The acoustic environment around computer workstations should allow oral communication and aid concentration.
Additional Information: The maximum ambient noise levels specified in dB(A) under “Background Noise” above should be used as the primary criterion for determining noise conformance around the computer workstation. If the dB(A) metric proves to be inadequate, or if a more in-depth analysis is needed, for certain types of noise environments, especially as regards unbalanced or rumbly sound spectra, the more comprehensive balanced noise criteria (NCB) rating method should be used. The NCB method represents an enhancement of the NC method described above. The NCB method accounts for unbalanced sound spectrum shapes and extends down to 16 hertz (Hz) to include low frequency noise components commonly found in many rooms. It also relates these spectra to speech interference levels (SILs) and corrects for rumbly spectra. The maximum level of background noise emissions from a computer workstation and its components should have an NCB rating ranging between 38 and 43, and strive to achieve an NCB rating as low as possible within this range. These NCB values assume occupied
spaces, with the HVAC system operating and all other sources of normal and interior and exterior noise also operating. Such values do not interfere with oral communication and provide an environment quiet enough to aid concentration on mental tasks. More information on the NCB rating method may be found in ANSI/ASA S12.2 (2008).100