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hearing infrasound

Michael Forrest michael_forrest at lineone.net
Wed Mar 15 17:20:25 EST 2000



Vic Tandy <v.tandy at coventry.ac.uk> wrote in article
<38CFBE48.F2F4C320 at coventry.ac.uk>...
> I have been doing some research on the effects of Infrasound (below
> 20Hz) on humans. It seems to be thought generally that if infrasound has
> an affect on humans at all,it is by resonating with various organs.
> However I would like to find out more about what the hearing system does
> with low frequencies. Does it simply not respond at all or is the signal
> passed to the brain and then ignored unless the signal is very loud.
> Infrasound can be heard / percieved as long as it is loud enough, at
> 20Hz the sound pressure level needs to be above 85dB which suggests the
> mechanism will work if it is pushed hard enough. Does anyone know of
> research in this area? 
> 
yes there has been some, the usual literature search procedure should find
it, as a start look up articles by Yeowart which IIRC looks at auditory
response at frequencies below 20 Hz.

One curiosity of low frequency sound is the steep growth of loudness, ie
inaudible to subjectively loud over a quite small range of physical
intensity. 

Incidentally I suspect this figure of 20 Hz is a bit of a red herring,
there is no definite dividing line and 20 Hz (more or less) just seems to
be about right as a practical working figure. 

Watch out for harmonics which may be heard even if the fundamental isn't
(but I suppose you have already thought of that). 

Why are you interested? there is a suspicion that very low frequency noise
as an environmental stress could be important, but it's hard to be sure.
One thing seems definite, if you have a very low frequency sound which is
causing annoyance, the "A" weighting can mislead!

regards, Mike






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