Home » Uncategorized » The Work of Alec Salt (technical)

The Work of Alec Salt (technical)

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

If you’re up for it, Salt takes you right through the anatomy of the ear, weighting scales, and infrasound as they relate to wind turbines in this terrific article. NOTE: I am linking you to the original document (with 2014 update)  from the authors themselves (the published article had typos). I keep coming back to this article for the basics, as well as for the cutting edge. Reading and understanding this article on a good level is equivalent to a college course, I’m sure.



  1. Jonn N says:

    Have you tried mapping the reports out? Make a line out and of them it could be maglev tunnels being dug deep underground in straight “ish” lines to strategic locations throughout the world. Just a thought.

  2. The Salt/Lichtenhan (S/L) paper is quite interesting and offers good ideas possibly relevant to the Hum; the difference being that wind-turbine infrasound is almost certainly acoustic, while the Hum seems to not have an acoustic counterpart. The common ground is possibly the inner ear – particularly the Outer Hair Cells.

    S/L are quite correct that using “A-weighted” sound level measurements when discussing infrasound is completely absurd. It is equivalent to: Is X harmful? Assume X does not exist. X is not harmful. The A-curve assumes SINUSOIDS and essentially, the Fletcher-Munson equal loudness. It is a bias (bandpass filtering within the meter or program) of the input sound. It should relate solely to sound frequencies as perceived. It does not suggest that physical vibrations amplitudes are actually damped. By comparison, suppose we discover a square centimeter region on our hand that is relatively insensitive to touch (and to pain). Can we drill a hole there?

    [The A-curve, and the competing, better C-curve are, widely used in loudness measurements. Use of the A-curve for this is responsible for low total readings in cases where the party next door knocks you off your foundation with its misread bass thumps! Readers interested in a lightly technical description (written for legislators considering noise ordinances – but of course – never read!) might like my “Considerations for a Noise Ordinance” (2003) http://electronotes.netfirms.com/AN357.pdf ]

    An important discussion of S/L centers on their Fig. 2. There they show an Amplitude Modulation, and the modulation shows an approximate doubling of the signal FOLLOWING (delayed) the peaks of the low-frequency component (4.8 Hz). Note well that the peaks are the points (think derivative) where the low frequency component was just before minimally varying (temporarily quiet). Not unlike an AGC (Automatic Gain Control).

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