The left graph below shows the ambient chamber noise in each 1/3 octave band.  Measurement of chamber noise presents a problem due to the self-noise of a microphone, which often dominates the measurement.  This measurement was obtained by paralleling eight matched microphones, which reduces the microphone noise by 9dB.  Nevertheless the mid and high bands still remain dominated by microphone noise.  The ambient chamber noise is actually below the 2dB SPL values.  As a comparison with the standard SMPTE cinema noise criteria curves shown in Blue, the chamber is well below the lowest NC-15 curve.  The ANSI-A weighted broadband noise for the chamber is 13dB SPL.