A sound level meter (SLM) is a hand-held device that measures sound pressure levels by converting them from Pascals to decibels (dB), with applications in occupational noise monitoring, environmental noise assessment, and building acoustics. Classified into Class 1 and Class 2 based on accuracy, SLMs require calibration to ensure precise and reliable measurements for regulatory compliance.
A sound level meter (SLM), also known as a sound pressure level meter, is a hand-held device designed for precise sound measurements. It consists of a microphone with a windscreen, a preamplifier, a signal processor, and a display. SLM measures the sound pressure level (SPL) in Pascals and converts it into decibels (dB).
The main goal of using sound level meters is to ensure regulatory compliance, protect hearing, monitor noise pollution, and optimize sound quality. These measurements are essential for identifying hazardous noise levels, ensuring safe work environments, and complying with noise level guidelines.
A sound level meter detects air pressure changes caused by sound waves moving its microphone membrane. These mechanical movements are converted into analog electrical signals, which are then amplified and converted to digital signals by the meter’s analog-to-digital (A/D) converter. The result is digital data displayed in decibels (dB) and can be stored for further analysis. This allows the sound meter to measure instantaneous sound levels (SPL, Peak), as well as continuous or equivalent continuous sound levels (Leq).
The sound level meter microphone converts sound waves into electrical signals. Professional measurement microphones meet IEC 61094 standards, ensuring accuracy and wide frequency response. To protect the microphone from dust and water, windscreens are used, maintaining the integrity and precision of the measurements in various environmental conditions.
A sound level meter preamplifier amplifies the signals from the microphone to a level suitable for processing by the signal processor. This amplification is necessary for accurate noise measurement and ensures that the signal can be properly analyzed for various noise metrics, including time and frequency weightings.
The display on a sound level meter provides real-time information about noise levels, showing sound pressure levels in decibels (dB) and frequency analysis in Hertz (Hz). This visual representation allows for immediate assessment and analysis of noise levels, facilitating quick decision-making in environments where noise can vary rapidly.
A sound level meter functions as a data logger by continuously recording noise levels in the form of time history data, spectrograms, and WAV files in consecutive intervals as a logger file. It stores these measurements digitally, allowing for later analysis. This capability is essential for ensuring compliance with noise regulations and identifying trends or patterns in noise exposure, making it valuable for long-term monitoring in various environments.
IEC 61672 sound level meter classes (Class 1 and Class 2) are designations for professional meters, indicating their accuracy and precision. These classes inform users about the device’s decibel accuracy and frequency precision, as defined by the IEC 61672-1 standard. Class 1 meters offer higher accuracy and a wider frequency response range, making them suitable for detailed and precise acoustic measurements, while Class 2 meters are generally used for basic noise assessments.
Class 1 sound level meters offer higher accuracy, a wider frequency response, and a broader temperature operating range than Class 2 meters. For instance, at 1 kHz, Class 1 meters have an accuracy of +/- 0.7 dB, while Class 2 meters have an accuracy of +/- 1 dB. Class 1 meters are suitable for precise acoustic measurements, while Class 2 meters are typically used for general noise assessments.
A sound level meter’s linear operating range is the minimum to maximum sound pressure levels in decibels within the declared frequency range (Class 1 or Class 2) where the device maintains IEC 61672-1 accuracy. According to IEC 61672 standards, digital sound level meters must have at least a 60 dB dynamic range between the lowest and highest measurable dB levels.
The sound level meter frequency range is the minimum to maximum frequencies it can accurately measure within. This range is declared as the middle frequency of 1/3 octave bands. For Class 1 meters, the required range is from 16 Hz to 16 kHz, while for Class 2 meters, it ranges from 20 Hz to 8 kHz. This range ensures that the device can capture a broad spectrum of sound frequencies accurately, meeting the requirements specified by IEC 61672 standards.
The signal-to-noise ratio (SNR) of a sound level meter indicates the margin between the device’s acoustical self-noise and the minimum linear operating range. A higher SNR means the meter can accurately measure low noise levels without interference from its own noise. IEC 61672-1 requires a margin of 7 dBA at 1 kHz for precise sound measurement.
The main sound level meter measurements include:
Sound level meter frequency weightings (A-weighting, C-weighting, and Z-weighting) are digital filters applied to sound according to IEC 61672 standards. These weightings apply frequency corrections in consecutive 1/3 octave bands and are visually represented as frequency weighting curves. Each curve reflects different aspects of human auditory perception:
Sound level meter time weightings (Fast, Slow, Impulse) are digital adjustments applied in exponential averaging to fluctuating noise levels.
A sound level meter measures sound pressure in decibels to simplify the measurement of sound pressures, which range from 0.00002 Pascals (20 micropascals) to 200 Pascals for human hearing. This range corresponds to approximately 0 dB to 140 dB on the decibel scale. The decibel scale logarithmically represents this wide range, making it more manageable. One Pascal equals a sound pressure level of 94 dB, providing a direct correlation between sound pressure and decibel levels. This correlation is essential for precise acoustic measurements, allowing for accurate assessment and management of noise exposure.
