The difference between Peak noise level (L10) and background noise level (L90) is known as

Question

Accepted Answer

Correct answer: B — Concept — statistical (percentile) noise levels. Environmental noise is not steady, so a site is described by percentile levels LN: the sound level that is exceeded for N% of the measurement period. Two of these are standard. L10 is exceeded only 10% of the time, so it represents the intrusive, near-peak component of the record; L90 is exceeded 90% of the time, so it represents the residual level that persists when the loud events are absent — the background. The decibel spread between an upper and a lower percentile level is itself a named index, used to state how widely the noise at a site fluctuates. Application to this question. Identify the two quantities named in the stem: L10 is the peak (near-maximum) noise level and L90 is the background noise level at the same site, both in dB(A). The quantity asked for is their arithmetic difference, L10 − L90, expressed in decibels. That difference is, by definition, the noise climate (NC) of the site: NC = L10 − L90. Reading the value: a large noise climate means the level swings far above the background (for example a quiet road crossed by occasional heavy vehicles); a small noise climate means a steady, unvarying noise such as continuous plant machinery. Cross-check against the other quantities named. Quantity How it is defined Noise environment Qualitative description of the acoustic setting — the sources present, the propagation paths and the surrounding land use. It is not a decibel statistic computed from a percentile record. Noise climate NC = L10 − L90 (dB) — the spread between the intrusive and the residual percentile levels. Traffic noise index TNI = 4(L10 − L90) + L90 − 30 — it contains the same difference, but weighted four times and combined with the background level and a constant, so it is a different number. Sound energy level LE = 10 log10(E/E0), with E0 = 1 pJ — an absolute level describing the total acoustic energy of an event, not a difference between two levels. Hence the difference between the peak noise level L10 and the background noise level L90 is the noise climate.

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A. Noise environment

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B. Noise climate

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C. Traffic noise index

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D. Sound energy level

Quantity	How it is defined
Noise environment	Qualitative description of the acoustic setting — the sources present, the propagation paths and the surrounding land use. It is not a decibel statistic computed from a percentile record.
Noise climate	NC = L10 − L90 (dB) — the spread between the intrusive and the residual percentile levels.
Traffic noise index	TNI = 4(L10 − L90) + L90 − 30 — it contains the same difference, but weighted four times and combined with the background level and a constant, so it is a different number.
Sound energy level	LE = 10 log10(E/E0), with E0 = 1 pJ — an absolute level describing the total acoustic energy of an event, not a difference between two levels.

The difference between Peak noise level (L10) and background noise level (L90)…