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In two studies twelve subjects were exposed to different types of ventilation noise in a simulated office. In Study 1, a ventilation noise with a gradually falling frequency/level spectral character, was considered as more annoying than a ventilation noise with a band of raised levels around 43 Hz and in particular a tone at 43 Hz. The differences in acceptable comfort levels were aproximately 7 dB when comparing the tonal and gradually falling frequency/level ventilation noise. The frequency character thus has to be considered when evaluating the annoyance due to ventilation noise. The result from Study 2 gives support to the suggested lowering of the highest acceptable level of ventilation noise from 40 to 35 dB(A) and that the level should be reduced even more in environments designed for intellectual work.

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The relationship between low frequency noise exposure and subjective symptoms, such as fatigue, tension, irritability and annoyance reactions were studied in a group of 439 persons working in offices, laboratories and industries. Measurements were made of each person's exposure to noise and subjective responses were collected by means of a questionnaire. The dB(C) – dB(A) difference was used as an indicator of the low frequency character of the workplace noise. Indices of annoyance, distraction reactions and symptoms were used as dependent variables in hierarchical multiple regression analyses. Potential confounders were controlled for. Low frequency noise was strongly related to fatigue and tiredness after work, with an increase of these symptoms with increased low frequency dominance in the noise. Annoyance was strongly related to noise level and distraction reactions were neither related to noise level nor with the low frequency character of the noise. Specific response patterns due to low frequency noise are discussed.

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