> -----Original Message-----
> From: [email protected] [mailto:hum-
> [email protected]] On Behalf Of Matty F
> Sent: Friday, 20 February 2009 6:08 p.m.
> To: Hum Sufferers
> Subject: Re: From 1979
>
>
> 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.
... Certainly not to pinpoint the original hum mentioned, because
frequencies in that order are omni-directional, due to the wavelength.
Unless of course they have significant amounts of harmonic content, which
become increasing directional as they get up to 80-100 Hz.
How this would be localised is level measurements taken over a range of
geographic areas, the louder samples indicating towards where the source is
(or it's direction).
I would expect generators to have some harmonic content, though this what
is most easily filtered in silencers systems.
geoff
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