are public limestone caves here in Australia and I have often thought about making the trip to one of them and trying this experiment for myself. But it involves a lot of driving to get there, so thus far I haven’t done it. Your experience though has left me wondering if I shouldn’t reconsider making the effort.

    I do have one question: – how deep were you when you noticed that the Hum was gone?


    • Charlie –

      The suggestion of traveling; a “lot of driving”, (apparently long road-trips may disrupt Hum hearing); and of then going down in a mine (changing pressure in middle ear); and with a group (?), suggests a confounded experiment at best. Why not try to find someone already there who is used to going into mines (like a hearing miner) and see if he/she finds the Hum blocked, or not, inside. Or do mines run 24/7/365? I don’t know.


  5. Charlie says:

    I hadn’t thought about the effects of a long drive interfering with the experiment. On the other hand I have made a couple of long road trips in the last year, but I didn’t notice any effect on my perception of the hum.

    The possibility that air pressure could an effect is a good point. As you say the increase in pressure down a mine could be responsible for Hum disruption. Maybe it’s possible to find a mine or cave that extends horizontally into a hill or somesuch.

    Ambient noise from people and /or machinery is something I have thought about. It would depend a lot on the situation, all I can say is that i have learnt to detect the Hum in fairly noisy environments. For instance it’s raining heavily and noisily here atm. but I can still ‘hear’ the Hum through the racket. But even if it involved a popular tourist cave it might be possible to find a quiet time or spot.

    I don’t know of anyone I could send in my place. But AC has first hand experience and there was someone else who said something similar a while back as well. (I’ll try and dig up their post.)

    Anyway, I wasn’t actually planning to take off to a cave just yet! But reading about AC’s experiences reignited my interest in this line of investigation. It’d be interesting to hear more from them (AC) and or anyone else who has been down a cave/mine.


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