Equivalent Continuous Sound Level (Leq)
Definition
Leq (Equivalent Continuous Sound Level)
Leq is the constant sound pressure level that would produce the same total acoustic energy as the actual fluctuating sound over the measurement period. Defined by IEC 61672-1:2013, Leq integrates energy logarithmically and is the primary metric for environmental and occupational noise assessment. SonaVyx computes running Leq in real time.
Leq = 10 × log₁₀[(1/T) × ∫₀ᵀ (p(t)/p₀)² dt] dB
How Leq Is Measured
Leq is computed by continuously integrating the squared sound pressure over the measurement period T, dividing by T, and taking the logarithm. SonaVyx accumulates the mean-square pressure in its DSP pipeline and updates the running Leq display every 100 milliseconds. When combined with A-weighting, the result is LAeq — the most commonly used metric in noise regulations and occupational exposure standards.
Practical Example
A construction site produces intermittent noise: 95 dBA during pile driving (2 hours), 78 dBA during general activity (5 hours), and 65 dBA during breaks (1 hour). The LAeq,8h calculates to 90.2 dBA — dominated by the loudest period despite it lasting only 25% of the shift. This demonstrates how Leq reflects the energy-based nature of noise exposure: short loud periods contribute disproportionately to the overall average.
Why Leq Matters
Leq provides a single-number summary of a complex, time-varying noise environment. Because it is energy-averaged, it gives proportionally more weight to louder events — matching how hearing damage accumulates. A brief 100 dBA event contributes the same energy as a sustained 90 dBA exposure of ten times the duration. This property makes Leq the scientifically appropriate metric for assessing both hearing damage risk and subjective noise annoyance.
Notation Conventions
LAeq,T specifies A-weighted Leq over period T. Common notations include LAeq,15min (15-minute average, used in entertainment regulations), LAeq,1h (hourly average, used in environmental assessment), and LAeq,8h (8-hour average, used in occupational exposure). The notation Ldn and Lden add time-of-day penalties and are used for long-term environmental noise mapping per ISO 1996.
Leq vs TWA
OSHA uses TWA (Time-Weighted Average) which is functionally similar to LAeq,8h but uses a 5 dB exchange rate instead of the 3 dB rate inherent in equal-energy Leq. This means OSHA TWA predicts that doubling exposure time at the same level adds 5 dB rather than 3 dB. NIOSH and ISO 9612 use the equal-energy 3 dB exchange rate, which is scientifically more accurate and corresponds directly to Leq.
Sound Exposure Level (SEL)
SEL (also written LAE) normalizes the total energy of a noise event to a 1-second duration. SEL equals the Leq of the event plus 10 × log(T/1s). This allows comparison of events with different durations — a 30-second aircraft flyover and a 2-second door slam can be compared directly through their SEL values. SonaVyx computes SEL alongside Leq for comprehensive event characterization.
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