Glossary of common noise terminology
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Glossary of common noise terminology |
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The following terms are often encountered in noise
measurements. |
| Terminology | Brief definition | Abbrev. | Symbol | Unit |
| 'A' weighting
|
the frequency correction curve applied in a sound level meter to a sound to mimic the response of the human hearing | dB(A) | A | |
| Anechoic chamber
|
a room with no echoes such as a special test room where the inside surface is covered with absorbent foam wedges to minimize reflections | |||
| Accuracy
|
for the measurement of noise levels by a sound level meter the required accuracy is laid down in the appropriate ANSI standards covering sound level meters, calibrators, dosimeters and filter sets | |||
| ANSI
|
the American body that publishes the standards used by the acoustics professionals, stands for the American National Standards Institute | ANSI | ||
| ASTM
|
the American body that publishes standards outlining how to carry out certain acoustic measurements so that the results can be compared between different users, stands for the American Society for Testing Materials | ASTM | ||
| Average noise level
|
the average single number noise level over a given period of time with a stated exchange rate | Lavg | dB | |
| Background noise
|
the overall sum of all the noise present at a specific location and time usually measured or referred to without the presence of the main noticeable offending noise | |||
| Broadband noise
|
noise covering the whole of the audio range of frequencies and usually measured with one of the standard frequency weighting filters | |||
| 'C' weighting
|
the frequency response often used to measure very high noise levels | dB(C) |
C |
|
| Community noise
equivalent level
|
the 24 hour average noise level of all hourly Leq measurements with a 10 dB penalty added to the levels between 2200 and 0700 hours and a 5 dB penalty added to the levels between 1900 and 2200 hours to reflect people's extra sensitivity to noise during the night and the evening | CNEL |
Lden |
dB |
| Criterion level
|
the steady equivalent sound level lasting for exactly 8 hours that corresponds to the 100% noise dose value | Cri |
dB | |
| Day night level
|
the 24 hour average noise level of all hourly Leq measurements with a 10 dB penalty added to the levels between 2200 and 0700 hours to reflect people's extra sensitivity to noise during the night | DNL |
LDN |
dB |
| Dose Badge
|
a small light weight unit that can be worn by an operator to store the changing noise levels during a workday. it has no display nor keypad so cannot be tampered with during the time it is worn. a separate reader unit is required to see the noise level results | |||
| Dosimeter
|
a small lightweight instrument designed to be worn during all or part of the day as a personal monitor in order to check an operator’s exposure to workplace noise | |||
| decibel
|
a dimensionless unit of acoustic measurement in sound level meters where 0dB is the threshold of normal hearing and 130 dB is the threshold of pain | dB |
(dB) |
dB |
| Exchange rate
|
the number of decibels that noise in the workplace has to increase by to be considered as being twice the harmful risk to hearing, usually has the value of 3 for equal energy measurements for European regulations (or measurements following the ACGIH recommendations) and a value of 5 for noise measurements to the US OSHA or MSHA noise regulations | Q |
Q |
dB |
| Fast Fourier Transform
|
a mathematical calculation used to obtain very narrow band data analysis of a noise signal in which the whole audio spectrum is commonly divided up into 400 lines of frequency data with a linear step interval | FFT | FFT | Hz |
| Fast response
|
a 1/8 second averaging time in the detector of a sound level meter | Fast |
F |
sec |
| Frequency
|
the small fluctuations in a sound that cover the audible range of tones from about 20 Hz to about 20 kHz for the normal hearing of an adult | Hz |
Hz |
Hz |
| Frequency analysis
|
analyzing an overall broadband noise to identify the different contributions in different parts of the audio spectrum | |||
| Impulse response
|
an asymmetric averaging time in the detector of a sound level meter with a 35/1000 second response to increasing signals and a 1500/1000 second response to decreasing signals | Impulse |
I |
|
|
ISO
|
the international body that publishes the standards used by the acoustics professionals, stands for the International Standards Organization, deals with how acoustic measurements are to be performed | ISO | ||
| Lavg
|
the average noise level over a period of time that uses an exchange rate of 4, 5 or 6 in the calculation of the final value | Lavg | Lavg(5) | dB |
|
Leq
|
the equivalent continuous noise level that contains the same amount of noise energy as the actual varying noise, the Leq is a special case of the Lavg with the Q=3 exchange rate | Leq | LAeq | dB |
| Logging
|
the process of saving noise data at short regular intervals of time so that a picture of the variations can be studied at the end of a long measurement, usually logging is carried out at 1 second or 1 minute intervals but it can be as much as 1 hour in some cases | |||
| Loudness
|
the objective measurement of a sound that is calculated from its level and frequency distribution, usually measured with a real time third octave band analyzer to capture the variations across all parts of the audio spectrum | Sones | ||
| Maximum sound level
|
the highest reading with a specified frequency weighting and time response in a sound level meter | Lmax |
