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I've been hearing this strange continuous hum in my apartment for a while now. It is a small apartment and the hum is present all throughout with varying intensities, so I can't really infer from which direction or room it is coming from.

I used an app from my phone to measure it and found it to be around 587Hz (image attached,) so clearly it wasn't tinnitus. I found from google searches that appliances and mains can hum, but at the frequency of the AC power supply, which at my place is only 50Hz.

I am trying to find the source of this annoying hum so I can repair it.

Can a sound of this frequency be generated from electrical appliances or faulty connections?

Update: Since it had been just been a week since I rented this apartment, after searching around I found a switch that cuts off the power to the whole apartment. (Looks like a pretty normal switch.) It turns out that turning it off doesn't affect the sound, so I am guessing it's from one of my neighbour's but I can't seem to hear it when I step outside. Since this is a pretty crammed building I couldn't really track the sound from anywhere else.

enter image description here

JRE
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Discord Warrior
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    Musical note D5, coincidentally. – Tom Carpenter Aug 01 '21 at 10:04
  • Is it continuous? And constant and widespread? You haven’t given much detail. There are also motor bearing resonances – Tony Stewart EE75 Aug 01 '21 at 10:12
  • @TonyStewartEE75 Yes, it is continuous. It's a small apartment so it's audible all throughout. Thanks for pointing it out, I will add it to my question. – Discord Warrior Aug 01 '21 at 10:20
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    generally sounds get loader as you approach the source. use you sound meter to find where it's loudest. check your front door, your neighbours front doors, the floor above the floor below etc. – Jasen Слава Україні Aug 01 '21 at 10:23
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    Could it be an indication of bearing noise fatigue? Call Maintenance. Mixing it with a stable 500 Hz to see phase noise indicates if it is mechanical from variations. This method is used to analyze harmonics in turbines, ball frequency will be a harmonic of RPM – Tony Stewart EE75 Aug 01 '21 at 10:32
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    There are ways to get mains audio harmonics, for instance a transformer magnetostricting, but I'd expect the frequency to be more accurately 550 or 600 Hz, assuming your phone app is not wildly out on frequency. Maybe look for 'organ pipe' resonances in air ducts or water pipes. – Neil_UK Aug 01 '21 at 10:45
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    If you make the assumption that the major low frequency ridge in your display is much more likely to be 100 Hz rather than the implied 70 Hz or 80 Hz then it's quite possible that your 587 Hz is more like 750 Hz and it then becomes the 15th harmonic of your 50 Hz. In other words, your measurement is suspect and, any answers based on assuming measurement accuracy would have to justify why the measurement you made can be relied upon. – Andy aka Aug 01 '21 at 11:04
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    Try switching off, breakers to different rooms in the house, and the whole house to see if it stops. – AJN Aug 01 '21 at 11:10
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    @Andyaka Yes, It's possible the phone measurement may be inaccurate. Hence I also tried using a frequency generator from my phone. I varied the frequency from 580-590Hz and I was able to hear beats disappear when approaching 587Hz and gradually reappearing on crossing 587Hz (A method I use to fine-tune my guitar). Not sure how reliable of a measurement this is though.Thanks for pointing this out. – Discord Warrior Aug 01 '21 at 11:31
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    Yeah, good shot at a calibration but, if you use your phone for generating and your phone for analysing then they are likely to agree but both might be subject to the same error. – Andy aka Aug 01 '21 at 11:53
  • My first guess would be skip mode at light load for something. – winny Aug 01 '21 at 13:49
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    Can you hear it if you put your head out of a window - as in, could it be a neighbour's air conditioning unit? – Andrew Morton Aug 01 '21 at 13:58
  • Could it be a fan or blower from the HVAC system? – Gil Aug 01 '21 at 22:06
  • 587Hz is a mid frequency, not a low frequency hum. My guess it is caused by wind on a balcony blowing across the open top of an opened beer or wine bottle. – Audioguru May 24 '23 at 20:50

2 Answers2

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In short: yes.

Before fancy power electronics were used in appliances driving motors and whatnot, it was a pretty good bet that any hum that you heard was your local mains frequency or twice that. So, 50Hz 60Hz, 100Hz or 120Hz.

As to where the noise is coming from in your apartment, it sounds like it is coming from outside, possibly a neighbor's apartment or possibly some equipment in your building.

TimWescott
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Just some thoughts.

First, can you hear it from outside your apartment? What about lobbies to the next ones along/up/down? Can you narrow down the place it is coming from?

Try switching off as much electrics as you can, right back at the breaker box. Then back on one at a time.

Do the apartments have a permanent ventilation system, or a permanently-circulating water pump in the plumbing, or something? I am thinking some sort of rotating fan or pump bearing.

I have known fluorescent tubes hum when the electrics are slightly loose. Is there any 24/7 lighting like that?

Switched-mode power supplies (buck converters) can also hum (include cheap LED lights in that), but they are usually higher-frequency than this and laden with harmonics. Maybe a big one looking after an uninterruptible power supply or a solar booster?

Guy Inchbald
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  • Mine is a building crammed with many small apartments, so one of them may have some of the things you mentioned. Also possible the owner has installed a common one for the building. Will go ask around tomorrow.Thanks! – Discord Warrior Aug 01 '21 at 18:37