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
patterns.
Best regards,
Henrik
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