NR Curves

The NR curves are similar to the NC curves (see Figure 6.7). They were originally produced to develop a procedure to determine whether noise from factories heard in adjacent apartments and houses is acceptable [26]. The noise spectrum is measured and plotted on the family of NR curves (Figure 6.8) in just the same way as with the NC curves. One difference from the NC curves, however, is the use of corrections for time of day, intermittency, audible pure tones, fraction of time the noise is heard, and type of neighborhood. These corrections are made to the final NR rating and not to the one-octave band levels used to determine the NR. It has been found that in the range of NR or NC of 20 to 50 there is little difference between the results obtained from the two approaches.