Yes, a sound level meter calculates the root mean square (RMS) value, which is an energy measure that refers to the average value of samples of an electrical signal representing sound waves measured by the SLM. When expressed in decibels with frequency weighting, the RMS value is known as the equivalent continuous sound level (Leq).
A sound level meter performs frequency analysis by dividing the measured signal into frequency bands. For occupational noise, 1/1 octave frequency analysis is used, while 1/3 octave analysis is utilized for environmental and building acoustics. FFT narrow band analysis assesses tonality in environmental noise, providing detailed insights into specific noise sources.
Professional sound level meters types include:
A sound level meter is referred to as a noise level meter when it is used to measure unwanted sounds and compare them to established limits. This term emphasizes its application in identifying and controlling noise pollution.
Sound level meters are typically hand-held or mounted on a tripod to provide noise measurements at specific locations. Personal noise dosimeters are worn to assess noise exposure for individuals moving in various environments with different background noise levels.
A noise monitoring station consists of a sound level meter, data transmission modem, and internal battery housed in a weather-protected enclosure. It is designed for long-term, continuous measurement of environmental noise, providing real-time data for regulatory compliance and noise management.
Professional sound level meters’ accuracy is traceable through IEC 61672-3 calibration certificates and IEC 61672-2 pattern approvals. In contrast, noise meter apps on mobile devices lack traceability for their accuracy, making their precision untraceable. Therefore, they are not suitable for the precise measurements required for regulatory compliance.
Professional sound level meter applications include:
An integrating sound level meter is used in noise measurement according to the methodology described by application standards. These standards ensure precise and standardized measurements across different settings.
Sound level meter calibration is the process of adjusting a sound level meter to match a known reference source, ensuring that its readings are accurate and reliable. This is often done using a sound calibrator, which produces a sound at a specific frequency and amplitude for this purpose. Acoustic calibration is required by application standards to ensure that the sound level meter provides precise measurements.
Periodic testing of sound level meters is the accuracy verification procedure, performed every two years at an ISO/IEC 17025 laboratory. Testing by IEC 61672-3 verifies that the meter continues to meet the required standards, maintaining its reliability for noise measurements.
Sound level meter pattern approval is the validation of the device’s accuracy according to IEC 61672-2, verifying conformance to mandatory specifications given in IEC 61672-1. This approval is performed by official measurement bodies to ensure the sound level meter meets international standards for precision and reliability.
To choose the right sound level meter, it is essential to know the relevant application standards (e.g., ISO, OSHA), as they indicate the required IEC/ANSI accuracy class and operating ranges in decibels and Hertz. Ensuring that the meter has a traceable calibration certificate is crucial for accuracy and reliability.
Identify Application Standards: Determine the specific standards your application must comply with, such as ISO or OSHA. These standards will guide you on the required accuracy class (Class 1 or Class 2) and the necessary operating ranges for decibels and frequency.
Check Calibration Certificates: Ensure the sound level meter comes with a traceable calibration certificate. This guarantees that the device has been calibrated against known reference standards and can provide accurate and reliable measurements.
Evaluate Key Features: Consider other important features such as data logging, frequency analysis, time-weighting options (Fast, Slow, Impulse), and connectivity options (USB, Bluetooth) for transferring data to other devices.
Software Support: Look for sound level meters that offer robust software support for data analysis and reporting. This can enhance the usability and functionality of the meter, making it easier to comply with reporting requirements and analyze noise data effectively.
For more detailed information, refer to a comprehensive Sound Level Meter Buyers Guide to understand all the criteria you should consider, including specific features and software support options. This will help you make an informed decision tailored to your specific needs and ensure compliance with relevant standards.
Definition: A sound level meter (SLM) is a hand-held device that measures sound pressure levels by converting them from Pascals to decibels (dB).
Operation: The sound level meter’s microphone converts sound waves into electrical signals, which are amplified and digitized to measure instantaneous and continuous sound levels, displayed in decibels (dB).
Classes: Sound level meters are classified into Class 1 and Class 2 based on accuracy and precision. Class 1 meters provide higher accuracy and a wider frequency response range, suitable for detailed acoustic measurements.
Measurements: Sound level meters measure sound pressure levels (SPL), equivalent continuous sound levels (Leq), peak sound levels (LCpeak), noise exposure (DOSE or LEX, 8h), sound exposure level (SEL), and reverberation time.
Applications: Sound level meters are used for occupational noise monitoring, environmental noise assessment, building acoustics, speech intelligibility (STIPA), sound power and intensity measurements, tonality, and loudness assessments.
Calibration: Sound level meter calibration involves adjusting the device to match a known reference source using a sound calibrator, ensuring accurate and reliable measurements necessary for regulatory compliance.
Professional Use: Sound level meters are essential for ensuring regulatory compliance, protecting hearing, monitoring noise pollution, and optimizing sound quality across various environments and industries.
