Infrasonic Measurements - Inter-Noise 73
By Per V. Brüel and Hans P. Olesen.
This paper comes from Dr Malcolm Swinbanks, Acoustician, UK, who wrote on March 15, 2016:
“As I had commented before, the first author Per V. Bruel was one of the two founders of Bruel & Kjær, which is still regarded as a world leading manufacturer and supplier of acoustic and vibration measurement instrumentation.
“So this 1973 paper would be regarded as having been written by two extremely skilled measurement acousticians of the time.”
Lately, there has been an increasing interest in the sound at very low frequencies. Several articles describe the low frequency sound which exists in the ocean and is found all over the world. Infrasound is also found in the atmosphere with variable strength. One source of this sound is thunderstorms. These may take place far away from the places where the infrasound is noticed, and this is because the damping of the low frequency sound is very small compared with the attenuation in the air of normal audible sound.
However, there are other interesting phenomena connected with low frequency sound, e.g., a large manufacturer of aeroengines has a problem concerning an indisposition among his office personnel, which was believed to have some connection with the low frequency sound from engines running in test beds.
A similar thing happened at the aeroengine manufacturer's plant, where the head of the office did not believe in the complaints of his office staff, so he installed himself in the office where the complaints had been most severe, in order to demonstrate that the whole thing was nonsense, but after some time he felt seasick himself.
The measurements have confirmed that significant infrasound levels do exist, especially in man made environments. There is also a strong indication that even low sound levels, at low frequencies may cause unpleasant effects on human beings. No attempt shall be made here to point to specific threshold levels, as the test material is so limited and as all test parameters are not known. However, as even convinced sceptics were influenced to feel sea-sick at moderate infrasound exposure there seems to be a great need for further investigation into the topic.Full paper