LEQ Equivalent Continuous Sound Level

Leq (Equivalent Continuous Sound Level) is a crucial metric in acoustics and noise studies, representing the average sound level over a designated period. It reflects sound energy and potential hearing damage due to cumulative exposure.

Must know

What is the meaning of Leq in acoustics?

The Leq (Equivalent Continuous Sound Level) is a key metric in acoustics and noise studies, representing the average sound level over a designated period. The term ‘equivalent’ indicates that the combined energy from fluctuating sound levels during a timeframe is equivalent to the energy from a constant, non-varying sound level for that same duration. ‘Continuous’ implies that Leq represents this sound as though it maintained a consistent level throughout the observed period.

What does the Leq result represent?

The Leq result represents the same energy content and hearing damage potential as the varying sound level. Sound energy is crucial when considering potential hearing damage. The human ear responds to the energy in sound, and cumulative exposure over time can result in hearing damage or loss.

What does the Leq result represent

Leq can be used to represent noise in various contexts, such as occupational environments (e.g., factories), recreational settings (e.g., concerts), or urban areas (e.g., traffic noise). It helps policymakers, professionals, and researchers evaluate and compare noise exposures and set permissible limits. The Leq offers a comprehensive way to represent complex noise environments with a single value, making it easier to communicate, understand, and act upon the potential impacts of noise on health, well-being, and other aspects of life.

The advantages of using Leq in measurements include:

  • Leq​ is a globally recognized parameter that summarizes the fluctuating levels of noise over a particular period into an average value. This makes it a convenient tool for communicating the overall noise exposure or environment
  • The A-weighted Leq emphasizes frequencies to which the human ear is most sensitive and de-emphasizes those frequencies where our hearing is less sensitive. This makes LAeq​ particularly relevant for human exposure as it represents the noise in a way that aligns with our perceptual response.
  • LAeq​ provides an average of the entire audible frequency range, which can be crucial for a holistic understanding of the sound environment.
  • Leq can be frequency-weighted (e.g., A, C, or Z weightings) to provide insights into specific frequency contributions, including the influence of low frequencies.
  • Leq integrates varying sound levels over time, providing a consistent representation as a single dB value, which depicts the equivalent continuous sound exposure,
  • Leq serves as a foundational metric from which various other acoustic indicators, like LEX,8h for occupational noise or Rating Level for environmental noise, can be derived.
  • Leq can be represented as a frequency spectrum in 1/1 or 1/3 octaves to assess the annoyance accurately.

What is the Leq formula?

The definition from IEC 61672-1 for the equivalent continuous sound level (Leq) is often expressed mathematically as formula:

LEQ equation formula


  • LAeq is the A-weighted equivalent continuous sound level 
  • pA(t) is the A-weighted sound pressure signal
  • T is the duration of the measurement.
  • p0 reference air pressure is 20μPa (micro Pascals).

In the Leq equation, the term inside the logarithm represents the time average of the square of the sound pressure over the time period T. This average is then compared to the square of the reference pressure (which is squared and thus omitted from the equation for clarity) using a logarithm to convert the ratio to a decibel scale. It’s important to note that the Leq formula is for A-frequency-weighted sound pressure, meaning it accounts for the varying sensitivity of the human ear to different frequencies. 

What is A-weighted Leq?

The A-weighted Leq, commonly represented as LAeq​, means that the Leq is measured with the applied A-weighting. This weighting emphasizes or attenuates certain frequencies in a broadband sound signal to reflect the human ear’s frequency response. Various weightings are used in acoustics to adjust sound measurements to be more representative of human hearing, with A-weighting being the most prevalent. It emphasizes frequencies, particularly between 1 kHz and 4 kHz, to which the human ear is especially sensitive.

frequency curves

What is dB(A) Leq?

The dB(A) Leq refers to the Leq decibels result measured with an “A-weighting” filter applied, which is designed to approximate the frequency response of the human ear at typical conversational levels.

What is the difference between LEQ and SPL?

The Leq (Equivalent Continuous Sound Level) and SPL (Sound Pressure Level) are both metrics used in acoustics to describe the characteristics of sound. The SPL gives the level of sound at a specific moment and can be frequency-weighted (like A, C, or Z weighting) and also time-weighted (Fast, Slow). On the other hand, the Leq is a time-averaged measure of the sound pressure levels over a specified period, which is typically frequency-weighted, but without the Fast or Slow time-weighting used in SPL measurements.

What does it mean that Leq is linear?

The Leq​ is linear means it doesn’t incorporate a time weighting like “slow” or “fast” which are typically used in sound level meters for instantaneous readings. In the IEC 61672-1 standard time weightings such as “slow” and “fast” are used to describe how a sound level meter responds to changes in the instantaneous sound level.


What are Lmax and Lmin?

The Lmax and Lmin are the maximum and minimum time-weighted sound levels that provide crucial information about the variability of noise levels over a specific interval. They help in assessing both the highest and the quietest noise environments, which can be particularly important in contexts like environmental noise studies or occupational noise assessments. Following the guidelines provided by the IEC (International Electrotechnical Commission):

  1. Maximum Time-weighted Sound Level (Lmax​):
    • This represents the highest time-weighted sound level observed during a defined time interval.
    • The subscript “A” typically denotes the application of the A-frequency weighting, which is designed to reflect the frequency response of the human ear.
    • The “F” LAFmax​ stands for ‘Fast’ time weighting, which has a response time of 125 milliseconds. Similarly, the “S” LASmax​ represents ‘Slow’ time weighting, which has a response time of 1 second. The “max” denotes that it’s the maximum value recorded with that time weighting during the measurement period.
  2. Minimum Time-weighted Sound Level (Lmin​):
    • This is the lowest time-weighted sound level recorded during the specified time period.
    • As with the maximum levels, these values can be influenced by the chosen frequency weighting (typically “A” for auditory response) and time weighting (either ‘Fast’ or ‘Slow’).

