A sound level meter measures sound pressure levels in decibels (dB) and comes in various types, including Class 1 and Class 2, each with different levels of accuracy. Calibration is crucial for accuracy, and the choice of the meter depends on specific applications like environmental monitoring and workplace safety.
A sound level meter measures sound pressure levels in decibels (dB). This hand-held instrument consists of a microphone to capture sound, an amplifier to enhance the signal, and a display to indicate the dB level. Advanced versions also have data integration and logging capabilities, which calculate the equivalent continuous sound level (Leq). The device can incorporate time and frequency weightings. Time weighting applies mathematical formulas based on time constants, either “Fast” or “Slow,” to weigh samples. Frequency weightings like A and C apply digital filtering to the signal, attenuating or amplifying it to approximate human hearing sensitivity. Classifications into Class 1 and Class 2 ensure varying degrees of measurement accuracy, making the device versatile for applications like environmental monitoring and workplace safety.
Sound level meter operation consists of conducting sound pressure level measurements to generate indicators such as Leq, SPL, Peak, Max, and Min. The device utilizes a microphone to sample noise at a predetermined rate. A preamplifier adjusts the signal strength, which is then digitized by an A/D converter. This digital signal undergoes processing by the Digital Signal Processor (DSP), starting with frequency weighting. After frequency weighting, the signal either undergoes time weighting or directly moves to linear integration. Integration means the sound level meters calculate average readings over a specific period. Integrated values are calculated into measurement indicators like Leq, SPL, Peak, Max, and Min at specific time intervals. Data is stored in the device’s memory, covering intervals from microseconds to hours or days, for future recall or download. The operational setup includes configuring these features and selecting the appropriate functions for the specific measurement task. The device operates on either internal batteries or an external power source.
Noise level meters are specialized sound level meters designed to measure unwanted sounds and compare them to established limits. These meters often take the form of either noise dosimeters or noise monitoring stations. Noise dosimeters are wearable devices that measure an individual’s noise exposure over a set period, commonly used in occupational health assessments to ensure safe noise levels. Noise monitoring stations are fixed installations designed for long-term, continuous measurement and logging of ambient noise. These stations are frequently used in environmental monitoring projects and have the capability to transmit data remotely for analysis.
Organizations like ISO, IEC, and ANSI all use the term “sound level meter” as their standard name. Professionals in the field tend to use this term. However, non-professionals may use the terms “sound” and “noise” interchangeably and may refer to outdoor noise monitors as “noise meters.” It is important to note that these terms may not accurately describe the device’s capabilities or accuracy.
The terms “type” and “class” in the context of sound level meters refer to different aspects of the device’s design and performance. “Type” generally describes the specific functionalities and applications for which the meter is designed. For example, a noise dosimeter is a type of sound level meter designed for measuring an individual’s exposure to noise over time. On the other hand, “class” refers to the accuracy and precision of the meter, often categorized as Class 1 or Class 2. Class 1 meters offer higher precision and are suitable for scientific research and legal proceedings, while Class 2 meters are generally used for less critical applications like basic industrial noise assessments.
Types of sound level meters vary based on their specialized design, features, and applications. They range from basic decibel meters for quick assessments to advanced noise monitoring stations for long-term environmental studies. Specialized types include audio level meters for audio engineering, SPL meters for high-precision scientific work, and personal noise dosimeters for occupational health. Digital and professional sound level meters offer enhanced accuracy and functionality, while smartphone applications provide convenience but lack precision. Each type is tailored for specific tasks or environments and varies in complexity and accuracy.
A decibel meter, or dB meter, is designed for quick, general assessments of sound levels in decibels (dB). This basic device measures instantaneous sound levels across different settings but typically lacks advanced features like frequency and time weighting. As a result, it is less suitable for specialized measurements. In recent times, mobile apps are increasingly replacing traditional decibel meters.
Sound level meter apps use a phone’s built-in microphone to approximate sound levels. Unlike basic decibel meters, these apps often include frequency and time weighting features due to the processing capabilities of mobile phones. However, their accuracy is compromised because they rely on inbuilt MEMS microphones designed for capturing human speech, and they are not calibrated for precise measurements.
A digital sound level meter uses Analog-to-Digital (A/D) conversion and Digital Signal Processing (DSP) for enhanced accuracy and versatility. It captures sound via a microphone, amplifies the signal through a preamplifier, and then converts this analog signal to a digital format using the A/D converter. The digital signal is processed and displayed on a digital screen in a real-time.
In contrast, analog sound level meters operate without the A/D conversion, presenting measurements through a needle on a dial or other non-digital methods. The inclusion of the A/D converter in digital sound level meters allows for more advanced features, such as data logging, real-time frequency analysis, and easier integration with software applications for further analysis. These digital features make it versatile across a range of applications, including environmental monitoring, occupational safety, and research settings.
