A sound level meter is an instrument used to measure sound pressure levels in decibels. It is also commonly referred to as a decibel meter, noise level meter or sound meter.
Sound level meters are used to assess environmental noise, workplace exposure, machinery noise, construction activity, traffic, entertainment venues and many other sources of sound. The instrument converts acoustic pressure into an electrical signal and processes it to produce a measurable sound level reading.
Accurate sound measurement requires more than simply switching on a meter and reading the displayed value. The selected instrument, measurement settings, microphone position, environmental conditions and calibration procedure can all influence the results.
This guide explains how sound level meters work, the most important measurement terms, the differences between instrument classes and the factors to consider when selecting a meter.
What Does a Sound Level Meter Measure?
A sound level meter measures sound pressure level, normally expressed in decibels, or dB.
Sound pressure is the variation in air pressure created by a sound wave. Because the human ear can detect an extremely wide range of sound pressures, sound levels are represented using a logarithmic decibel scale rather than a simple linear scale.
An increase of 10 dB represents a tenfold increase in sound intensity. However, the way people perceive changes in loudness is more complex and depends on factors including frequency, duration and the characteristics of the sound.
Why Are Sound Level Measurements Important?
Noise measurements provide objective information that can be used to evaluate exposure, investigate complaints, identify noise sources and assess whether control measures are effective.
Common reasons for measuring sound include:
- Assessing employee exposure to workplace noise
- Monitoring noise from machinery and industrial processes
- Evaluating environmental noise from roads, railways and airports
- Measuring noise from construction sites
- Investigating residential or commercial noise complaints
- Monitoring sound levels at events and entertainment venues
- Comparing noise levels before and after control measures
- Supporting acoustic research and product development
In Great Britain, the Control of Noise at Work Regulations 2005 require employers to assess and reduce risks caused by workplace noise exposure. The Health and Safety Executive identifies daily or weekly exposure action values of 80 dB(A) and 85 dB(A), with increased control requirements at the higher value.
How Does a Sound Level Meter Work?
A sound level meter receives sound through a microphone and converts it into an electrical signal. The signal is then amplified, filtered, processed and displayed as a sound level measurement.
The main stages of the measurement process are described below.
1. The Microphone Detects Sound Pressure
The microphone is the first and one of the most important components of a sound level meter. It responds to changes in air pressure caused by sound waves and converts them into an electrical signal.
Measurement-grade sound level meters commonly use condenser microphones because of their stability, sensitivity and predictable frequency response.
The microphone must be positioned correctly during a measurement. Reflections from nearby surfaces, wind, incorrect orientation and the operator's body can all influence the result.
2. The Preamplifier Strengthens the Signal
The electrical signal produced by the microphone is very small. A preamplifier strengthens the signal so it can be processed accurately by the instrument without introducing excessive distortion or noise.
3. Frequency Weighting Is Applied
The instrument applies a frequency-weighting filter according to the selected measurement purpose.
The most common frequency weightings are:
- A-weighting, dB(A): Commonly used for environmental noise and average occupational noise measurements because it approximates the sensitivity of human hearing at moderate sound levels.
- C-weighting, dB(C): Provides a flatter response across a wider frequency range and is often used for measuring peak, impact or high-level noise.
- Z-weighting, dB(Z): Provides an almost flat frequency response within the instrument's specified range, with minimal frequency weighting.
The Health and Safety Executive describes A-weighting as commonly used for average noise levels and C-weighting for peak, impact or explosive noises.
4. Time Weighting Is Applied
Time weighting controls how quickly the displayed reading responds to changes in sound level.
Common settings include:
- Fast: Responds quickly to changing sound levels and is useful for observing variations.
- Slow: Produces a steadier reading by responding more gradually.
- Impulse: Used by certain instruments and measurement procedures for short-duration impulsive sounds.
The correct setting depends on the type of sound being measured and the applicable procedure or standard.
5. The Signal Is Processed and Displayed
After weighting and processing, the instrument displays the measurement in decibels.
Depending on the meter, the display may show:
- Current sound pressure level
- Maximum sound level
- Minimum sound level
- Peak sound pressure level
- Equivalent continuous sound level
- Sound exposure level
- Measurement duration
- Frequency-weighting and time-weighting settings
More advanced sound level meters can store measurements, calculate statistics and transfer data to analysis software.
Understanding Important Sound Measurement Terms
Decibel meters may display several different values. Understanding these measurements is essential when interpreting results.
Decibel
The decibel is a logarithmic unit used to express the relationship between a measured sound pressure and a reference sound pressure.
A decibel reading must be interpreted together with the measurement settings, including frequency weighting, time weighting and measurement duration.
Equivalent Continuous Sound Level
The equivalent continuous sound level, commonly written as Leq, represents the constant sound level that would contain the same acoustic energy as a varying sound during a specified measurement period.
When A-weighting is applied, the value is commonly written as LAeq.
Leq is useful for evaluating fluctuating noise from sources such as traffic, machinery and construction activity.
