Noise Criteria for Rooms

Noise criteria NC curves can be used to evaluate existing situations by measuring sound levels at the loudest locations in rooms (preferably at user ear height). They also can be used to specify the steady, or continuous, background noise levels (not activity noise from occupants of room) needed to help achieve satisfactory sound isolation, provided levels are 4 to 5 dB below the NC curve at both low and high frequencies. Each NC curve is defined by its sound pressure level for eight octave-band center frequencies. Note that the NC rating for a noise situation usually means the lowest NC curve that is not exceeded by any octave-band sound pressure level.

The table below presents recommended NC ranges for various indoor activity areas. For hearing-impaired persons, specify NC curves that are 5 or more below the criteria presented in the table. It is especially critical to achieve low noise levels at 63 and 125 Hz, where hearing-impaired persons have most of their residual hearing.

Type of Space and Listening Requirements	Preferred Range of Noise Criteria	Equivalent dBA Level*
Concert halls, opera houses, broadcasting and recording studios, large auditoriums, large churches, recital halls (for excellent listening conditions)	<NC-20	<30
Small auditoriums, theaters, music practice rooms, large meeting rooms, teleconference rooms, audiovisual facilities, large conference rooms, executive offices, small churches, courtrooms, chapels (for very good listening conditions)	NC-20 to NC-30	30 to 38
Bedrooms, sleeping quarters, hospitals, residences, apartments, hotels, motels (for sleeping, resting, relaxing)	NC-25 to NC-35	34 to 42
Private or semiprivate offices, small conference rooms, classrooms, libraries (for good listening conditions)	NC-30 to NC-35	38 to 42
Large offices, reception areas, retail shops and stores, cafeterias, restaurants, gymnasiums (for moderately good listening conditions)	NC-35 to NC-40	42-47
Lobbies, laboratory work spaces, drafting and engineering rooms, general secretarial areas, maintenance shops such as for electrical equipment (for fair listening conditions)	NC-40 to NC-45	47 to 52
Kitchens, laundries, school and industrial shops, computer equipment rooms (for moderately fair listening conditions)	NC-45 to NC-55	52 to 61

*Do not use A-weighted sound levels (dBA) for specification purposes. Spectrum shapes and noise characteristics can vary widely for background noises with identical A-weighted sound levels.