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I am suffering from a strange hum in my home. I have just bought my home and living in 3 months. A month ago I've started to hear a humming noise. Then, I recorded the sound and looked at its frequency response. The peak was at 50 Hz. After a while, I started to use an application named "SignalScopeX" for iPhone. It gave me the same results, in this app you can see the response in real time and there is a peak at exactly 49 Hz. I measured several times (in night and day) and the sound exists every time. Is there a possibility that in pure silent mics response 50 Hz, or is it real sound? I hear it but still I want to be sure about that. I suspected an electrical machine vibrating my walls (I am living in Turkey, main electricity is 50 Hz). Me (living in 6th floor) and my neighbours (living in 5th and 7th floors) cut of our home electricity but still, the sound is exists. What can be the reason of the sound?

Some of my thoughts are:

  1. There may be a constant working motor like an aquarium on the 10th floor. Is it possible?
  2. There is a general electricity line of building in one of my room. If there is any leakage may it cause the sound? How can I measure it? Are there any more possibilities?
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  • $\begingroup$ If something is causing vibrations to get into the frame of the building, the sound will be heard everywhere but the source could be anywhere. I don't think it is likely to be caused by "electrical leakage" (whatever that means) but sounds like this can certainly be real, hard to track down to the source, and hard to eliminate even when you know what the cause is. $\endgroup$ – alephzero Apr 4 '19 at 14:01
  • $\begingroup$ 49Hz is just about right for an induction motor running off of 50Hz mains. As @alephzero mentions, the source could be anywhere in the building. All it would take would be a motor firmly mounted to the building frame, and a bit of mechanical imbalance. $\endgroup$ – TimWescott Apr 4 '19 at 17:20
  • $\begingroup$ Somewhere in the building is a "house panel". Try cutting that one - at 3 am when wearing gloves and a hoodie. Just kidding. Instead, read the breaker labels on the house panel and note likely suspects. My money's on niels's booster pump. $\endgroup$ – Phil Sweet Apr 4 '19 at 23:31
  • $\begingroup$ 50 Hz is puzzling. I would expect most energy at 100 Hz or some higher harmonic. It's like there's a loudspeaker spitting out mains hum, not a transformer or motor. $\endgroup$ – D Duck Apr 7 '19 at 23:02
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Some large buildings have a transformer attached to them for the mains supply for all apartments. The vibrations are probably being transmitted via harmonic resonance due to acoustic amplification. This may have been why previous owners sold the property.

Human body operates at 25Hz which means harmonic octave frequencies are more noticeable to us. It may be possible to use noise cancelling sound to negate the impact and an audio specialist may be able to help out with creation of an inverse sine wave oscillator.

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Indeed, if the spectral content of the noise is peaked at the mains frequency, it is evidence of a motor somewhere in the building that runs all the time. This could be a ventilator or exhaust fan for a kitchen or bath, an aquarium pump, a refrigerator, or a component of the plumbing system that either boosts the water pressure for the upper floors or scavenges sewage from them.

If that motor is well-coupled to the frame of the building, you will hear it almost everywhere, so I would recommend walking through the building with your sound meter app running and check the basement, attic, hallways, lobby, etc. Somewhere you will find that motor!

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It does "sound" like it could be from an electrical device assuming you are in region that used 50 Hz power. If you are able, try turn off the power at the circuit breaker panel one circuit at a time and see if the sound goes away. That would help limit your search for the cause.

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In addition to a motor, a transformer carrying a relatively high current at 50 Hz can also be a source of mechanical vibration.

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  • $\begingroup$ But would likely produce a hum at 100 Hz. $\endgroup$ – D Duck Apr 7 '19 at 23:04
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Probably it is a small transformers or even an abandoned electrical door chime.

You can try both closing the electrical breakers one by one and or using a stethoscope or directional mic to pick up the location of it. It may well have been buried under some cabinetry or tile work.

If it is actually shorted by connection with a pipe or similar conductor, you pay the utility bill for it. Use magnetic Ohmmeter to find it.

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