Maximum Sound Level
The maximum sound level is the highest time-weighted sound level recorded during the measurement period.
It should not be confused with peak sound pressure, which measures the highest instantaneous sound pressure.
Peak Sound Pressure Level
Peak sound pressure level represents the highest instantaneous pressure reached by a sound wave.
It is particularly relevant when measuring impact, explosive or impulsive noise. C-weighting is commonly used for peak measurements.
Sound Exposure Level
Sound exposure level, commonly written as SEL or LE, represents the total acoustic energy of an event normalised to a reference duration of one second.
It is useful when comparing separate noise events of different durations.
Statistical Noise Levels
Statistical measurements describe the percentage of time that a particular sound level was exceeded.
Examples include:
- L10: The sound level exceeded for 10% of the measurement period
- L50: The sound level exceeded for 50% of the measurement period
- L90: The sound level exceeded for 90% of the measurement period
L90 is frequently used as an indication of background sound level, although its appropriate use depends on the measurement method and assessment requirements.
Class 1 and Class 2 Sound Level Meters
IEC 61672 specifies two performance classes for sound level meters: Class 1 and Class 2.
Both classes can provide reliable measurements when used for appropriate applications, but Class 1 instruments are subject to tighter acceptance limits and generally provide a wider operating frequency range.
Class 1 Sound Level Meters
Class 1 meters are typically selected for applications requiring higher precision or compliance with measurement procedures that specifically require Class 1 performance.
Common applications include:
- Detailed environmental noise assessments
- Acoustic consultancy
- Laboratory measurements
- Product noise testing
- Regulatory and legal measurements
- Research applications
- Measurements involving a broad frequency range
Class 2 Sound Level Meters
Class 2 meters are commonly used for general-purpose noise surveys and applications where Class 1 performance is not required.
Common applications include:
- Preliminary workplace noise checks
- General industrial measurements
- Educational measurements
- Basic environmental noise surveys
- Routine machinery comparisons
IEC 61672 specifies both Class 1 and Class 2 instruments. The acceptance limits permitted for Class 2 are greater than or equal to those permitted for Class 1.
The required class should be selected according to the measurement objective, applicable regulation, required accuracy and reporting requirements.
Important Sound Level Meter Standards
Several international standards are relevant to sound level measurement.
IEC 61672
IEC 61672 defines performance specifications and testing procedures for sound level meters.
The standard includes:
- IEC 61672-1: Performance specifications
- IEC 61672-2: Pattern evaluation tests
- IEC 61672-3: Periodic testing procedures
IEC 61672 covers Class 1 and Class 2 sound level meters intended to measure sounds generally within the range of human hearing.
ISO 1996
The ISO 1996 series addresses the description, measurement and assessment of environmental noise.
ISO 1996-1 defines basic quantities and assessment procedures, while ISO 1996-2 describes how sound pressure levels used for environmental noise assessment can be determined.
The applicable standard or regulation should always be confirmed before conducting a formal measurement.
Sound Level Meter Calibration
Calibration helps confirm that the sound level meter is responding correctly.
Before measurements, a portable acoustic calibrator is normally fitted over the microphone. The calibrator produces a known sound pressure level at a specified frequency. The displayed reading is checked against the expected value.
A field calibration check should normally be performed before and after a measurement session. A significant difference between the checks may indicate a problem with the instrument, microphone, calibrator or measurement procedure.
Field calibration checks do not replace periodic laboratory testing. IEC 61672-3 describes procedures for periodic testing of sound level meters designed to conform to Class 1 or Class 2 requirements.
session. A significant difference between the checks may indicate a problem with the instrument, microphone, calibrator or measurement procedure.
Field calibration checks do not replace periodic laboratory testing. IEC 61672-3 describes procedures for periodic testing of sound level meters designed to conform to Class 1 or Class 2 requirements.
Calibration and testing records should be retained when measurements are used for compliance, professional reports or quality systems.
Octave and One-Third-Octave Band Analysis
A single overall decibel value does not show which frequencies contribute most strongly to the measured noise.
Octave-band and one-third-octave-band analysis divide the sound spectrum into frequency bands. This helps identify dominant frequencies and can support decisions about noise-control measures, acoustic treatments and hearing protection.
Octave-band analysis is useful for:
- Identifying tonal or frequency-specific noise
- Evaluating machinery noise
- Selecting noise-control materials
- Assessing heating, ventilation and air-conditioning systems
- Supporting environmental and occupational noise investigations
Not every sound level meter includes octave-band analysis. This capability should be selected when frequency information is required.
Common Applications of Sound Level Meters
Workplace Noise Assessment
Sound level meters are used to identify noisy tasks, machinery and work areas. Measurements can support risk assessments and help determine whether further exposure assessment or noise-control measures are required.
A sound level meter measures sound at a location. When the objective is to determine an individual worker's accumulated exposure throughout a working period, a personal noise dosimeter may also be required.
