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Laboratory Evaluation of Annoyance of Low Frequency Noise 9. ConclusionA laboratory investigation of the annoyance of low frequency noises has been performed. Eighteen normal hearing test subjects listened to eight different noises and evaluated the loudness, the annoyance at day/evening and the annoyance at night. All noises had a considerable low frequency content. The evaluations were compared to the noise limits and criteria curves for low frequency noise used in the European countries. As a pilot project, a group of four persons – who were known to experience problems with low frequency noises – participated in the same listening test. The results show that the Danish measuring method describes the subjectively experienced annoyance better than the measuring methods used in other countries. This result relies on the 5 dB impulse noise penalty included in the Danish method. The decision about whether or not a 5 dB penalty shall be applied to a specific noise is based on a purely subjective judgment and therefore the Danish method could be improved at this point. The Swedish method is almost as good as the Danish method if the (impulsive) discotheque sound is omitted from the analysis. The Swedish method is based on a specified criterion curve (in contrast to the Danish noise level calculation) and as such more sensitive to random measurement uncertainties. Because the traffic noise was outdoor-to-indoor filtered, the traffic noise did not serve as a reference noise as originally intended. This also prevented a comparison of the present findings to ordinary traffic noise annoyance investigations from the literature. An almost perfect correlation was found between the annoyance at day/evening and the annoyance at night. The annoyance at night is slightly lager than the annoyance at day/evening. The difference in the annoyance ratings between day and night corresponds to a level change of about 5 dB. The low frequency hearing threshold of the four special test subjects was not found to be better than the hearing threshold of the ordinary test subjects. The annoyance evaluations made by the four special test subjects were clearly different from the evaluations made by the ordinary test subjects. The ratings were systematically higher. Especially at night the annoyance was rated as close to maximum and thus not dependent on the level of the noise. The four special test subjects were not annoyed by the impulsive noises to the same degree as the ordinary test subjects were. The Danish evaluation method seems to be suitable for predicting the annoyance experienced by the general population. It seems to be is less suitable for predicting the annoyance experienced by the special subject group where the influence from the noise level is less pronounced and where individual reactions to the quality of the sounds becomes more important.
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