Elliot Kim
A sound level meter (SLM) is a portable instrument used to measure sound pressure levels. It is designed to respond to sound in a similar way to the human ear and provide reproducible measurements of sound pressure levels (SPL). Sound level meters are used to measure and manage noise from various sources, including industrial plants, traffic, and construction work. They are also used in noise pollution studies to quantify different types of noise, such as industrial, environmental, mining, and aircraft noise. The device consists of a microphone, a preamplifier, signal processing, and a display. The microphone converts sound signals into electrical signals, which are then amplified and processed to provide measurements in decibels (dB). Sound level meters are categorized into different classes based on their accuracy, with Class 1 being precision-grade and Class 2 being general-purpose grade.
| Characteristics | Values |
|---|---|
| Name | Sound Level Meter (SLM) |
| Other Names | Sound Pressure Level (SPL) Meter, Decibel (dB) Meter, Noise Meter, Noise Dosemeter, Noise Dosimeter, Personal Sound Exposure Meter (PSEM) |
| Type of Instrument | Commonly hand-held, compact, portable, battery-powered |
| Function | Measures sound pressure levels in a standardised way, responding to sound in a similar way to the human ear |
| Microphone | Condenser microphone, which converts sound signal to an electrical signal |
| Microphone Sensitivity | Must be known to the instrument to accurately convert the electrical signal back to sound pressure |
| Signal Processing | Includes applying frequency and time weightings as specified by international standards such as IEC 61672-1 |
| Time Weightings | Fast (F), Slow (S), Impulse (I) |
| Frequency Weightings | A, C, Z |
| Display | Shows sound pressure levels in decibels (dB) and frequency analysis in Hertz (Hz) |
| Classes | Class 1 (precision-grade), Class 2 (general-purpose) |
| Accuracy | Class 1: +/- 0.5 dB, Class 2: +/- 1.0 dB |
| Frequency Range | Class 1: 16 Hz to 16 kHz, Class 2: 20 Hz to 8 kHz |
| Dynamic Range | Minimum dynamic range of 60 dB between lowest and highest measurable dB levels |
| Uses | Noise pollution studies, quantification of different kinds of noise, measurement of ambient noise levels, workplace safety, hearing damage risk measurements |
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What You'll Learn
Sound level meter classes
Sound level meters are classified into two classes, as per the IEC 61672 standard. These classes are designated based on the device's accuracy and precision. Class 1 meters offer higher accuracy, a broader frequency range, and a wider temperature operating range than Class 2 meters.
Class 1 sound level meters are suitable for detailed and precise acoustic measurements and are often used in research and law enforcement. They are best employed in laboratory settings for precision-grade assessments. The frequency range for Class 1 meters is from 16 Hz to 16 kHz, and they have an accuracy of +/- 0.7 dB at 1 kHz.
Class 2 sound level meters, on the other hand, are generally used for basic noise assessments and are adequate for most applications. They are commonly used in industrial, commercial, educational, recreational, or residential settings. The frequency range for Class 2 meters is from 20 Hz to 8 kHz, and they have an accuracy of +/- 1 dB at 1 kHz.
It is important to note that the class of meter chosen depends on the specific application and any regulations that need to be met. For example, the European Noise at Work Regulations state that a Class 2 meter is sufficient, but a Class 1 meter can be used if higher accuracy is required.
In addition to these two main classes, the American National Standards Institute (ANSI) specifies three different types: Type 0, Type 1, and Type 2. These types are described in the Occupational Safety and Health OSHA Technical Manual and set performance and accuracy tolerances.
Furthermore, there are specialized variants of sound level meters, such as the noise dosemeter or noise dosimeter, which is a body-worn instrument used to measure an individual's noise exposure over a period, typically to comply with health and safety regulations.
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Microphone sensitivity
A sound level meter (SLM) is a device used to measure sound levels in a standardized way. It is designed to respond to sound in a manner similar to the human ear and provide objective, reproducible measurements of sound pressure levels. The microphone is a crucial component of the SLM, as it captures the sound and converts it into an electrical signal for further processing.
The microphone's diaphragm vibrates in response to sound pressure waves, and this movement is converted into an electrical signal. The sensitivity of the microphone determines how much audio signal is produced for a given input sound pressure level. A microphone with higher sensitivity will "pick up" quieter sounds due to a more sensitive diaphragm.
The standard reference sound pressure level for measuring microphone sensitivity is a 1,000 Hz tone at 94 dB-SPL (1 Pascal or 10 microbars). The output voltage is then measured in dBV (decibels relative to 1 Volt) or millivolts (mV). This information is typically provided in the product data sheet for professional microphones.
It is important to note that the sound level meter itself needs to know the sensitivity of the particular microphone being used. This allows the instrument to accurately convert the electrical signal back into sound pressure and display the resulting sound pressure level in decibels (dB). Therefore, microphone sensitivity is a critical aspect of the sound level meter's functionality, enabling it to provide accurate and reliable measurements of sound pressure levels.
