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Sound Exposure Level

Reference data and engineering information about sound exposure level for acoustics applications.

soundexposurelevel

Overview

Engineering reference data for Sound Exposure Level in acoustics.

Key Formulas

Speed of Sound

c=γRTc = \sqrt{\gamma R T}

Speed of sound in an ideal gas.

Sound Level

L=10log⁡10(I/I0)L = 10 \log_{10}(I/I_0)

Decibel level.

Wavelength

λ=c/f\lambda = c / f

Wavelength = speed / frequency.

Variables

SymbolDescriptionUnit
ccSpeed of soundm/s
LLSound leveldB
λ\lambdaWavelengthm
ffFrequencyHz

Properties and Applications

Sound Exposure Level (Ls) is a specialized metric that characterizes transient or intermittent noise events. Its key properties and uses include:

  • Energy Accumulation: Ls integrates both the magnitude of a sound over time and the duration of that sound, providing a single-number measure of total sound energy for a discrete event.
  • Event-Based Metric: It is ideal for quantifying single noise events such as a passing aircraft, a vehicle overpass, or a train horn blast.
  • Moving Sources: As noted, it is particularly useful for noise from moving sources where the sound level changes over a short period.
  • Relationship to Duration: Two events with the same Ls value have the same total sound energy, even if one is louder but shorter and the other is quieter but longer.

Comparison of EPA Sound Descriptors

The EPA uses a suite of descriptors to assess environmental noise. The table below summarizes the primary ones mentioned.

DescriptorSymbolPrimary Use
A-weighted Sound LevelLAGeneral measurement of sound pressure level, adjusted for human hearing sensitivity.
Sound Exposure LevelLsTotal sound energy of a single, distinct noise event (e.g., a plane flyover).
Equivalent Sound LevelLeqRepresents a constant sound level that has the same total energy as a time-varying sound over a specified period.
Day-Night Sound LevelLdnLong-term environmental metric that applies a 10 dB penalty to nighttime (10 PM - 7 AM) sound levels.

Practical Example

The sound exposure level for a single noise event can be conceptualized as the A-weighted energy of the event normalized to a reference duration of 1 second. If an event's Ls is 85 dB, it means the total acoustic energy of that event is equivalent to a steady 85 dB sound lasting for exactly 1 second.

References

Source: engineeringtoolbox.com