§ 325.79 Application of correction factors.
Wording first on file in the 1996 annual edition, superseded by the 1998 annual edition.
(a) If two correction factors apply to a measurement they are applied cumulatively.
(b) The following examples illustrate the application of correction factors to sound level measurement readings:
(1) Example 1—Highway operations. Assume that a motor vehicle generates a maximum observed sound level reading of 86 dB(A) during a measurement in accordance with the rules in subpart D of this part. Assume also that the distance between the microphone location point and the microphone target point is 60 feet (18.3 m) and that the measurement area of the test site is acoustically “hard.” The corrected sound level generated by the motor vehicle would be 85 dB(A), calculated as follows:
86 dB(A)Uncorrected reading
+1 dB(A)Distance correction factor
−2 dB(A)Ground surface correction factor
—————
85 dB(A)Corrected reading
(2) Example 2—Stationary test. Assume that a motor vehicle generates maximum sound level readings which average 88 dB(A) during a measurement in accordance with the rules in subpart E of this part. Assume also that the distance between the microphone location point and the microphone target point is 35 feet (10.7 m), and that the measurement area of the test site is acoustically “soft.” The corrected sound level generated by the motor vehicle would be 87 dB(A), calculated as follows:
88 dB(A)Uncorrected average of readings
−3 dB(A)Distance correction factor
+2 dB(A)Ground surface correction factor
—————
87 dB(A)Corrected reading
Amendment history
3 distinct wordings on file since Oct. 1, 1996A new entry appears whenever the regulatory words change between government snapshots. Day-precise from the eCFR (2017 onward); before that, one snapshot per annual CFR edition (revised as of October 1). Bracketed citations are the Federal Register history printed with the section.