Document ID: chunk:federal_register_of_legislation:F2024L00089:reg:800:p8
Version: federal_register_of_legislation:F2024L00089
Segment Type: reg
Provision Reference: reg 800 (pt 8/16)
Character Range: 49815–53126

2.3.1. Measurement criteria for A-weighted sound pressure level

              The background, or ambient noise, shall be measured for a duration of at least 10 seconds. A 10 second sample taken from these measurements shall be used to calculate the reported background noise, ensuring the 10 seconds sample selected is representative of the background noise in absence of any transient disturbance. The measurements shall be made with the same microphones and microphone locations used during the test.

              When testing in an indoor facility, the noise emitted by the roller-bench, chassis dynamometer or other test facility equipment, without the vehicle installed or present, inclusive of the noise caused by air handling of the facility and vehicle cooling, shall be reported as the background noise.

              The recorded maximum A-weighted sound pressure level from both microphones during the 10 second sample shall be reported as the background noise, Lbgn, for both left and right microphones.

              For each 10 second sample at each microphone, the maximum to minimum range of the background noise, ∆Lbgn, p-p, shall be reported.

              The one-third-octave frequency spectrum, corresponding to the reported maximum level of background noise in the microphone with the highest background level, shall be reported.

              As an aid for measurement and reporting of background noises see flowchart in Figure 4 of the Appendix to this annex.

              2.3.2. Vehicle A-weighted sound pressure level measurement correction criteria

              Depending on the level and the range of maximum to minimum value of the representative background noise A-weighted sound pressure level over a defined time period, the measured jth test result within a test condition, Ltest,j, shall be corrected according to the table below to obtain the background noise corrected level Ltestcorr,j. Except where noted, Ltestcorr,j = Ltest,j - Lcorr.

              Background noise corrections to measurements are only valid when the range of the maximum to minimum background noise A-weighted sound pressure levels are 2 dB(A) or less.

              In all cases where the range of the maximum to minimum background noise is greater than 2 dB(A), the maximum level of the background noise shall be 10 dB(A) or greater below the level of the measurement. When the maximum to minimum range of background noise is greater than 2 dB(A) and the level of the background noise is less than 10 dB(A) below the measurement, no valid measurement is possible.

       Table 3
Correction for level of background noise when measuring vehicle A-weighted sound pressure level
Correction for background noise
Range of maximum to minimum value of the representative background noise A-weighted sound pressure level over a defined time period   Sound pressure level of j-th test result minus background noise level  Correction in dB(A)
∆Lbgn, p-p in dB(A)                                                                                                                   ∆L = Ltest,j - Lbgn                                                    Lcorr
                                                                                                                                      in dB(A)
-