An integrating sound level meter is a specialized type of sound level meter that calculates the average sound pressure level over a defined period of time. This feature allows the meter to provide a more comprehensive view of the noise environment, capturing fluctuations and peaks to produce an equivalent continuous sound level, often denoted as Leq. Integrating sound level meters is particularly useful in applications where noise levels vary significantly over time, such as in industrial settings, environmental monitoring, and occupational health assessments.
An SPL meter is designed for high-precision measurements of sound pressure levels in decibels. Unlike basic decibel meters, it comes with settings for frequency and time weightings, making it ideal for scientific research and industrial applications where precise readings are essential.
A Personal Noise Dosimeter is a wearable sound level meter designed for occupational settings to monitor an individual’s noise exposure throughout a workday. These devices are engineered to operate for at least 8 hours, capturing data that helps ensure workers are not exposed to harmful noise levels.
A Noise Monitoring Station is a fixed installation of a sound level meter intended for long-term, continuous measurement and logging of ambient noise levels. These stations are commonly used in environmental monitoring projects and have the capability to transmit data remotely for analysis.
Audio level meters, also known as audio analyzers, serve distinct purposes based on their design and application. Fixed systems are primarily used for quality control in the manufacturing and servicing of audio products like speakers, mobile phones, and earphones. These systems often employ Fast Fourier Transform (FFT) analyses and are usually multichannel.
On the other hand, portable audio analyzers are geared towards automotive and R&D applications, including Noise, Vibration, and Harshness (NVH) studies in vehicles. These portable systems also offer FFT-based real-time analyses, covering metrics such as time signal, FFT, octave, one-third octave, level vs. time, loudness, sharpness, specific loudness, articulation index, and order spectrum.
A voice level meter is specialized for measuring the sound levels of human speech and is commonly used in music and psychoacoustic applications. It offers metrics such as tonality, loudness, octave, and one-third octave. Additionally, it is employed for Speech Transmission Index for Public Address systems (STIPA) to assess the intelligibility of public address systems.
The American National Standards Institute (ANSI) has established Standard S12.60 for Classroom Acoustics. ANSI standard set maximum levels for reverberation time measurements (RT60) and background noise. These maximum levels are applicable in classrooms. To comply with regulations, a classroom noise meter, such as the SV 973 with reverberation time measurements and STIPA options installed, can be used. A professional Class 2 SLM is typically sufficient for classroom use, as it is accurate enough and less expensive than a Class 1 meter.
A professional sound level meter is engineered for high-precision measurements in scientific research and industrial applications. These meters are digital and integrating, offering advanced features like real-time frequency analysis, extensive data logging, and options for audio analysis such as 1/1 and 1/3 octave, WAV recording, as well as loudness, STIPA, or FFT. They are classified according to IEC or ANSI standards, ensuring the highest level of accuracy. There are also specialized sound meters designed for specific applications. For example, Ultrasound or Infrasound band meters that measure noise levels in specific frequency bands. Some noise level meters come with additional features like Octave Band Statistics for more advanced noise analysis.
Several professional brands produce high-quality sound and vibration instruments for various applications, including sound level meters. Some of the popular brands include:
Sound level meters are categorized into Class 1 and Class 2 based on their accuracy. Class 1 meters offer higher precision and are defined by criteria such as frequency response, sound pressure level range, and overall performance. These classifications guide users in understanding the meter’s capabilities and in choosing the right device for their application.
The IEC 61672-1 standard outlines the performance requirements for professional sound level meters, categorizing them into Class 1 and Class 2 based on their accuracy and operational capabilities. The main differences between IEC 61672 Class 1 and Class 2 sound level meters lie in their frequency range, linear operating range, and temperature operating range. Both types are designed for measuring sound levels, but Class 1 meters offer higher accuracy and are generally more expensive.
Frequency Range:
Linear Operating Range:
Temperature Operating Range:
Class 1 sound level meters provide the highest accuracy and are ideal for critical applications like scientific research and legal proceedings. They meet stringent specifications and are crucial in environments where a small margin of error is significant. Class 2 meters are less precise but still reliable, commonly used for basic industrial noise assessments or general environmental monitoring. The choice between the two depends on the required accuracy for the specific task.
Sound level meters are primarily used for measuring sound levels in various environments, serving as an essential tool for multiple applications including regulatory compliance, hearing protection, noise pollution monitoring, and sound quality optimization. In regulated industries like construction, manufacturing, and entertainment, these meters are crucial for ensuring compliance with noise level guidelines. They also help in identifying areas where noise levels could pose a risk to hearing health, thereby facilitating protective measures. Additionally, these meters are used to monitor and identify sources of environmental noise pollution. In specialized fields such as music production and audio engineering, sound level meters are employed to measure and optimize sound quality to meet industry standards.
