In the latest SPR Joyrnal there is a paper looking at the acoustics of poltergeist raps taken from various recordings made during the cases (see http://www.spr.ac.uk/main/news/colvin-a ... st-rapping).
The main finding is that poltergeist raps apparently typically take longer to reach a peak sound intensity compared to recordings of similar surfaces being deliberately knocked.
However, if the distance between the recorder and the sound source is a significant proportion of the room size (a few metres in a typical domestic room), the rise to a peak takes much longer anyway. This is because a significant proportion of the sound is actually reflected off the room walls. The result is that sound takes longer to peak while the sound arrives from various reflections as well as more direct routes.
The relatively long distance between the sound source and recorder also results in a loss of the high frequency component of the sound. This was also noted in the SPR paper.
A group of researchers spent a weekend trying various deliberate knocks and comparing the rise to peak with recordings used in the original paper. They found they could easily reproduce the characteristics of the poltergeist raps with ordinary knocks. For more info read http://www.rationalskepticism.org/paran ... 3-400.html
The main finding is that poltergeist raps apparently typically take longer to reach a peak sound intensity compared to recordings of similar surfaces being deliberately knocked.
However, if the distance between the recorder and the sound source is a significant proportion of the room size (a few metres in a typical domestic room), the rise to a peak takes much longer anyway. This is because a significant proportion of the sound is actually reflected off the room walls. The result is that sound takes longer to peak while the sound arrives from various reflections as well as more direct routes.
The relatively long distance between the sound source and recorder also results in a loss of the high frequency component of the sound. This was also noted in the SPR paper.
A group of researchers spent a weekend trying various deliberate knocks and comparing the rise to peak with recordings used in the original paper. They found they could easily reproduce the characteristics of the poltergeist raps with ordinary knocks. For more info read http://www.rationalskepticism.org/paran ... 3-400.html
