Introduction

Sound levels in real environments rarely remain constant. Passing vehicles, machinery starting and stopping, cyclic production processes and human activity can all cause noise levels to fluctuate continuously. A single sound level reading therefore cannot always represent the overall acoustic conditions during a measurement period.

An integrating sound level meter continuously measures sound over a defined period and integrates sound energy over time. Instruments with integrating-averaging capability can also calculate parameters such as equivalent continuous sound level, or Leq, providing a representative value for the total sound energy measured during that period.

In professional acoustics, a distinction is made between an integrating-averaging sound level meter and an integrating sound level meter. The former measures time-averaged, frequency-weighted sound levels, while the latter may be used to determine frequency-weighted sound exposure levels. IEC 61672-1 defines these sound level meter functions and performance requirements.

Key Points

● An integrating sound level meter does more than display an instantaneous decibel value; it evaluates accumulated sound energy over a defined measurement period.
● Instruments with integrating-averaging capability typically measure Leq, while some models also provide SEL, Lmax, Lmin, Peak and other acoustic parameters.
● Leq is not the arithmetic average of multiple decibel readings. It is based on averaging sound energy represented by the squared sound pressure.
● Integrating measurements are particularly useful for traffic noise, industrial noise, environmental noise and other fluctuating sound sources.
● An integrating sound level meter and a noise dosimeter are not the same instrument. Their measurement positions, evaluation methods and primary applications differ.
● The presence of an integrating function alone does not determine whether an instrument is suitable for professional measurements. Frequency weighting, measurement range, dynamic range, instrument class and compliance with applicable standards must also be considered.

What Is an Integrating Sound Level Meter?

An integrating sound level meter is an acoustic measuring instrument capable of continuously acquiring sound pressure signals over a specified period and integrating or averaging the frequency-weighted acoustic energy.

A basic sound level meter is commonly used to observe the current sound level, for example 72.5 dBA at a particular moment. FAST and SLOW time weightings affect how quickly the displayed value responds to changes in sound level, but the reading still primarily represents current or short-term acoustic conditions.

Integrating measurements evaluate the complete measurement period.

For example, during a 30-minute roadside measurement:

● Background levels may remain around 60–65 dBA for much of the time;
● Passing cars may increase the level to 70–75 dBA;
● Heavy vehicles may briefly produce levels above 80 dBA;
● Quieter intervals may return to significantly lower levels.

A single instantaneous reading cannot adequately describe the overall 30-minute noise environment. An integrating sound level meter incorporates changes in acoustic energy throughout the entire period and produces a more representative result.

How Does an Integrating Sound Level Meter Work?

Sound first reaches the microphone, which converts variations in acoustic pressure into an electrical signal. The signal is then processed through stages such as preamplification, frequency weighting, analogue-to-digital conversion and digital signal processing.

During an integrating measurement, the instrument continuously processes the acoustic signal and accumulates the squared sound pressure, which is related to sound energy, over time.

For the commonly used A-weighted equivalent continuous sound level LAeq,T:

$$
L_{Aeq,T}=10\log_{10}\left[\frac{1}{T}\int_{0}^{T}\frac{p_A^2(t)}{p_0^2},dt\right]
$$

where:

● (T) is the total measurement duration;
● (p_A(t)) is the instantaneous A-weighted sound pressure;
● (p_0) is the reference sound pressure;
● (L_{Aeq,T}) is the equivalent continuous A-weighted sound level over period T.

The calculation therefore does not simply add displayed values such as 60 dB, 70 dB and 80 dB and divide by the number of readings.

Because the decibel scale is logarithmic, sound energy must first be averaged correctly before the result is converted back into decibels.

What Is Leq?

Leq stands for Equivalent Continuous Sound Level.

It represents the constant sound level that would contain the same acoustic energy as the actual fluctuating sound over the same measurement period.

For example, the noise from a machine may vary between 65 and 85 dB during a 10-minute operating cycle. The Leq measured over those 10 minutes represents the overall acoustic energy of that complete period with a single value.

Leq is therefore particularly useful for evaluating fluctuating noise.

It is important to understand that Leq is an energy-average quantity rather than a simple arithmetic average of displayed decibel values.

What Is SEL?

SEL stands for Sound Exposure Level.

Unlike Leq, which describes an average over a measurement period, SEL focuses on the total acoustic energy contained in a single sound event.

Typical applications include:

● A train passing a measurement point;
● An aircraft take-off or landing;
● A single stamping-machine cycle;
● One vehicle pass-by;
● A short period of machine operation.

