THE SCIENCE AND APPLICATIONS OF ACOUSTICS - H. H. Arnold ...

328 13. Criteria and Regulations for Noise ControlFigure 13.4. Room criterion (RC) curves.of Figure 13.4. The rating number of the resulting balanced noise criterion (NCB)curve, shown in Figure 13.5, represents the arithmetic average of the octave-bandlevels with center frequencies of 500, 1000, 2000, and 4000 Hz. Figure 13.5 isuseful for rating air-conditioning noise in buildings. Table 13.2 (Beranek andVer, 1992) lists the recommended categories of NCB curves for different uses ofbuilding interior space.Example Problem 3In Figure 13.5, the background noise spectrum from air conditioning is plotted as adashed line. Find the NCB rating and comment on the noisiness of the equipment.SolutionWe note that this plot is tangent to the NCB-40 curve and no octave-band levelexceeds this curve. This is a spectrum that might be acceptable for a business officebut is barely acceptable in a bedroom or a residential living room. According toTable 13.2, the NCB-40 rating is not at all acceptable in a concert hall, theater, ora house of worship.