Sound level meter measurements refer to the quantification of sound levels in decibels (dB), often adjusted through frequency and time weightings to provide more meaningful and representative data. These measurements can include Sound Pressure Level (SPL), Equivalent Continuous Sound Level (Leq), and peak, maximum, and minimum sound levels. Frequency weightings such as A, C, and occasionally B and Z are applied to align the measurements with human auditory perception. Time weightings like “Fast” and “Slow” are used to average fluctuating noise levels over specific periods, although they are not applied to linear, time-averaged measures like Leq or to peak measurements, which capture the highest instantaneous sound level. These various measurements and adjustments allow for a comprehensive assessment of sound levels in diverse settings, from environmental monitoring to occupational safety.
LAS refers to a specific time-weighted sound level measurement that employs both A-weighting and “Slow” time weighting. The A-weighting is designed to mimic the frequency sensitivity of human hearing, while the “Slow” time weighting uses a time constant of 1 second. This combination allows LAS to provide a smoothed-out, averaged measurement of fluctuating noise levels, making it suitable for assessing environments where sound levels vary but not too rapidly. The LAS measurement offers a snapshot of the sound level, adjusted for both human auditory perception and the temporal characteristics of the sound.
LAF refers to a specific time-weighted sound level measurement that uses both A-weighting and “Fast” time weighting. The A-weighting is applied to approximate the frequency sensitivity of human hearing, while the “Fast” time weighting uses a time constant of 125 milliseconds to quickly respond to changes in sound levels. This combination makes LAF particularly useful for capturing transient or quickly fluctuating noise levels in a way that is representative of how they would be perceived by the human ear.
Sound Exposure Level (SEL) is a measure that quantifies the total energy in a noise event and normalizes it to a 1-second period. This metric allows for the comparison of events of different durations by providing an equivalent level that would be produced if the energy of the noise were compressed into a single second. SEL is particularly useful for assessing the impact of short-duration, high-level noise events, such as blasts or impact noises, and is often used in industrial, environmental, and occupational health settings to evaluate the cumulative noise exposure over time.
Occupational noise exposure quantifies the noise levels that workers encounter in their workplaces over a specific duration. Measured in decibels and time, this exposure can lead to noise-induced hearing loss (NIHL), an irreversible condition caused by damage to the inner ear’s hair cells responsible for transmitting sound to the brain. The noise dose, expressed as a percentage of a daily permissible limit serves as an indicator of 8-hour noise exposure and is defined by OSHA standard 1910. In Europe, the daily noise exposure level is denoted as LEX, 8h, as per ISO 1999. This metric is an 8-hour extrapolation of LAeq measured during work hours.
Reverberation time measurements quantify the duration it takes for sound to decay by 60 decibels after the sound source has been silenced. This metric is crucial in assessing the acoustic properties of a room or space and is often used in architectural acoustics, audio engineering, and environmental noise studies. The reverberation time is typically measured using specialized equipment like sound sources and sound level meters, and the data is analyzed to optimize sound quality or to comply with specific acoustic standards.
Short Leq refers to the Equivalent Continuous Sound Level measured over a short period, typically less than one hour and sometimes as brief as milliseconds or microseconds. This measurement is particularly useful in specialized applications where quick assessments of noise levels are required or where noise levels are expected to vary significantly over short durations, such as in building acoustics or machinery testing. Unlike longer Leq measurements that provide a time-averaged representation of fluctuating noise levels, Short Leq focuses on capturing the sound level over a brief period to offer insights into transient or rapidly changing noise conditions.
When using a noise level meters, several best practices are crucial to keep in mind:
Several misconceptions about sound level meters are important to address. First, some people may assume that any device to measure decibels is accurate and reliable, regardless of the brand or model. In reality, the accuracy and reliability of an acoustic meter can vary widely depending on several factors, such as the type, calibration, and environmental conditions.
Second, some people may assume that using a noise measurement tool is straightforward and easy without realizing the potential for errors or misunderstandings in measurement and interpretation. Third, some people may assume that all dB meters are equally suitable for any application, without considering the specific requirements and standards for their industry or application. It is important to be aware of these misconceptions and to take steps to ensure accurate and reliable noise measurements with a sound level meter.
Technical aspects of sound level meters cover features, signals, accuracy, ranges, weighting filters, and calibration.
Sound level meters can have several standard and optional features in addition to measuring the sound pressure level (SPL). Some of the standard features include:
In addition to standard functions, a professional SLM can be upgraded with several application-specific options, such as:
Consider whether the above features are necessary for your specific application when selecting a sound level meter.