Environmental Noise Monitoring
Environmental measurements may assess noise from:
- Road traffic
- Railways
- Aircraft
- Industrial facilities
- Construction activity
- Entertainment venues
- Commercial premises
- Neighbourhood sources
ISO 1996 provides internationally recognised principles for describing, measuring and assessing environmental noise, but it does not itself establish universal noise limits.
Construction Noise
Construction noise can vary significantly as equipment, activities and locations change throughout the day.
Sound level meters can be used to monitor machinery, evaluate site boundaries, investigate complaints and assess the effectiveness of noise-control measures.
Machinery and Product Testing
Manufacturers use sound level meters to compare machinery, monitor production consistency and evaluate product noise emissions.
Measurements must be performed under controlled and documented conditions when results are intended for comparison or formal reporting.
Event and Entertainment Noise
Sound level meters can help monitor sound levels at concerts, festivals, clubs and other entertainment venues.
Appropriate measurement settings, microphone positioning and averaging periods are necessary to produce meaningful results.
How to Choose a Sound Level Meter
The correct sound level meter depends on the intended application and required measurement data.
Determine the Required Instrument Class
Select Class 1 when the applicable standard, client specification or assessment procedure requires tighter tolerances. Class 2 may be suitable for general surveys and routine measurements where Class 1 performance is unnecessary.
Check the Measurement Range
The instrument must be capable of measuring the lowest and highest expected sound levels without falling below its usable range or overloading.
Review Frequency-Weighting Options
A general-purpose meter should normally include A-weighting. C-weighting is important for peak and high-level noise measurements. Z-weighting may be required for detailed acoustic analysis.
Review Time-Weighting Options
Fast and Slow settings are commonly required. Impulse weighting may be needed for particular applications or measurement procedures.
Consider Integrating Measurement Functions
An integrating sound level meter can calculate values such as Leq over a selected period. This is important when measuring varying or intermittent noise.
Consider Data Logging
Data logging is useful for long-term measurements, identifying changes over time and preparing detailed reports.
Review:
- Storage capacity
- Logging interval
- Battery life
- File format
- Software compatibility
- Data transfer options
Consider Frequency Analysis
Select a meter with octave or one-third-octave analysis when the objective includes identifying dominant frequencies or planning noise-control measures.
Check Environmental Suitability
Outdoor and industrial measurements may require:
- A suitable microphone windscreen
- Weather protection
- Long battery life
- Robust construction
- Remote monitoring capability
- Environmental measurement accessories
Confirm Calibration Requirements
The selected meter should be compatible with an appropriate acoustic calibrator. The availability of periodic calibration or testing services should also be considered.
Common Sound Measurement Errors
Reliable measurements require an appropriate instrument and a consistent procedure.
Common errors include:
- Using an unsuitable instrument class
- Measuring too close to reflecting surfaces
- Holding the meter in a way that affects the sound field
- Using incorrect frequency or time weighting
- Measuring outdoors without a suitable windscreen
- Failing to document weather conditions
- Ignoring background noise
- Failing to check calibration
- Using an inappropriate measurement duration
- Comparing results collected under different conditions
The purpose of the measurement should be defined before selecting the instrument settings and measurement locations.
Frequently Asked Questions
What is the difference between a sound meter and a decibel meter?
The terms sound meter, sound level meter and decibel meter are often used to describe the same type of instrument. Sound level meter is generally the more precise technical term.
What does a sound level meter measure?
A sound level meter measures sound pressure level and displays the result in decibels. Depending on the instrument, it may also calculate values such as Leq, maximum level, peak level and sound exposure level.
What is the difference between dB(A) and dB(C)?
dB(A) applies A-frequency weighting, which is commonly used for average environmental and occupational noise measurements. dB(C) applies C-frequency weighting, which retains more low-frequency content and is often used for peak, impact and high-level noise.
Should I choose a Class 1 or Class 2 sound level meter?
The correct choice depends on the applicable standard, required accuracy and intended use. Class 1 instruments have tighter performance tolerances, while Class 2 instruments are commonly used for general-purpose measurements.
Does a sound level meter need to be calibrated?
The meter should be checked using a compatible acoustic calibrator before and after measurement sessions. It may also require periodic laboratory testing or calibration, depending on the application and quality requirements.
Can a sound level meter measure workplace noise exposure?
A sound level meter can measure noise levels in workplace locations and support noise-risk assessments. A personal noise dosimeter may also be required when measuring an individual's accumulated exposure over a working period.
Can a sound level meter be used outdoors?
Yes, but outdoor measurements require suitable positioning, a microphone windscreen and consideration of weather conditions. Long-term outdoor monitoring may require additional weather protection.
Selecting the Correct Sound Level Meter
A reliable sound level measurement depends on selecting an instrument suited to the application and using it with the correct settings and procedure.
Before selecting a sound level meter, consider the required instrument class, measurement range, frequency weightings, time weightings, data-logging capability, frequency-analysis functions and calibration requirements.
For formal workplace, environmental or regulatory assessments, the measurement procedure and instrument should comply with the applicable standards and legal requirements.