Objectives: The aim of the study was to recommend methods for assessing low frequency noise (LFN) in the occupational environment to prevent annoyance and its effects on work performance. Three different evaluating methods and corresponding admissible values were proposed: (i) method I--frequency analysis in 1/3-octave bands within the range of 10-250 Hz, (ii) method II--consisting in 1/3-octave band measurements and determination of low frequency equivalent-continuous A-weighted sound pressure level (SPL) in the frequency range of 10-250 Hz, and (iii) method III--based on equivalent-continuous A-weighted SPL corrected due to the presence of low frequencies and tonal character of LFN. Separate noise limits were recommended for workplaces in control rooms and office-like areas.
Materials and methods: The proposed criteria were verified in laboratory and field studies. The laboratory study included 55 volunteers, aged 21.8 +/- 2.1 years, with normal hearing (< 25 dB HL). The subjects listened to different noises at A-weighted SPL of 45-65 dB, and evaluated annoyance using a 100-score graphical rating scale. In the field study, 35 male workers, aged 40.1 +/- 7.2 years, exposed to LFN at A-weighted SPL of 48-61 dB, were asked to rate noise annoyance at their workplaces using a similar graphical scale. The subjective ratings of LFNs were compared to objective results from various assessing methods. The relations between annoyance and excesses of proposed limits were analyzed using Pearson's correlation coefficient (r).
Results: Linear relationships between the subjective ratings and results from all proposed exposure criteria were observed (0.550 < or = r < or = 0.673; p < 0.001). In the field conditions, however, the highest correlation coefficient was found for method II (r = 0.673), while during the laboratory study for method I (r = 0.612) and criterion curves based on hearing threshold level (HTL).
Conclusions: All proposed criteria, especially the evaluation method based on the low frequency equivalent-continuous A-weighted sound SPL (method II) as well as the frequency analysis in 1/3-octave bands 10(20)-250 Hz (method I) and criterion curves based on HTL or A-weighting characteristics, seem to be able to quite well predict annoyance experienced from LFN at workplaces.