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The levels associated with environmental noise,.in almost every case, produce effects <br /> only in the first two categories. Workers in industrial plants can experience noise in the <br /> last category. Unfortunately,there is as yet no completely satisfactory way to measure <br /> the subjective effects of noise, or of the correspondin& reactions of annoyance and <br /> dissatisfaction. This is primarily because of the wide variation in individual thresholds <br /> of annoyance,and habituation to noise over differing individual past experiences with <br /> noise. <br /> Thus, an important way of determining a person's subjective reaction to a new noise is <br /> the comparison of the existing environment to which one has adapted: the so-called <br /> "ambient". In general, the more a new noise exceeds the previously existing ambient <br /> noise level, the less acceptable the new noise will be judged7by the hearers. <br /> With regard to increases in A-weighted noise level, knowledge of the following <br /> relationships will be helpful in understanding this report. <br /> With regard to increases in A-weighted noise level, knowledge of the following <br /> relationships will be helpful in understanding this report. <br /> 0 Except in carefully controlled laboratory experiments, a change of 1 dB <br /> cannot be perceived. <br /> 0 Outside of the laboratory, a 3 dB change is considered a just-perceivable <br /> difference. <br /> 0 A change in level of a least 5 dB is required before any noticeable change <br /> in community response would be expected. <br /> 0 A 10 dB change is subjectively heard as approximately a doubling in <br /> loudness, and would almost certainly cause an adverse change in <br /> community response. <br /> H-2 <br />