Explanations of annoyance from low frequency noise at very low levels

A questionnaire study comprising about 200 people who report annoyance from low frequency noise or infrasound has been carried out at the Section of Acoustics (see 'Related projects': "Cases of Annoyance from Low-Frequency Noise and Infrasound". The study found, largely in accordance with previous empirical findings, that subjects report annoyance and several effects on health and well-being, although the sound pressure levels measured generally have been rather low and sometimes not exceeding the normal perception threshold. The study has raised the questions, whether the reactions are caused by a physical sound, and, if so, whether the sound levels are correctly measured. Other questions are, whether the perception and initial reactions can be explained by physiological irregularities related to the hearing function such as exceptionally good hearing, a low perception threshold within certain frequency areas, a steep increase in subjective loudness (recruitment-like phenomena). Sound measurements have been undertaken among a randomly selected sample of 21 subjects that previously have answered the questionnaire on low frequency noise. These subjects have undergone clinical testing of hearing and vestibular functions at a medical clinic. They have then undergone further examinations at the Section of Acoustics, including investigations of perception thresholds, loudness perception and recognition of different sounds. The investigations have been possible due to the completion of the test facilities for reproducing free-field low frequency sound at the section (see Related projects: "Testfacility for Correct Free-Field Reproduction of Low Frequency Sound"). The results from the project showed that one-third of the subjects are annoyed by a physical sound, while another third are annoyed by a sensation of sound generated in the hearing mechanism, ‘low-frequency tinnitus'. The subjects who are annoyed by a physical sound do not have an exceptional good hearing, but unreliable measurement methods and normal individual differences in the hearing between people can explain why these cases previously have been "unexplained". The results were released in 2007 and the final documentation was made and submitted for publication. It will be published in the first half of 2008.. Supported by STVF/FTP and Marie & M. B. Richters Fond.