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Frequency weightings
Sound level meters are designed to respond to sound in the same way as the human ear and to provide reproducible measurements of sound pressure levels. The frequency weightings used in sound level meters are related to the response of the human ear to ensure that the meter is measuring what you actually hear.
Frequency weighting adjusts how the sound level meter responds to different sound frequencies. The human ear responds more to frequencies between 500 Hz and 8 kHz and is less sensitive to very low-pitch or high-pitch noises. The most common weighting used in noise measurement is A-Weighting, which effectively cuts off the lower and higher frequencies that humans cannot hear. A-weighting is mandated by international standards for civil aircraft noise measurements and for the protection of workers against noise-induced hearing loss.
C-weighting is also available on many sound level meters and is used for peak measurements and in some entertainment noise measurements, where the transmission of bass noise can be a problem. C-weighting is more sensitive to lower frequencies and represents what humans hear when the sound is loud (near 100 dB SPL).
Z-weighting is a flat frequency response of 10 Hz to 20 kHz ±1.5 dB. This response replaces the older "Linear" or "Unweighted" responses as these did not define the frequency range over which the meter would be linear. Z-weighting is used mainly for detailed frequency analysis, providing an unweighted measurement of sound pressure levels across the entire frequency range.
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Time weightings
Time weighting, also known as time-weighting, refers to how a sound level meter reacts to changes in sound pressure over time. It is an exponential averaging of the fluctuating signal, providing an easy-to-read value.
The three standardised time weightings are:
- Slow (denoted by 'S' or 'L'): Slow weighting has a one-second response time. This means it takes one second for the sound level meter to get up to the level of a constant tone. It is good at "ignoring" short, fast sounds like car doors slamming or balloons popping. It is the smoothest of the three weighting types, providing an "average" sound level. This makes it a good choice for environmental noise studies, especially those that span many hours or days.
- Fast (denoted by 'F' or 'L'): Fast weighting responds to changes in sound in 0.125 seconds (125 milliseconds), which is about eight times faster than the slow weighting response. It is more responsive to short, fast sounds than slow weighting. Fast weighting provides a higher resolution and a more detailed picture of the measured sound. It is most commonly used in environmental noise assessments.
- Impulse (denoted by 'I'): Impulse weighting is the least common of the three types. It was originally designed to measure sound levels for impulses—short, loud sounds, like gunshots and explosions. It has the quickest response time of 0.035 seconds or 35 milliseconds, which is about four times faster than fast weighting. Impulse weighting has a slow decay, meaning it takes longer for the reading to drop back down.
The choice between these time weightings depends on the specific application and the type of sound being measured. For example, the slow characteristic is used when the reading with the fast response fluctuates too much to give a reasonably well-defined value.
These time weightings are applied to the signal as specified by international standards such as IEC 61672-1, to which sound level meters conform. The sound pressure level values are updated at least once per second and are displayed in decibels (dB) referenced to 20 micropascals (µPa) on the analyzer's screen.
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Uses of sound level meters
A sound level meter (also called a sound pressure level meter (SPL)) is a measuring instrument used to assess noise or sound levels by measuring sound pressure. It is commonly a hand-held device with a microphone that converts sound waves into electrical signals. The microphone sensitivity allows the instrument to convert the electrical signal back to sound pressure. The sound level is then displayed in decibels (dB).
Sound level meters have various uses, including:
Noise Pollution Studies
Sound level meters are commonly used in noise pollution studies for the quantification of different kinds of noise, especially in industrial, environmental, mining, and aircraft noise contexts. They are also used to measure and manage noise from road and rail traffic, construction work, concerts, and leisure parks.
Workplace Safety
Portable sound level meters can be used by workplace safety professionals to measure sound levels in multiple locations, ensuring that environmental conditions fall within recommended exposure limits.
Health and Safety Compliance
A specialized variant of the sound level meter, called a noise dosemeter (or dosimeter in American English), is used to measure the noise exposure of a person over a period of time. This is often used to comply with Health and Safety regulations, such as the Occupational Safety and Health (OSHA) Occupational Noise Exposure Standard.
Long-Term Monitoring
Sound level meters can be used for long-term monitoring in various environments by continuously recording noise levels, allowing for the identification of trends or patterns in noise exposure.
Basic Noise Assessments
Class 2 sound level meters are typically used for general noise assessments, while Class 1 meters offer higher accuracy and a wider frequency response range, making them suitable for detailed and precise acoustic measurements.
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Frequently asked questions
A sound level meter (SLM) is a compact, portable instrument used to measure sound pressure levels. It responds to sound in a similar way to the human ear and provides objective, reproducible measurements of sound pressure levels.
Sound pressure is the average variation in atmospheric pressure caused by sound. The unit of measurement for sound pressure is the Pascal (Pa).
A sound level meter uses a microphone to capture sound. The microphone converts the sound signal into an electrical signal. This electrical signal is then amplified and processed, with various weightings applied, before being displayed as a sound pressure level in decibels (dB).
Sound level meters are used to measure and manage noise from various sources, including industrial plants, traffic, construction work, concerts, and residential areas. They are often used to ensure compliance with noise regulations and assess the suitability of noise levels for workers and occupants.
