[Code of Federal Regulations] [Title 40, Volume 24] [Revised as of July 1, 2006] From the U.S. Government Printing Office via GPO Access [CITE: 40CFR211.207] [Page 181] TITLE 40--PROTECTION OF ENVIRONMENT CHAPTER I--ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) PART 211_PRODUCT NOISE LABELING--Table of Contents Subpart B_Hearing Protective Devices Sec. 211.207 Computation of the noise reduction rating (NRR). Calculate the NRR for hearing protective devices by substituting the average attenuation values and standard deviations for the pertinent protector category for the sample data used in steps 6 and 7 in Figure 2. The values of -.2, 0, 0, 0, -.2, -.8, -3.0 in Step 2 and -16.1, -8.6, -3.2, 0, +1.2, +1.0, -1.1 in Step 4 of Figure 2 represent the standard ``C''- and ``A''-weighting relative response corrections applied to any sound levels at the indicated octave band center frequencies. (NOTE: The manufacturer may label the protector at values lower than indicated by the test results and this computation procedure, e.g. lower NRR from lower attenuation values. (Ref. Sec. 211.211(b).) Figure 2--Computation of the Noise Reduction Rating Octave band center frequency (Hz).................................. 125 250 500 1000 2000 3000 4000 6000 8000 1 Assumed Pink noise (dB).......................................... 100 100 100 100 100 ..... 100 ..... 100 2 ``C'' weighting corrections (dB)................................. -.2 0 0 0 -.2 ..... -.8 ..... -3.0 3 Unprotected ear ``C''-weighted level (dB)........................ 99.8 100 100 100 99.8 ..... 99.2 ..... 97.0 (The seven logarithmically added ``C''-weighted sound pressure levels of Step 3 equal;107.9 dS) 4 ``A''-weighting corrections (dB)................................. -16.1 -8.6 -3.2 0 +1.2 ..... +1.0 ..... -1.1 5 Unprotected ear ``A''-weighted level (step 1-step 4) (dB)......................................................... 6 Average attenuation in dB at frequency........................... 21 22 23 29 41 ..... (43+47)/2=45 ..... (41+36)/2=38.5 7 Standard deviation in dB at frequency............................ 3.7 3.3 3.8 4.7 3.3 ..... (3.3+3.4)=6. ..... (6.1+6.5)=12.6 7 x2 x2 x2 x2 x2 ..... ............ ..... ............... ----------------------------------------- 7.4 6.6 7.6 9.4 6.6 ..... ............ ..... ............... 8 Step 5-(step 6-step 7) develops the 70.3 76.0 81.4 80.4 66.8 ..... 62.7 ..... 73.0 protected ear ``A'' weighted levels (dB).......................... (The seven logarithmically added ``A''-weighted sound pressure levels of Step 8 using this sample data=85.1 dB) 9 NRR=Step 3--Step 8--3 dB*; =107.9 dB--85.1 dB--3 dB*; =19.8 dB (or 20) (Round values ending in .5 to next lower whole number). *Spectral uncertainty (as defined in Sec. 211.203). The value for 3 is constant. Use Logarithmic mathematics to determine the combined value of protected ear levels (Step 8) which is used in Step 9 to exactly derive the NRR; or use the following table as a substitute for logarithmic mathematics to determine the value of Step 8 and thus very closely approximate the NRR. ------------------------------------------------------------------------ Add this level to Difference between any two sound pressure levels being the higher combined (dB) of the two levels (dB) ------------------------------------------------------------------------ 0 to less than 1.5......................................... 3 1.5 to less than 4.5....................................... 2 4.5 to 9................................................... 1 Greater than 9............................................. 0 ------------------------------------------------------------------------