On Feb 19, 2:02 pm, [email protected] wrote:

> Mr Thompson said he had established that the noise - which he has
> recorded - has a frequency of about 40 to 42 cycles a second, but such
> a long wavelength that it was virtually impossible to establish the
> direction of the source.
> Intensive research has been conducted into the Cambridge hum by the
> Department of Acoustics at Chelsea College, London. Despite the use of
> directional microphones researchers have so far been unable to detect
> the source of the external hum plaguing the Langs.

In my experience in recording a distant diesel engine, directional
microphones will be no use.

How to find the source:
Get people over a wide area who can hear the hum to listen carefully
outside and estimate the direction it's coming from. I can do that so
it's not hard.
Write down the compass bearing and location of the observers.
Plot those directions on a map. Where the lines intersect is the
source of the hum.
If nobody is interested in even trying this, I suggest you are all
wasting your time.

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