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Not sure whether this is the right place, but we've recently in our house been aware of what feels like an ultra low frequency infrasound. It's almost like an engine idling, you don't so much hear it as feeling it, and it's really starting to get on our nerves. It will lead to us feeling on edge, more irritable, and while unconfirmed I fear may interfere with sleep cycles. I have a few culprits in mind which could be causing it, but can think of very few ways to further narrow it down. Our AC is my prime candidate for it so far.

Is there any way without spending a huge amount of money so that I can set something up to detect this sound, and possibly allow me to track its origin by understanding where it is loudest? I understand the medium here is the most serious concern, however it can be heard only in a single room of the house when sitting there, which means it's at least being transferred somewhat by the air of the room. Maybe possibly a microphone set to isolate any noise over a certain wavelength could possibly be the way?

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  • Sounds like you could be feeling the approx 30Hz rumble that Benn Jordan felt in Louisiana. He made a video about his research and theories: youtube.com/watch?v=zy_ctHNLan8 I don't think he used ultra-special microphones, but he probably had very quiet electronics. He didn't list his equipment in the video's description, but he may answer questions about it.
    – Sotto Voce
    Mar 17 at 17:13
  • Help us help you by clarifying your question: are you trying to identify the source of the sound or wanting to study it? My answer below assumes the former, but since you didn't respond, I'm unsure what you need.
    – MadMonty
    Mar 22 at 14:29
  • I remember years ago, I saw a TV segment about people living in a certain area in the US could hear a LF droning sound which is not initially noticeable. For you, it could be that the room is the right dimensions to amplify the sound (see "standing waves"). I'd be interested to hear if there are canyons nearby.
    – n00dles
    Mar 25 at 16:39

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To determine the cause, you don't need instrumentation if you are pretty sure you can tell when the problem is present and when it's not. (If you're unsure, see below for instrumentation example.)
Here's what you can do to sort it out:

  1. begin with the low-hanging fruit, the electrical appliances in your house, and systematically shut each one off. For example, shut off the suspect HVAC system. If that stops the noise, you may still want to break down whether it's caused by the air handler/ductwork system, or the compressor.
  2. You can differentiate by putting the blower in "continuous" mode and switchiing the heating and cooling components off and on. (Do that by setting the thermostat very low for AC or very high for heat, so it won't come on. If the sound goes away, then set the thermostat the other way to activate the compressor/heater to confirm that's what was causing the sound.
  3. If either of these is the culprit, either call in the HVAC service or post another question asking how to mitigate the noise. You may also want to post in Home Improvement.
  4. If none of your appliances is involved, repost with details about when and where you detect it.

You would do well to check this out: When I started working in a computer main frame room in a medical college, I often felt something was amiss that I couldn't pin down. I borrowed an audio spectrum analyzer that went down to 20 Hz, lower than what most of us can hear. It revealed a subsonic rumble which was traced to the air handlers cooling the computer gear. They created a subsonic pressure wave not unlike what you suspect. It was hard to describe the effect; you couldn't hear it, but you felt something was wrong. I made a trip to the medical library, where I found several journal articles tying this kind of subsonic vibration to stress with consequent long term health effects.

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