Bob Masta skrev:
Hi BobOn 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, HenrikThe 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
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.