Just had a great conversation with Sarah Angliss (http://www.sarahangliss.com/) who amongst god knows how many other cool things did a project using infrasound (http://www.sarahangliss.com/infrasonic-the-pipe). She was kind enough to take some time out and chat me through things. Some sound advice on safety (sorry bad pun) i.e. you might not be able to hear the sound but it can still be very loud, so for goodness sakes measure your DBA carefully. Equally when you are measuring things make sure the Mic you use and any device in the chain producing the audio is carefully selected. It sounds like its easy to mask or fail to produce the lower frequencies. On top of that I now have Eigen Frequencies (http://en.wikipedia.org/wiki/Eigenvalues_and_eigenvectors) or Room Modes (http://en.wikipedia.org/wiki/Room_modes) to investigate and possibly a bit more reading on Nystagmus (http://en.wikipedia.org/wiki/Physiologic_nystagmus).

Posted by tomburton