(C)2006 by T.J.Moir. All rights reserved.
For some time now there appears to be certain people who have sensitive hearing that can hear a low frequency humming
noise late at night or in the early hours of the morning. The problem appears to be all over the North Shore of Auckland.
We don't know the origin of the generic hum which appears to be world-wide.
Download and listen to the Auckland North Shore Hum in stereo.Quite a few people have said that this is what they hear (minus the cracks and pops caused by noise).
I recommend that you do not listen too loud.You need lots of bass.
Recommend you use headphones if possible.Note - cheap speakers built into an LCD screen or equivalent will probably not play this sound.
You do need reasonable quality speakers or headphones.The actual hum sounds just like this except the level is very low making it very hard to pick up
except those with good hearing. Late at night it appears to waken some people.
If you get troubled here are a few suggestions...Try playing a CD of rainfall (they are available!) or similar which should
mask the sound.You can try sleeping with a fan on if you don't mind the sound of the fan.Alternatively there is a link below
to an entirely new method to help you sleep with the hum problem. This is a 16 bit stereo .wav file which has not been compressed in any way.
Power spectral density is the average power in the signal (for one channel here) plotted versus frequency.It is sometime known as
periodogram since it is in fact a digital estimate and not a true analogue power spectrum. The power spectrum was obtained by succesive
averaging over blocks of FFT (Fast-Fourier Transform) estimates. Thank you to the following people - Dr F.Alam,Phil Strong and
Ms Nair Mana Tsuji.Special thanks to all the NZ residents and overseas sufferers of the Hum who have contacted us.
Note:For the power spectral density graph as shown here and in the London Times - dB as used in Elect Engineering is a relative thing.
Don't confuse the scale with standard sound pressure readings or you will think the hum is deafening! The spectrum is important
in that we can see that a harmonic is so many dB down on a fundamental - it is relative and not absolute to any reference.
The map below is not complete - there are parts where there is hum not shown - Devonport,Grey Lynn,Westmere,Herne Bay.Also further north in Whangaparoa -Stanmore Bay.
An approx 3 min MP3 stereo of the Hum in Glenfield. On March 23rd 2007 Brendan Clark of Howick(Auckland) recorded the following which may well also be the hum.
Nobody else could hear it in his house until he recorded it. It is recorded at 16 bits 48kHz mono.
Download Howick Recording.
Latest: In mid March 2007 Nair Mana Tsuji (who has been to a great many of the houses) tested a Faraday Tent.
A Faraday tent is a bit like a Faraday cage except it is portable. Look at this link (NOTE - FIREFOX does NOT work - it misses most of the page
- you have to use IE) for details.
Faraday Tent (single layer).
This tent at 1MHz has an attenuation of 20dB going up to 60dB at 500MHz-1GHz (the mobile phone region is near 1GHz).
It goes on working to about 2.5GHz. The news is that Nair could still hear the hum clearly in this tent indicating that microwaves
for mobile phones and the majority of other comms systems are not to blame.eg wi-fi,bluetooth,LANs,3G etc. This would not block ordinary AM
radio of course since the carrier is less than 1MHz.(or VLF for submarines). TETRA uses bewteen 380 and 395 MHz and between 410 and 425 MHz
and so we can rule out TETRA once and for all. Nair reported that there was no attenuation in the hum though
of course her mobile phone did not operate within the tent indicating the tent does work.
What the hum probably isn't - some notes - far from difinitive though:
Mains Hum (since it isn't 50Hz and the resolution of our equipment is 0.1Hz)
Radio frequency mobile phone transmitters or Tetra - since it is acoustic
H.A.A.R.P (HIGH FREQUENCY ACTIVE AURORAL RESEARCH PROGRAM.Since the world Hum pre-dates this project)
A secret military weapon (one of our group works for the military and is just as puzzled!)
What it probably is or behaves like:
A natural phenomena of some sort, acoustic in nature.
Like blowing over a bottle (or listening to a shell)
It gets stronger with lower air pressure
most of the houses here in NZ that have hum lie in a dip in the ground off the road
Natural occuring phenomena that causes hums (but not THE hum!).
Mains Hum at 50Hz from transformers.(note - NZ is 50Hz, NOT 60Hz)