The Bristol Hum

I moved to Bristol just over four years ago. I hear The Hum. In fact, I can hear it right now as I type at 11am on a sunny March morning.

In the past four years I lived in a first floor flat of an old building, built circa 1850. I always thought the noise I could hear was something to do with the neighbours, perhaps a heating system, tumble drier, or desk fan. I got to know my immediate neighbours well (above and below) and possible causes such as those mentioned above were swiftly ruled out. The adjoining neighbours were separated by a very solid and thick wall, but I assumed the noise must be from them. The hum wasn’t consistent between 2013–2017, but I could hear it most of the time.

What does it sound like?

To those who can hear it, the noise can be infuriating, especially as it seems much more prominent at night, likely due the any background noise being minimal. I can attest to the common descriptions; a diesel truck idling down the road; the distant rumbling and occasional oscillation of a common desk fan, perhaps bolted to a wall; an amp left switched on, etc. It’s a low frequency hum, that is what it is.

  • Oscillating Desk Fan
    An oscillating fan
  • Amp
    An amp
  • Truck
    A truck

While away travelling last year, in New York, Prague, and the South of France, I didn’t hear the hum, but I have heard it in London. The sound can be masked by things like; white noise, music on headphones, central heating, fridge cycles, etc.

New Home

I recently moved home, very close to my old flat, but this time on the ground / garden level with the home’s elevation higher this time, up a small hill. I mention this because there are reports that the sound is more noticeable on hills as opposed to in valleys. Again, the building is old, circa 1800, but has been modernised over time. The subfloor is concrete, I have no idea how the foundations were laid.

The hum here is very prominent, in fact in the 6 weeks or so I have been here I can account for only one occasion where the noise completely disappeared… one Sunday morning three weeks ago. My initial feeling is that the vibration is coming from the ground, through the foundations, and can be heard through the structure of the building. This would make sense as to why I could often hear it in my previous flat.

Initial Research

I began to research the phenomenon and quickly discovered that The Hum was not exclusive to Bristol with reports coming from all around the planet. The World Hum Map is a resource for people to report the noise and is doing a great deal to collate data. I’ve linked to some interesting pieces of information I’ve found below.

So What Is it?

  • Cat Red Dwarf
    “So what is it?!”
  • Ocean Waves
    Ocean waves?
  • Mobile phone mast
    Mobile phone masts?

Here are a few things suggested over the years (links are to Wikipedia articles):

While some of these border on the ridiculous there is definitely something going on here. I’d love to know what it is and also why some people just cannot seem to hear it. I wouldn’t be surprised if there’s a perfectly good scientific reason like the Schumann Resonance theory.

Audio Recordings

Last night I managed to capture The Hum. I used my Rode NTG2 Shotgun Condenser Mic and a Zoom H4N recorder. The recordings were made in my bedroom between 0030–0200 apart from the hum, it was quiet… my central heating was off, the takes were made in-between the fridge’s cycles in the kitchen, I was creating no noise myself, the neighbours were quite, and there was no car traffic on my road. Nb. my bedroom has double glazed doors and it located at the back of the property.

  • Frequency Analysis
    Frequency Analysis
  • Noise Reduction
    Noise Reduction
  • Parametric EQ
    Parametric EQ

Using Adobe Audition I filtered out the higher frequencies, leaving apx. 200Hz and lower. As you can see from the frequency analysis, there’s a lot going on down there. I’ve posted the exact steps I used below in case anyone else wants to replicate them.

  1. Noise Reduction (process). To reduce the mic floor hiss.
  2. Parametric Equaliser. To isolate low frequencies. Gain set to 35dB
  3. Channel Mixer. To boost the sound a bit more.

In the linked .zip file you will find one of the recordings I made, including;

  • the original .wav file
  • the Adobe Audition .pkf
  • the processed audio using the steps above

Nb. You will need half decent headphones to hear the frequencies properly, i.e, I’m, using a pair of KRK KNS-6400.

Having captured the low frequencies has empirically confirmed my doubts that this is related to tinnitus, for me at least. I’ve also posted a video of the processed audio and the Frequency Analysis.

Please let me know what you think in the comments, suggestions, thoughts, etc.

Research Links

The Hum on Wikipedia
https://en.wikipedia.org/wiki/The_Hum

The World Hum Map
http://thehum.info

Article on BBC Future which inc. a 12 min. documentary (12th August 2016)
http://www.bbc.com/future/story/20160811-the-mystery-noise-driving-the-world-mad

The BBC Future film was recently uploaded to BBC Earth Lab on YouTube (7th July 2017)
https://www.youtube.com/watch?v=QpeKot2X_O8

World Hum – New “Schumann Resonance theory” (27th Sep 2015)
https://youtu.be/MJkcHwvKdv8

Bristol hum: Council investigates mystery noise (19th Jan 2016)
http://www.bbc.co.uk/news/uk-england-bristol-35353241

The strange case of the Bristol hum (19th Jan 2016)
http://www.bbc.co.uk/news/magazine-35344544

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