Gracey & Associates
Noise and Vibration
Glossary - L
GLOSSARY INDEX:
A B C
D E F
G H I
J K L
M N O
P Q R
S T U
V W X
Y Z
L : Instantaneous Sound Level
L10 : noise level exceeded for 10% of the measurement, calculated by statistical analysis, may also be in the form L10(1 hour) to specify the measurement period. L10 is commonly used for traffic noise.
Any percentile from 0.01% through to 99.99% may be measured but L10 for traffic, and L90 or L95 for ambient or background levels are the most common statistics used.
LA10 : noise level exceeded for 10% of the measurement period, A-weighted , calculated by statistical analysis.
L-weighting : Linear weighting - all values are weighted equally in the specified range.
La : Acceleration Level
LAn : noise level exceeded for n% of the measurement period with A-weighted , calculated by statistical analysis - where n is between 0.1 and 99.9%.
LAE : Sound Exposure Level
LAeq : widely used noise parameter that calculates a constant level of noise with the same energy content as the varying acoustic signal being measured. The A denotes the A-weighting has been included and the eq indicates that an equivalent value has been calculated. Hence LAeq is the A-weighted equivalent continuous noise level.
The Leq parameter is used extensively in acoustics and comes in many guises, so we have a separate page dealing in more detail - click here.
LAF : the instantaneous time-weighted sound level measured with A frequency weighting and Fast time weighting, available at any time.
LAFmax : the maximum time-weighted sound level measured with A frequency weighting and Fast time weighting, during the measurement period.
LAFmin : the minimum time-weighted sound level measured with A frequency weighting and Fast Time weighting, during the measurement period.
LAF(SPL) : the sound pressure level - maximum time-weighted sound level during the latest second) is available ate any time. A denotes the A frequency weighting is used.
Lavg : averaged sound level with selectable exchange rate.
LCpeak : the maximum peak sound level during a measurement. C denotes that the C frequency weighting is used. Used for monitoring the peak levels.
LCpeak,1s : the maximum peak sound level during the latest second - is available at any time. C denotes that the C frequency weighting is used. Used for monitoring the peak levels.
Lday : Day Noise Indicator
Lden : Day-evening-night Noise Indicator
Ldn : Day-night Level
LE : Sound Energy Density Level
Leakage : in an FFT analyzer, the input signal is recorded in time blocks, called time records, and individual spectra are computed from each block of data. Because the input signal period is not synchronised with the duration of the time block, the signal will be truncated at the beginning and end of the block. This truncation causes an error in the calculation, which effectively spreads out, or 'smears', the spectrum in the frequency domain. This phenomenon is called leakage it reduces the accuracy of the measured levels of peaks in the spectrum, and reduces the effective frequency resolution of the analysis. Leakage is worst for continuous signals and rectangular window, and it is greatly reduced by use of the Hanning Window, which forces the signal level to zero at the ends of the data block.
Length : l : one of the SI base quantities.
The SI base unit of length is the metre, symbol m
Lep,d : Daily Personal Noise Exposure
LEPN : Effective Perceived Noise Level
Lep,w : Weekly Personal Noise Exposure Level .
Leq : Equivalent Continuous Sound Pressure Level .
Levening : Evening Noise Indicator
Level : a sound pressure level in dB means that it is calculated relative to the standard reference level of 20 μPa for airborne sound. The word "level" associates that figure with the appropriate standard reference level. In common usage the level of a signal is its amplitude, but strictly speaking the term should be reserved for the amplitude expressed on a decibel scale relative to a reference value.
LEX,8h : Daily Personal Noise Exposure
LF : Force Level
LFNR : Low Frequency Noise Rating
LI : Sound Intensity Level
Lleq : Impulse Weighted Average Sound Level
Linear Averaging : the process of adding together a sequence of spectra measurements and then dividing the total by the number of samples. The result is a true arithmetic average on a sample by sample basis. Averaging smoothes out random noise components in a spectrum - see also exponential averaging
Linear Momentum : p : = mass x velocity
Linear Weighting : all values are weighted equally in the specified range.
Line Drive : an input socket that can also provide power to drive a transducer.
Line Source : a sound source composed of many point sources in a defined line, such as a train, flow of traffic on a motorway, or constant aircraft take-offs and landings. Sound levels measured from line sources decrease at a rate of 3 dB per doubling of distance.
Line Spectrum : a line spectrum is a spectrum where the energy is concentrated at specific frequencies (lines or bins), as opposed to a continuous spectrum where the energy is smeared out over a band of frequencies. A periodic deterministic signal will have a line spectrum, and a random signal will have a continuous spectrum. Spectra generated by machine vibration signatures are always a combination of these two types.
Linear : a device or circuit with a linear characteristic means that a signal passing through it is not distorted.
LI,R : Residual Intensity
LK : Pressure Intensity Index
Lmax : Maximum Sound Level
Lmin : Minimum Sound Level
Ln : percentile level where 'n' is between 0.1 and 99.9% calculated by statistical analysis. - may also include other descriptors i.e. A, C, L or Z weightings.
Most common Ln values are A-weighted L10 and L90 levels.
Lnight : Night Noise Indicator
LNP : Noise Pollution Level
LnT : Standardized Impact Sound Pressure Level : the impact sound pressure level in a stated frequency band, corrected for the standardized reverberation time of 0.5 seconds. Laboratory measurement.
L'nT : Standardized Impact Sound Pressure Level : the impact sound pressure level in a stated frequency band, corrected for the standardized reverberation time of 0.5 seconds. Field measurement.
LnT,w : Weighted Standardized Impact Sound Pressure Level : single number quantity used to characterize the impact sound insulation of floors, based on laboratory measurement of LnT.
L'nT,w : Weighted Standardized Impact Sound Pressure Level : single number quantity used to characterize the impact sound insulation of floors, based on field measurement of L'nT.
Building Regulations : Approved Document E - preferred parameter.
Logarithmic : a logarithmic scale is a scale of measurement that uses the logarithm of a physical quantity instead of the quantity itself.
Presentation of data on a logarithmic scale can be helpful when the data covers a very large range of values - the logarithm reduces this to a more manageable range .
Logarithmic Amplitude Scale : critical vibration components usually occur at low amplitudes compared to the rotational frequency vibration. These components are not revealed on a linear amplitude scale because low amplitudes are compressed at the bottom of the scale. But a logarithmic scale shows prominent vibration components equally well at any amplitude. Moreover, percent change in amplitude may be read directly as dB change. Therefore, noise and vibration frequency analyses are usually plotted on a logarithmic amplitude scale.
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 : Loudness is a subjective assessment of a given sound intensity. The unit of loudness, called the phon, and is equal to a difference in sound intensity of one decibel. The number of phons of a given sound is equal to the number of decibels of a 1000 Hz tone judged by the listener to be equally loud. Two similar sound pressure levels or intensities, but with different frequencies are generally judged as having different loudness, so SPL is not always a good measure of loudness when we compare tones of different frequencies. Equal loudness contours, have been arrived at by group consensus.
Low Frequency Noise Rating : LFNR : for example - LFNR 35.
Lp : Sound Pressure Level
LPac : Sound Power.
LPEAK : Peak Sound Level - may also include other descriptors i.e. A, C, L or Z weightings
LRPI : Residual Pressure Intensity Index
LSEL : Single Event Noise Exposure Level : the dBA level which, if it lasted for one second, would produce the same A-weighted sound energy as the actual event - see also sound exposure.
Lv : Velocity Level
LW : Sound Power Level.
GLOSSARY INDEX:
A B C
D E F
G H I
J K L
M N O
P Q R
S T U
V W X
Y Z
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