Lmx |
dB |
| Minimum sound level
|
the lowest reading with a specified frequency weighting and time response in a sound level meter | Lmin |
Lmn |
dB |
| Noise
|
most often defined as the presence of unwanted sounds, can be damaging to hearing if it is too loud or can be just annoying if it interferes with the normal enjoyment of others | |||
| Noise dose
|
the amount of noise expressed as a percentage of the normal allowable daily collected during a measurement on a worker with a noise dosimeter | Dose% |
% | |
| Noise reduction rating
|
the single number figure that gives an approximate method for choosing personal hearing protectors for workers in noisy industries, compare with the figure on the protector to choose the best one for the specific noise source under investigation | NRR | NRR | dB |
| Octave band analysis
|
analyzing a noise into smaller ranges of frequency where the normal audio range is split up into 9 or 10 separate bands each of which is an octave wide | |||
| Ordinance
|
a law passed by a local town or city or state to indicate any limits that have been imposed on the production of offending noises in the community, may be written in simple overall 'A' weighted terms or may require octave band measurements to control tonal problems | |||
| Peak response
|
an equivalent averaging time of less than 0.0001 seconds in the detector of a sound level meter | Pk |
P |
|
| Peak sound level
|
the absolute highest sound pressure of the noise signal of either the positive or negative part of the sound wave | Lpeak |
Lpk |
dB |
| Percentile sound level
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the noise level, in decibels, exceeded for N % of the total measurement time such that the 10% level for an hour is the noise level exceeded for 6 minutes in total | LN% |
LN% |
dB |
| Periods
|
the regular storage of noise levels during a run over medium to long term intervals such as 1 minute to 1 hour duration | |||
| Permissible exposure
level
|
the 8 hour allowable long term noise level for a working days exposure | PEL |
dB | |
| Pink noise
|
broadband noise across the whole audio spectrum that contains an equal amount of energy in all octave or third octave bands | |||
| Profiles
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the storage of regular noise levels during a measurement to show how the noise varied with time, usually taken at short intervals such as 1 sec up to 1 minute | |||
| Projected noise dose
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what the final value of the noise dose would be at the end of 8 hours if the shorter measurement was to continue with the noise pattern remaining the same | Proj dose% | % | |
|
Q
|
the risk factor for workplace noise measurements from 3 to 6 depending on the protocol being followed, (see also exchange rate) | Q | Q | dB |
| Real time frequency
analysis
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the measurement of octave or third octave bands of noise where all the filters are measured for all the different bands at the same time, suitable for impulsive or steady noise signals | |||
| Reverberation chamber
|
a specially constructed test room in which all the surfaces are hard and reflective so that none of the noise produced will be lost by absorption, often used for the measurement of sound power levels of noisy machines | |||
| Reverberation time
|
the time taken for a sound pressure to drop by 60 dB in an enclosed space such as a room | RT | T60 | sec |
| Serial frequency
analysis
|
the measurement of octave or third octave bands of noise where a single filter is stepped across the different bands one at a time, suitable mainly for steady noise signals only | |||
| Slow response
|
a 1 second averaging time in the detector of a sound level meter | Slow |
S |
|
| Sone
|
the unit used to assess the loudness of a noise that depends on its spectral content and level | Sone | Sone | |
| Sound exposure level
|
the equivalent continuous noise level of an event including all the actual noise then referenced to a notional duration of 1 second | SEL |
LAE |
dB |
| Sound power level
|
the total amount of noise inherent in a particular noise source independent of the acoustic environment that it is in | W |
LW |
dB |
| Sound pressure level
|
the instantaneous changing sound level with a selected frequency weighting and time response | SPL |
Lp |
dB |
| Time average sound level
|
the equivalent steady level over a given period of time that contains the same amount of noise energy as the actual changing noise level | Leq |
Leq |
dB |
| Time weighted average
level
|
the total amount of workplace noise exposure expressed as an equivalent standard 8 hour working day | TWA |
TWA |
dB |
| Third octave band
analysis
|
analyzing a noise into smaller ranges of frequency where the normal audio range is split up into 27 or 30 separate bands each of which is a third octave wide | |||
| Threshold level
|
the sound pressure level below which an instrument will ignore any readings to include in noise dose measurements | Thr |
dB | |
| Transmission loss
|
the difference between the noise levels across a partition between two or more rooms | TL |
dB | |
| Vibration
|
movements of a body such as a machine or fan that are transmitted through the structure and detected as a motion with a given amplitude and frequency | |||
| White noise
|
broadband noise across the whole audio spectrum that contains an equal amount of energy in all frequencies when measured on a linear frequency scale | |||
| 'Z' weighting
|
the "zero" or un-weighted frequency correction curve corresponding to the Linear setting on some instruments | dB(Z) |
Z |