What Is Infrasound?


I inserted the assembly in a glass jar, plugged it with styrofoam and mounted the affair outside under a clay flower pot with a rock on high. The rock is positioned so as to not utterly block the drain gap. I’ve additionally added delivery peanuts to the jar to kill its resonance. This preamplifier offers about 20 dB acquire (x 10) and “bass enhance” below 10 Hz right down to 1 Hz. I used again-to-back capacitors on the output to avoid polarity problems.

Note that although the sensitivity is rolled off, alerts may be seen all the way down to a couple of Hz in locations. Ignore the 60 Hz line but right under it is another frequency produced by the mystery engine. No helicopters but; they have the same backwards integral signal look but centered extra close to 20 Hz. The ubiquitous electret microphone typically has a flat frequency response to below 10 hertz with usable sensitivity to simply a few hertz.

It seems that the background noise increases sharply at the low frequency finish of the spectrum, quicker than the response of the microphone rolls off. Here’s a spectrum plot displaying the microphone response with and with out that breather gap coated with tape. The sensitivity of this microphone is sort of excessive, absurdly excessive really.

The air inside the microphone case must be absolutely still. The following circuit uses a single CD4049UB to generate sine, sq., and triangle waveforms all the way down to very low frequencies (.03 Hz or even lower if desired). A unique wave shaping circuit give harmonics as low as -40 dBc even at 30 millihertz with out long begin-up wait instances.

Just connect either both optimistic or both adverse leads of the capacitors collectively. Those might be larger values, perhaps 220 uF, to avoid low-frequency roll-off if the sound card has a decrease than common enter impedance or if the tip and ring are related for some purpose. For example, here is a big picture from this morning utilizing this microphone. Note the engine starting round 44 Hz with harmonics (and probably subs, too). There’s a couple of passing aircraft and a weird trace up close to the highest.

Further work at the zoo with William Langbauer Jr. and Elizabeth Thomas revealed that elephants had been indeed making infrasonic calls . This was later confirmed with playback experiments on wild African elephants in collaboration with Russel Charif, Lisa Rapaport, and Ferrel Osborn . It was concluded that elephants use their powerful, deep calls in lengthy distance communication to coordinate group actions and to find people in reproductive condition. Fascinating observations of elephants within the extremely dry region of Namibia, by Michael Garstang and colleagues, suggests that they could use the infrasound produced by distant thunderstorms to find water throughout drought durations . The discovery of infrasonic communication amongst elephants got here from a hunch Katy Payne had while visiting the Washington Park Zoo in Portland, Oregon.

That’s also true of the standard sound card; I’ve learn they usually start rolling off beneath 10 hertz. This is barely “infrasound” but it is fairly interesting, nonetheless. How totally different is that this discovering from what has been discovered with savannah elephants?

I used a thirteen gigohm resistor to bias the JFET and working against the 100 pF diaphragm capacitance I calculate a -three dB frequency of a hundred and twenty mHz. That seemed a bit excessive to me considering the microphone mechanical response is probably well beneath that.

  • The native velocity of infrasound in air at ambient temperatures near 20°C (sixty eight°F) is about 340 m/s (1115 ft/s), the same as for audible sound.
  • Earthquake and seismic waves are elastic waves which happen at infrasonic frequencies in the Earth’s crust and within the oceans and seas.
  • The bodily laws of propagation within the environment are basically the same as for audible sound.

A tighter diaphragm will lower the sensitivity a bit and improve the excessive frequency response plus add to the usable lifetime. I used styrofoam spray adhesive and silicone caulking to seal it however I did not seal the wires going from the microphone to the telephone jack. (Behind the microphone out of view is a freshly baked large desiccant bag.) Wind hitting this case will cause strain adjustments inside so another layer or two is a good suggestion. I simply put this thing underneath a plastic trash can with a rock on prime and that’s under a patio.

I mounted the amp and microphone in a wall phone jack, wrapped it in nice material (clear room wipe) secured with electrical tape. The fabric is just to maintain out curious insects – in all probability not essential.

Also, the larger that bias resistor, the decrease its noise contribution at a particular frequency above reduce-off. (The capacitance rolls off the resistor noise sooner than it will increase due to resistance at a particular frequency.) HOWEVER, I did a quick experiment and decided that it’s most likely a good suggestion to leave things as-is. That’s good news for the experimenter since 10 gigohm resistors are fairly low-cost at Digikey and Mouser.

Examples Of ‘Infrasound’ In A Sentence

I made ashort video of this circuit driving a speaker at about 1 Hz and an oscilloscope at 0.1 Hz. There’s a little distortion as I forgot to decrease the amplitude a tad, it’s simply barely clipping at full degree into an eight ohm speaker.

Experiments in the savannah had been largely performed beneath optimum environmental conditions with little or no wind. There are some theoretical reasons to suppose that animals are very good at extracting acoustic signals from the background, so forest elephants would possibly do much better than we assumed.


I initially watched the output on a scope with no amplification. But I need to add an amplifier at the microphone for driving the cable because it tends to select up noise as-is. I’ll be discussing the electronics in additional element in the future.