NCJ RENR flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Sound pressure level formula

Lp = 20 log10(p/p0) where p0 = 20 micropascals. Doubling pressure adds about 6 dB; tenfold pressure adds 20 dB.

A-weighting purpose

Frequency weighting that approximates human loudness by reducing low-frequency sensitivity and slightly emphasizing 2–4 kHz; common in community and occupational dBA limits.

Energy averaging Leq

Leq = 10 log10[(1/T) Σ ti 10^(Li/10)]. It is the steady level with the same acoustic energy as the fluctuating measurement over period T.

Ldn versus Lden

Ldn adds 10 dB to night hours before averaging over 24 h; Lden adds 5 dB evening and 10 dB night, used in EU environmental noise assessment.

Point versus line divergence

A point source loses about 6 dB per doubling of distance; an infinite line source such as a roadway loses about 3 dB per doubling.

Type 1 versus Type 2 meters

IEC 61672-1 Type 1 tolerances are tighter (about ±0.7 dB) than Type 2 (about ±1.0 dB); compliance rules may require Type 1.

Field calibration requirement

Calibrate before and after each measurement set at a known level, commonly 94 dB at 1 kHz; drift over 0.5 dB typically invalidates the data set.

Fast and Slow weighting

Fast time weighting uses a 125 ms exponential average for fluctuating noise; Slow uses 1 s for steady sources; choice must match the governing method.

Windscreen function

Reduces wind-induced microphone noise and protects the diaphragm; high wind can still bias low-level readings and may invalidate measurements.

Microphone placement factors

Height above ground, distance from facades, and nearby reflecting surfaces alter measured levels; record exact geometry because reflections can add several dB.

Sampling period selection

Choose day, evening, and night plus weekday and weekend periods that capture the operating cycle and worst-case source activity for the metric required.

Residual background survey

Measurement with the source off, used to characterize existing ambient and, where rules allow, correct the total level to estimate source contribution.

Rejecting extraneous events

Log and exclude periods contaminated by aircraft, sirens, or animals; retain the rejected raw data and reasons to preserve defensibility.

Receptor location definition

The point specified by the permit or standard, such as property line or nearest dwelling facade, at the stated height; record coordinates and geometry.

Measurement uncertainty near limits

When result plus expanded uncertainty spans the limit, report the uncertainty rather than asserting a definitive exceedance or compliance.

OSHA 1910.95 exposure limits

Occupational noise rule: 90 dBA 8-hour permissible exposure limit, 5 dB exchange rate, hearing conservation action level at 85 dBA.

Clean Air Act Title IV

Directs EPA to publish noise criteria and coordinate federal noise research; it does not itself set enforceable community noise limits.

FHWA 23 CFR 772 scope

Governs federal-aid highway noise studies, abatement consideration, and traffic noise prediction requirements for highway projects.

ANSI S12.9 series role

Provides methods for describing and measuring community noise, including metrics, sampling, and assessment procedures referenced by permits and studies.

IEC 61672-1 scope

Specifies electroacoustic performance and tolerance classes for sound level meters, including Type 1 and Type 2 instruments and periodic verification.

Metric matching rule

Compare the measured metric to the same metric in the limit: Lmax to Lmax, Leq to Leq, octave band to octave band.

Background energy subtraction

Source level Ls = 10 log10(10^(Ltot/10) − 10^(Lbg/10)); apply only when the governing rule permits background correction.

Permit limit elements

Each limit specifies metric, averaging time, location, and time window; all elements must be satisfied for compliance.

Exemptions and exceptions

Permits may exempt emergency equipment, construction hours, temporary activities, or grandfathered sources; identify these before concluding noncompliance.

Barrier insertion loss

Depends on path-length difference over the barrier edge, frequency, and geometry; practical attenuation is roughly 10–20 dB.

Atmospheric absorption

Frequency-dependent energy loss during propagation, increasing with distance and humidity; ISO 9613-2 provides engineering coefficients for modeling.

Model validation

Compare predicted levels to field measurements at representative receptors; adjust source emission and local corrections to reduce systematic bias.

Sensitivity analysis

Vary source levels, operating hours, and receptor locations to show how predicted impacts and conclusions change with assumptions.

Chain of custody entries

Each transfer records custodian, date and time, purpose, and signature; unsigned or missing entries weaken evidentiary reliability.

Raw data preservation

Keep original meter files and recordings unaltered, work from copies, and checksum originals to demonstrate integrity.

Contemporaneous field notes

Notes made during sampling in ink or validated electronic form; corrections are struck through and initialed rather than erased.

Report content elements

State purpose, standards cited, instrumentation and calibration, sampling design, results, uncertainty, conclusions, and limitations; separate facts from interpretation.