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

330 13. Criteria and Regulations for Noise ControlTable 13.2. Recommended NCB Curve Categories on the Basis of Interior Use andSuggested Noise Criteria Range for Steady Background Noise.ApproximateType of Space (and Acoustical Requirements) NCB Curve a L A ,dBBroadcast and recording studios (distant microphone pickupused)Concert halls, opera houses, and recital halls (for listening tofaint musical sounds)Large auditoriums, large drama theaters, and large churches(for very good listening conditions)Broadcast, television, and recording studios(close microphone pickup used only)Small auditoriums, small theaters, small churches, musicrehearsal rooms, large meeting and conference rooms(for very good listening), or executive offices andconference rooms for 50 people (no amplification)Bedrooms, sleeping quarters, hospitals, residences,apartments, hotels, motels, etc. (for sleeping, resting,relaxing)Private or semiprivate offices, small conference rooms,classrooms, libraries, etc. (for good listening conditions)Living rooms and drawing rooms in dwellings (for conversingor listening to radio and television)Large offices, reception areas, retail shops and stores,cafeterias, restaurants, etc. (for moderately good listeningconditions)Lobbies, laboratory work spaces, drafting and engineeringrooms, general secretarial areas (for fair listeningconditions)Light maintenance shops, industrial plant control rooms, officeand computer equipment rooms, kitchens and laundries(for moderately fair listening conditions)Shops, garages, etc. (for just acceptable speech and telephonecommunication). Levels above NC or NCB 60 are notrecommended for any office or communication situation.For work spaces where speech or telephone communication isnot required, but where there must be no risk of hearingdamage.10 1810–15 18–23Not to exceed 20 28Not to exceed 25 33Not to exceed 30 3825–40 38–4830–40 38–4830–40 38–4835–45 43–5340–50 48–5845–55 53–6350–60 58–6855–70 63–78a See Figure 13.5.This averaging time T can be chosen to be anywhere from a few seconds tohours. L eq can be readily measured through the use of an integrating sound levelmeter. Because it takes into account both magnitude and duration, the equivalentsound level has proven to be a viable parameter for evaluating environmental noisefrom industry, railroads, and traffic. L eq is found to correlate very well with thepsychological effects of noise.In order to account for different response of people to noise at night, the U.S.Environmental Agency developed the day–night equivalent level (DNL), as defined