Infrasound — Tutorial and Review: Part 1

Infrasound is everywhere. Even in an environment that is very quiet, infrasound levels of 40 dB(IL) (2–20 Hz) can be measured.

Results from numerous investigations about the influence of infrasound on people and animals have been published during the last 20 years. What all these investigations have in common is that only short time exposures have been investigated i.e. infrasound exposures during minutes or hours.

Discrete frequencies in the range of 4–16 Hz have often been used instead of low frequency random noise spectra. The results of these investigations vary considerably, which may be due to the fact that there has not been equal excitation.

In certain experiments and reports the stimuli spectra are often not accounted for. If they are accounted for this is done inadequately. This is also true for the way the results have been treated. Some conclusions that have been made have to be seen as spectacular! Several scientists have pointed out that the results may be caused by stimulus in the audible range, not by infrasound.

At the conference “Low frequency noise and hearing” (May 1980 in Aalborg, Denmark), where most of the leading scientists of the low frequency area participated, it was stated that there are people who seem to be more sensitive to low frequency disturbances than others. In general, infrasound should not be a direct problem for normal people, which these research results showed. There was full agreement that there is not enough research being done today on low frequency disturbances in the range of 20–100 Hz. These disturbances cannot be sufficiently indicated by measuring the sound level in dB(A). The participants seemed quite convinced that people are irritated by low frequency disturbances both during work, at home and during leisure time. This has not been sufficiently noted.

Most machines in industries and in homes also have frequencies in the region of 50 Hz, e.g. transformers, compressors, diesel- and gas motors, electric motors and fans.

The objective of this work has been to make a comprehensive review, especially in accounting for infrasound levels under normal working conditions and in home environment, both in Sweden and in the rest of the world. Due to the fact that the results from different reports are not uniform and often incomplete, a direct comparison of results is not possible.