Home » Uncategorized » Just before I go off the grid for a few weeks…

Just before I go off the grid for a few weeks…

Follow World Hum Map and Database Project on WordPress.com
Follow World Hum Map and Database Project on WordPress.com

Apart from a BBC interview on July 20th, I’m going off the grid for a few weeks in central Canada. When I get back and begin sorting through dozens of emails, it would be great if somebody will have sourced out for me two, highly sensitive low frequency/infrasound microphones to do beamforming with my Zoom H4n Pro recorder. I know less about this side of the research, but I am rapidly learning and need technical advice.

For those of you who know this field well, would this be a cheap option? http://volcanomodels.sr.unh.edu/jbj/MICROPHONES/J1%20Basic.pdf


  1. Ian says:

    Hi Glen,

    BBC interview? Please could you elaborate?

  2. David says:

    I give a call out on Facebook.

  3. Chris McPherson says:

    This filter circuit will pass 0.1 to 12 Hz but the slope past each break point will be a single pole (ie 6db/octave or 20 dB/decade)….. Wile this might be steep enough to make your measurement I would be interested to find out if a steeper slope would be better.
    I believe that what you are trying to do is filter out un-wanted signals…the question is then is how much of the unwanted signal can you put up with.
    In this example if 12 Hz is the corner of the upper side of the filter by the time you get one decade away or 120 Hz the interfering signals recorded would be attenuated by approximately 26dB (-6 + 20). This may be enough but I would be interested in understanding “beamforming” better to discover if in fact a single pole filter is sufficient.

    • Chris-

      Here is the math and a plot for the frequency response for the microphone filters. This is an EXACT calculation.


      The filter is “not bad” for a passive cascade. I suspect Glen wants to raise the LP cutoff. I have explained to him in an email how to do this. I am finishing up an app note on this whole thing – neater than my handwriting! It will be AN429.pdf. Same link as draft above – up in a couple of days. Works much better than I would have guessed.


  4. Heinz Schneider says:

    can you please explain, what you want to do with the microphones and the Zoom Device.
    I thougth, that audio beamforming does mean a technique to localize the source of an audio signal getting additional informations through collecting travel times by several microphones (time-to-run analysis)

    • I aim to first use a very sensitive and high quality microphone to see if the Hum can be captured. If it can, I intend to use beamforming to try to locate its source. If I had $100,000 and industry experts, this would be a snap. Alas, I have only hundreds of dollars and the kind assistance of several dedicated people who are following this project.

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