Kiera Jefferson
Noise pollution is a growing environmental problem that can have adverse effects on human health and well-being. It refers to any unpleasant, damaging or irritating noise that has the potential to harm people, wildlife or the environment. The decibel (dB) is the main unit used to measure the intensity or loudness of sound waves, with a 10-point increase in dB level representing a 10-fold increase in noise level. To measure sound pollution, commercially available sound level meters are used to measure the sound intensity in decibels. The sound pressure level is measured to determine noise exposure, and the meter is placed where people are supposed to listen to the sound. For example, when measuring traffic noise, the meter is placed on the pavement. There are two types of sound level meter: Class 1 and Class 2. A Class 1 sound level meter is considered more accurate than Class 2 due to its narrower tolerance limits.
| Characteristics | Values |
|---|---|
| Main instruments used for measuring noise | Sound level meter (SLM), integrating sound level meter (ISLM), and noise dosimeter |
| How SLM works | It consists of a microphone, electronic circuits, and a readout display. The microphone detects small air pressure variations associated with sound and changes them into electrical signals. These signals are then processed by the electronic circuitry of the instrument. The readout displays the sound level in decibels. |
| How to use SLM | The SLM is held at arm's length at ear height for those exposed to the noise |
| Calibration | Calibrators are used to adjust sound level meters to the reference sound pressure level and to check that it is maintained after measurement. |
| Noise immission | The reception and exposure to noise generated by an emitting source. It is measured in decibels and is used to assess the noise levels to which a person or community is exposed. |
| Sound intensity | Whisper: 20 dB; Quiet office: 40 dB; Normal conversation: 60 dB; Pain threshold: 80 dB; Dangerous for ears: 90 dB; Rupturing eardrums: 200 dB |
| Noise sources | Road traffic, faulty car or burglar alarms, noisy electrical appliances, construction, leaf blowers, loud music, etc. |
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What You'll Learn
Sound level meters
A sound level meter is a hand-held device with a microphone that measures sound pressure levels (SPL) in Pascals and converts them into decibels (dB). The diaphragm of the microphone responds to changes in air pressure caused by sound waves, and this movement is converted into an electrical signal. The sound pressure level is then stated in decibels, with 0 dB SPL equal to 20 micropascals.
There are two main types of sound level meters: Class 1 and Class 2. Class 1 meters are considered more accurate due to their narrower tolerance limits. These meters are used to conduct acoustic surveys in various areas to assess noise indices and determine compliance with regulations.
When using a sound level meter, it is important to select the appropriate equipment, position the microphone correctly, and record data over a defined period. Measurements should consider factors such as height and distance from the noise source, as well as frequency, duration, and intensity. The results are then analyzed to ensure compliance with noise regulations and to identify areas for potential noise reduction.
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Decibel (dB) measurements
Sound pressure level (SPL) is a measurement of loudness (amplitude) and is expressed in decibels (dB). The C-weighted (dBC) scale is used for impact noise levels, such as gunfire, and is more accurate than dBA for the perceived loudness of sounds with low-frequency components. The A-weighted filter is commonly used for measuring ambient community noise and the results are expressed as A-weighted decibels or dBA.
Equivalent sound levels (Leq) are used to express the average SPL over a period, such as an eight-hour workday. Leq is a logarithmic average, so louder events are given more weight in the overall result. Another unit, the day-night sound level (DNL or Ldn), accounts for the fact that people are more sensitive to noise at night, so a 10-dBA penalty is added to SPL values measured between 10 pm and 7 am. DNL is useful for describing overall community exposure to aircraft noise.
To measure sound pollution, instruments such as the sound level meter (SLM), integrating sound level meter (ISLM), and noise dosimeter are commonly used. The SLM consists of a microphone, electronic circuits, and a readout display. The microphone detects small air pressure variations associated with sound and converts them into electrical signals, which are then processed by the electronic circuitry. The readout displays the sound level in decibels. The SLM takes the sound pressure level at one instant in a particular location and is held at arm's length at ear height for those exposed to the noise. The ISLM is used when a worker spends most of their shift in a defined location or moves to different areas during the shift. It provides equivalent sound level measurements and an accurate exposure assessment.
