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I <br />The levels associated with environmental noise, in almost every case, produce effects only in the first two <br />categories. Workers in industrial plants can experience noise in the last category. Unfortunately, there <br />is as yet no completely satisfactory way to measure the subjective effects of noise, or of the <br />corresponding reactions of annoyance and dissatisfaction. This is primarily because of the wide variation <br />in individual thresholds of annoyance, and habituation to noise over differing individual past experiences <br />with noise. <br />Thus, an important way of determining a person's subjective reaction to a new noise is the comparison <br />of the existing environment to which one has adapted: the so-called "ambient'. <br />In general, the more a new noise exceeds the previously existing ambient noise level, the less acceptable <br />the new noise will be judged by the hearers. <br />With regard to increases in A -weighted noise level, knowledge of the following relationships will be helpful <br />in understanding this report. <br />• Except in carefully controlled laboratory experiments, a change of 1 dB cannot be perceived. <br />• Outside of the laboratory, a 3 dB change is considered a just -perceivable difference. <br />• A change in level of at least 5 dB is required before any noticeable change in community <br />response would be expected. <br />• A 10 dB change is subjectively heard as approximately a doubling in loudness, and would almost <br />certainly cause an adverse change in community response. <br />1 <br />ER -93-1 - 75 - (9-27-93) 1 <br />