Frequency weighting in sound level meters is a technique used to adjust the measured sound levels to approximate the frequency response of human hearing. Common types of frequency weightings include A, C, and occasionally B and Z. A-weighting is the most widely used and is designed to mimic the sensitivity of human hearing at quieter volumes, making it particularly relevant for environmental and general-purpose noise assessments. C-weighting offers a flatter frequency response and is often used for measuring peak sound levels or in occupational settings. These weightings are applied to various measurements such as Sound Pressure Level (SPL), Equivalent Continuous Sound Level (Leq), and peak, maximum, and minimum sound levels to make the data more meaningful and aligned with human auditory perception.
Time Weighting in sound level meters refers to the exponential averaging method that adjusts the device’s response to fluctuating noise levels. This method acts as a “filter” on the incoming sound signal, based on the selected time constant, to provide a more representative measurement of the sound environment.
The “Fast” (F) time weighting has a time constant of 125 milliseconds and is suitable for measuring sounds that do not fluctuate too rapidly, offering a quick response to changes in sound level. The “Slow” (S) time weighting uses a time constant of 1 second and is ideal for measuring average sound levels in environments where the sound fluctuates rapidly, as it provides a smoothed-out reading. The “Impulse” (I) time weighting is designed for capturing sounds with sharp peaks, such as gunshots or fireworks, and has a shorter time constant of around 35 milliseconds to accurately measure the brief, intense nature of such sounds.
Several variables can impact the accuracy of a sound level meter, including the quality of the device, calibration, and adherence to international standards. Typically, higher-quality and more expensive meters are more accurate than cheaper models.
According to IEC 61672 standards, the accuracy is dependent on frequency, with the most significant accuracy provided at 1 kHz, which is the frequency used to check the SLM calibration.
At 1 kHz, the accuracy of Class 1 meters is +/- 0.7 dB, while for Class 2 meters, it’s +/- 1 dB. As the frequency moves further away from 1 kHz, the accuracy difference between Class 1 and Class 2 meters increases. For instance, at 4 kHz, the Class 1 accuracy is +/- 1 dB and Class 2 is +/- 3 dB.
It’s worth noting that certain low-cost decibel meters marketed for noise exposure measurements may not always be reliable or accurate. These meters may use low-quality components like microphones or amplifiers or they may be calibrated improperly. Additionally, they may not meet accuracy standards established by organizations such as the International Electrotechnical Commission (IEC) or the American National Standards Institute (ANSI).
The frequency range of a sound level meter refers to the range of frequencies that the device can measure. Professional meters follow standards set by organizations such as the International Electrotechnical Commission (IEC) and provide a specific range. It is important to note that these frequencies are the middle frequencies of 1/3 octave bands.
In addition to the standard frequency range, there are also specialized sound level meters that can measure:
When selecting a sound level meter, it is important to consider, if the acoustic measurements require the measurement of ultrasounds or infrasound waves, it is crucial to choose a microphone specifically designed for these purposes.
IEC and ANSI meters often quote a frequency range of up to 20 kHz because it cover the entire audible range for humans, from the lowest audible frequency of 20 Hz to the highest audible frequency of 20 kHz.
It’s worth noting that on the upper end of the range, the error margin for IEC and ANSI meters can be quite large. Specifically, for Class 1 meters, the error margin at 20 kHz ranges from +4 dB to negative infinity, indicating that accuracy is not guaranteed at this frequency in practice. As a result, professionals in the field recognize that 16 kHz is the upper limit of the audible range that can be accurately measured using a Class 1 sound level meter.
RMS, AC signal, and DC signal are terms commonly used in the context of sound level meters and audio signals. Understanding these concepts can be helpful when using a sound level meter or working with audio signals:
Regular calibration is essential to maintaining the accuracy and reliability of professional devices. Calibration involves adjusting the device to match a known reference standard, such as a sound calibrator. Sound level meters can drift over time due to various factors, including environmental conditions and component wear and tear. Even slight deviations from the reference standard can result in significant measurement errors and affect compliance with standards or regulations.
The frequency of calibration depends on its application. As a general rule, a professional meter should be submitted for periodic testing by an accredited laboratory every 1-2 years. In addition to this, users should perform an acoustic calibration using a sound calibrator before and after a series of daily measurements.
The frequency of calibration depends on the type and quality of the meter as well as the specific regulations or standards that apply to the application. Regulations may require annual calibration, while some industries may require more frequent calibration. Following the manufacturer’s instructions and calibration procedures is crucial to ensure accurate and reliable measurements.
If you are considering purchasing a sound level meter, several factors need to be taken into account:
An authorized SVANTEK consultant will help You with the details such as the required accessories for your noise monitoring task.