Noise dosimeters are worn by workers during the entire measurement period and record sound levels. The manufacturer's instructions must be followed, and the device should be calibrated before and after each measurement. If the calibration is off by more than 0.5 dB, resampling may be required.
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Noise immission
Sound pressure is the small variation above and below atmospheric pressure created by the passage of a sound wave. This is what most people think of as noise. Pressure sensed by a microphone on a sound-level meter is generally converted to a mean square pressure or pressure level by the measuring instrument. The level indicated by the sound-level meter will fluctuate depending on the averaging time of the measuring system. The sound pressure may be converted into a metric that more closely relates to human response, such as the effective perceived noise level used to specify the noise emissions of airplanes.
Noise calculation is the process of calculating the level of noise immission using the metric dB(A). Noise immission is created by noise sources (noise emission) of various types, which propagate noise into the environment. A single source will create a certain level of immission, primarily driven by the originating sound power level and distance influenced by factors such as absorption and reflection. Several noise sources typically result in higher levels of immission. The method or process of determining the resulting immission level is called noise calculation, and its graphical representation is called a noise map.
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Calibrators
Calibration is an important step in sound measurement, especially when it comes to health and safety and maintaining accurate measurements over time. Calibrators are devices that produce a stable sound at a given level and frequency. They are used to adjust sound level meters to a reference sound pressure level and to ensure that this level is maintained after measurement.
Sound level meters, also known as noise level meters, decibel meters, audio level meters, and acoustic measurement devices, are used to measure noise levels in the environment, such as in residential areas, near transportation routes, or around construction sites. They are also used in acoustics research to measure sound levels and analyse sound characteristics such as frequency, amplitude, and duration. These meters consist of a microphone, electronic circuits, and a readout display. The microphone detects small air pressure variations associated with sound and converts them into electrical signals, which are then processed and displayed as a sound level in decibels.
There are two types of sound level meters: Class 1 and Class 2. Class 1 meters are considered more accurate due to their narrower tolerance limits. These meters are used to conduct acoustic surveys in various areas, including urban, industrial, traffic, and residential settings, to assess noise indices and determine compliance with regulations. Local governments and authorities are responsible for regulating and controlling noise pollution, drawing up noise maps, and monitoring compliance with laws that regulate noise levels.
Sound dosimeters are another instrument used to measure noise exposure over time. These devices are worn by individuals and must be calibrated before and after each measurement. If the calibration is off by more than 0.5 dB, resampling may be required as the results may not be accurate.
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Noise dosimeters
There are various noise dosimeters available on the market, such as the doseBadge Industrial Noise Dosimeter, which meets OSHA and NIOSH regulations. The OSHA version of the doseBadge has two channels, one measuring at 80 dB and the other at 90 dB, to meet the different requirements of these regulations. The NIOSH version has one channel set to NIOSH requirements and another that can be configured to meet other regulations. The device is small and lightweight, ensuring it does not interfere with the worker's duties.
RAECO Rents offers the SKC NoiseCHEK, TSI Quest Edge 5, and Casella dBadge2 IS personal noise dosimeters, which are all rated as intrinsically safe. These devices provide personal exposure data and help establish the need for personal hearing protection equipment and the permissible period an employee can safely work in a specific area.
The use of noise dosimeters offers several benefits over other methods of measuring noise exposure, such as hand-held sound level meters. Dosimeters automatically measure and calculate noise exposure, eliminating the need for manual calculations. They also allow for the measurement of noise exposure in hazardous environments or areas where it is impractical to follow the worker to each location.
It is important to note that noise dosimeters should be calibrated before and after each measurement to ensure accurate results. Additionally, the device should be fitted to the worker at the start of the day or shift and left to measure the total noise exposure.
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Frequently asked questions
Sound level meters (SLMs), integrating sound level meters (ISLMs), and noise dosimeters are the most common tools used to measure sound pollution.
The decibel (dB) is the main unit used to measure the intensity or loudness of sound. A sound can also be measured by its pitch, which is the frequency of sound vibrations per second.
The first step is to determine whether noise is a problem in the environment or workplace. If it is, the next step is to use a sound level meter to measure the sound and compare it to the recommended sound levels. It is important to note the distance between the meter and the source of the sound, the direction the noise source is facing, and whether the measurement is taken indoors or outdoors.
