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| Measuring Noise Levels |
| Decibel (dB) |
The unit most commonly used for measuring the intensity of sound or degree of loudness. |
| Frequency |
The rate that an oscillating signal repeats itself. The number of times per a specific time period a wave repeats itself. Generally measured in Hertz (Hz) |
| Wavelength |
In the context of sound and noise, wavelength refers to the distance between successive points of a wave. This is inversely proportional to frequency in that the higher the frequency, the shorter the wavelength. Understanding wavelength is crucial in analysing the characteristics of sound and how it behaves in different environments. |
| Octave Band Filters |
In terms of frequency, an ‘octave’ represents a doubling or halving of the pitch.
An ‘octave band filter’ is a type of frequency filter and splits the frequency range into smaller bands allowing the frequency content of the noise to be identified.
Analysing an octave band is useful in characterising the frequency content of sound and is often employed in noise assessments and environmental noise studies. |
| Reverberation |
The persistence of a sound after it is produced due to reflections from surfaces in the environment. |
| Noise Dose |
Noise dose refers to the total sound exposure to noise over a specific period, typically over an 8-hour workday. This is generally expressed as a percentage of a reference exposure level and is commonly used in occupational settings to assess the risk of hearing damage due to prolonged exposure to loud noise. |
| Sound Pressure Level (SPL) |
Sound pressure level is a measure of the intensity of a sound wave and is typically used to quantify the loudness of sound. It is expressed in dB.
SPL is based on pressure variation caused by soundwaves in the air and is commonly measured using a Class 1 or Class 2 sound level meter.
SPL is often used in environmental noise assessments and occupational safety to compare the intensity of sounds. |
| Sound Power Level (SWL) |
The sound power level is a measure of the total amount of sound energy radiated by a source per unit of time. It is expressed in decibels (dB). The sound power level is different from the sound pressure level, which measures the intensity of sound at a specific location. |
| Frequency Weightings |
Frequency weightings are electronic filters within an instrument which emphasise some frequencies and de-emphasise others. Since humans are most sensitive to frequencies between 500Hz and 6kHz, frequency weightings allow a sound level meter to more accurately represent what the human ear hears.
‘A’ Weighting - A standard weighting of the audible frequencies designed to reflect how a noise is perceived by humans.
‘C’ Weighting - Relates to low frequency sounds and is essentially flat or linear between 31.5Hz and 8kHz, the two -3dB or ‘half power’ points. Representative of how the human ear hears high or impulsive levels of sound.
‘Z’ Weighting - The flat frequency response of 8Hz to 20kHz ± 1.5dB. The actual noise made with no weighting for the human ear. More useful for determining sound source rather than the effect on humans. |
| Time Weighting |
The speed a sound level meter reacts to sudden changes in sound level pressure, determining how smoothly values are displayed.
Fast and Slow Weightings: A fast weighted sound level display reacts faster to sound pressure level changes whereas slow weighted sound level display reacts slower.
Impulse Weighting: Instrument will respond quickly to change in sound pressure level but will fall slowly. |
| Equivalent Continuous Sound Level (Leq) |
Leq is a measure used to represent a continuous or fluctuating sound level over a specific period of time. It is a way of expressing a constant noise level that, if present for the same duration, would result in the same total energy as the actual fluctuating noise.
Leq is commonly used in environmental noise assessments and occupational noise studies to provide a single value that represents overall noise exposure over a specific time-period. Leq helps to compare different scenarios and assessing compliance with noise regulations. |
| Peak Sound Level Pressure (Lpeak) |
The peak instantaneous sound level, in decibels, with no time weighting.
The Peak Sound Level Pressure is usually C-Weighted (LCpeak) and used in occupational noise settings rather than in environmental monitoring. LCpeak is effective at measuring the noise of impacts or explosions which may place workers at risk of acute acoustic trauma injuries.
Under the Australian Work Health and Safety Regulations, an LC,peak of 140 dB(C) is the instantaneous noise exposure limit for workers in accordance with AS/NZS 1269.1. |
| Lmax and Lmin |
The highest and lowest time-weighted noise level measured during a given period of time. Distinguished from Lpeak as they are based on a time-weighted sound level in dB whereas Lpeak has no time weighting and reflects the actual peak of the sound pressure wave. |
| LAeq,8h |
The eight-hour equivalent continuous A-weighted sound pressure level in decibels, referenced to 20 micropascals, determined in accordance with AS/NZS 1269.1.
This measurement reflects the total amount of noise a person is exposed to over the course of their day considering intensity and length of noise exposure.
Under the Australian Work Health and Safety Regulations workers cannot be exposed to above LAeq,8h of 85 dB(A) (A-weighted 85 dB average over 8 hours of work). |
| SLC80 (Sound Level Conversion valid for 80% of wearers) |
A rating number for sound protection used in Australia and New Zealand. The difference between sound pressure levels outside the hearing protection compared to the sound level under the hearing protection inside the ear. To find the minimum SLC80 required for hearing protection in the workplace subtract the maximum safe noise exposure level from the overall sound level in the environment. |
| Class |
A classification for hearing protection in Australia and New Zealand according to AS/NZS 1270:2002. Hearing protection devices are given a class from 1-5 depending on the level of hearing protection they provide based on the LAeq,8h or SLC80. |
| Noise and Sound Level Monitoring Equipment |
| Sound Level Meter (SLM) |
A compact, handheld instrument which measures the sound pressure level (generally correlates well with human perception of loudness) in an environment.
May be categorised as class 1 or 2 under IEC 61672-1:2013. Class 1 meters are precision grade, meeting a higher level of performance criteria. Class 2 are general grade and are appropriate for situations where a very high level of precision and accuracy is not required. |
| Acoustical Calibrators |
Used to set the sensitivity of the SLM microphone before and after field work. Acoustical calibrators do this by emitting a highly accurate sound pressure of a known level to the microphone of the SLM. |
| Noise Dosimeter |
Similar to an SLM, a noise dosimeter is designed to measure personal noise exposure. They are generally worn by a worker throughout the day to determine whether noise exposure health guidelines are complied with. |
| Noise Survey |
The term used to describe the process of undertaking sound measurements, generally in a workplace, to determine overall noise levels and whether relevant laws and regulations relating to noise exposure are being complied with. |
| Hearing Protection Fit Testing |
| Qualitative |
Qualitative tests involve a pass or fail screening that tests the subjective ability of an individual to detect a specific sound through their hearing protection. |
| Quantitative |
The fit testing instrument will determine a PAR value achieved by the wearer based on the level of noise reduction in the individual’s application of the specific hearing protection. Unlike qualitative tests, the PAR generated by a quantitative hearing fit testing device, such as the 3M E-A-Rfit Dual-Ear Validation System, provides a numerical, objective value of noise attenuation achieved by the individual. |
| Personal Attenuation Rating (PAR) |
Can be subtracted from the known noise exposure in an environment to provide an estimation of reduction in individual noise exposure when the hearing protection is worn. |