SEL enables sound events of different durations to be compared using a standardized reference duration. It is therefore widely used in transportation, aircraft and event-based noise analysis.

IEC 61672-1 distinguishes between integrating-averaging measurements used for time-average sound levels and integrating measurements used for sound exposure levels.

What Parameters Can an Integrating Sound Level Meter Measure?

Available functions vary between models. Professional instruments may provide several acoustic parameters.

● Leq: Equivalent continuous sound level over the measurement period and one of the principal parameters used in integrating measurements.
● LAeq: Equivalent continuous sound level measured using A frequency weighting.
● LCeq: Equivalent continuous sound level measured using C frequency weighting.
● SEL: Sound exposure level representing the accumulated acoustic energy of a sound event.
● Lmax: Maximum sound level recorded during the measurement.
● Lmin: Minimum sound level recorded during the measurement.
● Peak: Peak sound pressure level, useful when evaluating impulsive sound.
● Statistical levels: Some professional instruments can calculate parameters such as L10, L50 and L90 to characterize the percentage of time during which specified sound levels are exceeded.

The exact parameters available must always be confirmed from the instrument specifications. An instrument described as “integrating” does not necessarily support every parameter listed above.

How Does an Integrating Sound Level Meter Differ from a Conventional Sound Level Meter?

The principal difference is whether the instrument can evaluate accumulated sound energy over time.

A conventional sound level meter is suitable for observing real-time sound levels, for example:

● Checking the current ambient level in dBA;
● Measuring the level when a machine is operating;
● Identifying sudden increases in noise;
● Comparing real-time sound levels between measurement locations.

An integrating sound level meter is better suited to questions such as:

● What was the overall noise level during the last 15 minutes?
● What was the equivalent continuous level of traffic noise over one hour?
● What was the average acoustic energy during a complete production cycle?
● How much sound exposure was produced by one aircraft pass-by?
● What was the overall level of fluctuating noise during the measurement period?

The distinction is therefore based on the measurement objective and data processing method rather than simply on one instrument being “more advanced” than another.

What Is the Difference Between FAST, SLOW and Integration?

These concepts are frequently confused.

FAST and SLOW are time weightings that determine how quickly the displayed sound level responds to changes in the acoustic signal.

FAST responds more rapidly and is useful for observing rapidly changing sound. SLOW responds more gradually and produces a steadier display when the sound level fluctuates significantly.

Integration, however, evaluates acoustic energy over the complete measurement duration.

Therefore:

● FAST is not equivalent to short-term integration;
● SLOW is not equivalent to long-term averaging;
● Leq is not the arithmetic average of readings observed in SLOW mode.

For integrating-averaging measurements, Leq is fundamentally based on energy integration over the complete measurement interval rather than on the FAST or SLOW display response.

What Are the Advantages of an Integrating Sound Level Meter?

For a stable sound source, an instantaneous reading and a time-averaged result may be relatively similar. For fluctuating noise, however, integrating measurement provides significant advantages.

● Evaluation of fluctuating noise: The result reflects the complete measurement period rather than a single point in time.
● More representative results: Leq converts complex sound-level variations into a meaningful overall indicator.
● Suitable for extended measurements: Measurements can extend from minutes to hours or longer, depending on instrument capability.
● Useful for operating-condition comparisons: Leq can be used to compare machines, locations or operating periods under consistent measurement conditions.
● Suitable for environmental noise: Traffic, industrial and construction noise typically vary substantially over time.
● Evaluation of complete sound events: Instruments supporting SEL can assess the accumulated acoustic energy of individual noise events.

Where Are Integrating Sound Level Meters Used?

Integrating sound level meters are particularly useful when sound levels vary over time and an overall assessment is required.

● Industrial environments: Machinery, fans, compressors, stamping equipment and complete production lines.
● Environmental noise monitoring: Road traffic, industrial areas, commercial areas and other environmental sound sources.
● Construction sites: Construction machinery, vehicles and different phases of site activity.
● Transportation noise: Road vehicles, railway traffic and other transportation sources.
● Equipment noise evaluation: Comparison of Leq under different operating conditions.
● Occupational noise surveys: Integrating parameters can provide important information for workplace noise assessment, although occupational exposure evaluations must follow the applicable measurement method and exposure criteria.

Is an Integrating Sound Level Meter the Same as a Noise Dosimeter?

No.

An integrating sound level meter is generally positioned or handheld at a defined measurement location to evaluate the acoustic conditions at that point over a specified period.