What is Ldn in noise?

The Ldn in noise is a leq-based Day-Night Average Sound Level. This is a 24-hour Leq average of noise levels but with a 10 dB penalty added to noise levels measured during nighttime hours (typically 10 pm to 7 am) to account for the increased sensitivity to noise during nighttime. It’s often used in environmental noise studies, especially around airports.

What is Lden?

Lden is the Day-Evening-Night Average Sound Level. It’s similar to Ldn but has an additional time period (evening) and typically applies a 5 dB penalty to the evening hours and a 10 dB penalty to the nighttime hours. It’s a metric used in the European Union for assessing environmental noise.

What is the CNEL in noise?

CNEL in noise means Community Noise Equivalent Level used in the United States for environmental noise assessment. It’s similar to Lden in Europe: it considers an evening period with a penalty. Specifically, it’s a 24-hour average noise measure with a 5 dB penalty added for the evening (typically 7 pm to 10 pm) and a 10 dB penalty added for nighttime (10 pm to 7 am).

What is LEX,8h?

The Daily noise exposure level LEX,8h​ is defined by ISO 1999 as the A-weighted equivalent continuous sound level normalized to an 8-hour working day. LEX,8h is frequently used in occupational health and safety regulations to set limits on allowable noise exposure to prevent hearing damage. Daily noise exposure level (LEX,8h) incorporates all types of noise exposures at work, even those that are impulsive in nature. The intent is to capture the entire noise exposure over a standard workday so that even if a worker’s actual exposure varies (e.g., they’re exposed to noise for only 6 hours), the LEX,8h​ reflects what their exposure would be if it was spread out evenly over 8 hours.

What is the LEPD in noise?

The LEPD​ stands for the Daily Personal Noise Exposure. It is a measure used to express the total noise exposure received by an individual over a working day. The term is often associated with noise exposure regulations in the context of occupational health, and it’s used to assess the risk of hearing damage from workplace noise. The term LEX,8h​  later became more widely used, especially in European contexts, to represent the same concept but standardized to an 8-hour workday.

What are Statistical Levels L90, L50, L10?

Statistical levels, denoted as LN, provide an analysis of sound levels over a specified measurement period. They offer insights into various noise parameters, highlighting the quietest, loudest, and median intervals of noise. This information is crucial for determining the intrusiveness of specific noise sources within an environment. The principle behind these statistical levels is rooted in the percentage of time certain sound levels are surpassed:

  • L90: This sound level is exceeded 90% of the measurement time. It is frequently used as an indicator of background or ambient noise levels, sometimes alongside L95.

  • L50: Represents the sound level that is exceeded for 50% of the measurement time. It’s commonly employed in environmental noise studies to depict the median ambient noise level.

  • L10: This is the sound level surpassed only 10% of the time, denoting louder noise events that occur less frequently in the environment.

Notably, sound level meters determine LN statistical levels based on short LEQ results, such as 100 ms intervals. In these instances, LN statistical levels are referred to as Leq Statistics.

LN L90 L10 L50 statistical level

What is Leq Sound Level Meter?

A Leq​ Sound Level Meter is a type of integrating sound measuring instrument designed to measure the average sound pressure level over a specified period of time. Leq sound level meters are used to assess the potential harm of noise to human hearing, especially in occupational and environmental noise assessments, among other applications. A professional Leq sound level has features like frequency weighting (e.g., A-weighting or C-weighting) and selectable Leq integration interval (e.g 1 minute or 1 hour).

leq application

LEQ Equivalent Continuous Sound Level: Key Takeaways

  1. Leq stands for “Equivalent Continuous Sound Level,” a fundamental metric in acoustics and noise studies.
  2. Leq represents the average sound level over a designated period, treating fluctuating sound levels as equivalent energy to a constant sound level.
  3. The Leq result holds the same energy content and potential hearing damage as varying sound levels.
  4. The Leq formula is defined mathematically using sound pressure and time duration, accounting for frequency weighting.
  5. Leq is linear, lacking time weightings like “slow” or “fast” found in sound level meters.
  6. dB(A) Leq refers to Leq measured with an A-weighting filter for typical conversational levels.
  7. Leq and SPL (Sound Pressure Level) are both acoustics metrics; Leq is time-averaged, while SPL is instantaneous.
  8. Lmax and Lmin represent maximum and minimum time-weighted sound levels, useful for assessing noise variability.
  9. Ldn is a leq-based Day-Night Average Sound Level, including a nighttime penalty.
  10. Lden is similar to Ldn, including evening and nighttime penalties, used in the European Union for environmental noise assessment.
  11. CNEL (Community Noise Equivalent Level) in the US and Lden in Europe are similar, considering evening and nighttime penalties.
  12. LEX,8h is the daily noise exposure level normalized to an 8-hour workday, used for hearing damage prevention.
  13. Leq statistical levels (L90, L50, L10) provide insights into quiet, median, and loud periods of noise.
  14. Leq Sound Level Meter measures the average sound pressure level over a specific time, used in noise assessments.

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