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Re: Impacts from ultrasound and infrasound
On 17 Aug 2009 at 9:50, Henrik Møller wrote:
> Bob Masta skrev:
> > On 12 Aug 2009 at 22:04, Henrik Møller wrote:
> >> Hi Amy
> >> Please let me mention the common misunderstanding that the human hearing
> >> "stops" st around 16-20 Hz. We do denote sound below 20 Hz as
> >> "infrasound", but it is not inaudible. Below these frequencies, the
> >> perception changes, and the tonal sensation disappears. But tones at
> >> least down to a couple of hertz can indeed be perceived by everyone. The
> >> lower the frequency, the higher the threshold. The sensation goes
> >> through the ear, not the body as often claimed. I think it is still
> >> unclear, if the sensation is from the cochlear or elsewhere in the ear.
> >> For a fairly recent review, please allow me to promote our article:
> >> Henrik Møller, Christian Sejer Pedersen: "Hearing at low and infrasonic
> >> frequencies", Noise & Health, Vol. 6(23), pp. 37-57 (2004).
> >> The idea of infrasound being inaudible has caused a number of
> >> misunderstandings, in particular in the popular press (but also in the
> >> academic literature).
> >> Best regards,
> >> Henrik
> > The fact that a sound may be processed through the ear does
> > not eliminate other paths, such as through the viscera.
> > There were many tests on the effects of vibration in the
> > early years of space flight, and at visceral resonance
> > frequencies these effects could be profound (nausea, and
> > worse). I seem to recall 7 Hz as being a particular
> > culprit.
> > Best regards,
> > Bob Masta
> Hi Bob
> It is true that very low-frequency sound has other effects than the mere
> perception. One is perceived vibration due to the acoustic exposure,
> others are effects on the vestibular system, which may result in nausea.
> However, these effects only occur at levels much above the hearing
> threshold, and which do not normally occur.
> The particular sensitivity at 7 Hz is pure speculation that the sound
> could interfere with and maybe synchronize brain waves. The idea has
> been brought about by various horror films and newspapers, but there is
> no scientific reference. And plenty of experiments have been made
> without seeing anything like that. We have also measured evoked
> responses to low frequencies, and they turn out as for higher
> frequencies just with slightly higher latencies and broadened response
> Best regards,
Amy's original question was not confined to audition or the
hearing threshold. The 7 Hz phenomenon that I referred to
was probably a fairly large amplitude, but I can't relate
it to "hearing threshold" at that frequency (!). As I
recall, subjects were in a jet pilot's seat atop a shaker
system. The 7 Hz sensitivity was assumed to be purely
visceral, having nothing whatsoever to do with audition...
probably just the effects of mechanical stretching and
scrubbing together of internal organs due to large motions
at the visceral resonance frequency. I have no doubt that
there would have been some synchonization of brain waves,
as a side effect of having one's guts tossed around!
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