A noise dosimeter is designed primarily for personal noise exposure measurements. It is normally worn by a worker, with the microphone positioned near the hearing zone, and records the noise exposure experienced by that person throughout the work period.

Parameters such as TWA and Noise Dose may also depend on defined exchange rates, threshold levels, reference durations and other criteria. Leq should therefore not automatically be treated as equivalent to occupational noise dose or TWA.

A simple distinction is:

● An integrating sound level meter primarily answers: “What was the noise level at this location during this period?”
● A noise dosimeter primarily answers: “How much noise was this person exposed to during the work period?”

What Should Be Considered When Using an Integrating Sound Level Meter?

Integration improves the representativeness of fluctuating-noise measurements, but the measurement method still has a major influence on the result.

● Select a representative measurement duration: The measurement should cover relevant operating cycles or environmental variations.
● Choose the appropriate frequency weighting: A weighting is commonly used for many noise assessments, but the correct weighting depends on the measurement objective.
● Maintain consistent microphone positioning: Position, height and orientation should remain consistent when comparing measurements.
● Avoid operator interference: The operator's body, speech and temporary sound sources can influence the result.
● Control wind-induced noise: Outdoor measurements may require a suitable windscreen.
● Avoid overload: Measurements exceeding the instrument range may invalidate the integrated result.
● Check calibration: For professional measurements, the instrument can be checked with an acoustic calibrator before and after measurement and calibrated at appropriate intervals.
● Record measurement conditions: Measurement time, location, weighting, operating condition, weather and other relevant factors should be documented.

How to Choose an Integrating Sound Level Meter

If the objective extends beyond observing the current decibel level and includes environmental, industrial or long-duration noise analysis, it is important to confirm that the instrument provides genuine integrating measurement functions.

Key specifications include:

● Support for Leq;
● Support for SEL;
● Available frequency weightings such as A, C and Z;
● Measurement and dynamic ranges suitable for the intended sound source;
● Lmax, Lmin and Peak functions;
● Data logging capability;
● Maximum recording duration and memory capacity;
● PC or mobile-device connectivity and data export;
● Class 1 or Class 2 performance and compliance with applicable sound level meter standards;
● Acoustic calibration capability and clear measurement-status indications.

IEC 61672-1 defines Class 1 and Class 2 sound level meters, with different tolerance requirements. For engineering measurements, official reporting or regulatory applications, the appropriate class should be selected according to the requirements of the specific project.

FAQ

Is an integrating sound level meter simply a conventional sound level meter with an averaging function?

Not exactly. True integrating measurement continuously processes the sound pressure signal and performs energy-based integration over time. It is not simply an arithmetic average of several displayed decibel values.

Is Leq an average decibel value?

Leq may be described as an equivalent average noise level over a defined period, but it is not a simple arithmetic average. It is calculated from acoustic energy based on squared sound pressure.

Does Leq always increase when the measurement period becomes longer?

No. If the additional measurement period is relatively quiet, the final Leq may decrease. If significant high-level noise events occur, it may increase.

Can FAST or SLOW replace integration?

No. FAST and SLOW are time weightings that control the response of the displayed level. Integration evaluates sound energy over the entire measurement period.

Can an integrating sound level meter also measure instantaneous sound levels?

Usually yes. Many professional instruments provide conventional sound level measurements together with maximum, minimum, peak and integrating functions. Actual capabilities depend on the model.

Does every integrating sound level meter measure SEL?

No. Some instruments provide only Leq and other integrating-averaging parameters, while more comprehensive instruments may also provide SEL.

Can an integrating sound level meter replace a noise dosimeter?

Not directly. Integrating sound level meters are normally used for measurements at specified locations, while noise dosimeters are typically worn by individuals to evaluate personal occupational noise exposure.

Conclusion

The main purpose of an integrating sound level meter is to extend noise measurement from “how many decibels are present at this moment?” to “how much acoustic energy occurred during the complete measurement period?”

By continuously integrating and averaging the acoustic signal, the instrument can provide parameters such as Leq that represent an entire measurement period. Instruments with additional integrating capabilities may also provide SEL for sound exposure assessment.

For traffic noise, industrial equipment, environmental monitoring and other fluctuating-noise applications, integrating measurements generally provide a more representative result than individual instantaneous readings.

However, “integrating sound level meter” is a broad product description. For professional applications, users should confirm whether the instrument measures time-average sound level, sound exposure level or both, and should also consider measurement range, frequency weighting, instrument class, data-logging capability and the specific measurement objective.