Background noise should not impair oral communication between any two points in the main operating area of the control room.
Additional Information: Figure 12.5 shows the voice levels needed for oral communication over specified distances in the presence of different levels of background noise. Intelligibility of oral communication in noise is affected by the frequency spectra of the noise and of the speakers’ voices and by the speakers’ hearing sensitivity. The decibel on the A-weighted scale (dB(A)) metric employed to measure room noise in these examples should be used as the primary criterion for determining noise conformance. However, the dB(A) metric has certain limitations. If the dB(A) metric proves to be inadequate, for certain types of control room noise environments, especially as regards HVAC noise, the more comprehensive noise criteria (NC) rating method should be used. The NC method uses octave band sound spectra to account for unusual sound spectrum shapes and relates the measured spectra to modified equal-loudness contours whose shapes are level sensitive. The NC rating metric is extensively used in architectural acoustics. In work areas where good voice communications and habitability are required, the octave-band sound pressure levels (SPLs) of continuous noise (not including impulse noise) should be limited to the values given by the NC-50 curve. ANSI/ASA S12.2 (2008) contains more information on the NC rating method.
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Figure 12.5 Oral Communication Level As A Function Of Distance And Ambient Noise Level