Definitions, Terms, Units and Parameters

L

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LA

LA10

: is the noise level just exceeded for 10% of the measurement period, A-weighted and calculated by statistical analysis.

LA90

: is the noise level exceeded for 90% of the measurement period, A-weighted and calculated by statistical analysis.

LAn

: noise level exceeded for n% of the measurement period with A-weighted , calculated by statistical analysis - where n is between 0.01% and 99.99%.

The LA10 and LA90 are extensively used for rating traffic noise and background noise respectively

The measurement period should also be stated. For example, LA10(18-hour) is considered good practice when reporting Road Traffic Noise measurements,

See also background noise

LAE : Sound Exposure Level

LAeq

: A-weighted, equivalent sound level.

A widely used noise parameter describing an sound level with the same energy content as the varying acoustic signal measured. Also written as dBA Leq. .. more details

LAT : Time Averaged Level

: the equivalent steady level over a given period of time that contains the same amount of noise energy as the actual fluctuating level

see also Leq - the equivalent continuous noise level

Lavg

: averaged sound level with selectable exchange rate.

LC

: C weighted, sound level.

LCE

: C weighted, sound exposure level

LCeq

: C weighted, Leq. sound level

LCF

: C weighted, Fast, sound level.

LCFmax

: C weighted, Fast, maximum, sound level.

LCpeak

: C weighted, Peak, sound level.

LCS

: C weighted, Slow, sound level.

LCSmax

: C weighted, Slow, maximum, sound level.

LCSmin

: C weighted, Slow, minimum, sound level.

Lday : Day equivalent level

: A weighted, Leq. noise level, measured over the 12-hour period 07.00 - 19.00 hours.

Also known as Day Noise Indicator and other terms.

Lden : Day-evening-night equivalent level

: A weighted, Leq. noise level, measured over the 24 hour period, with a 10 dB penalty added to the levels between 23.00 and 07.00 hours and a 5 dB penalty added to the levels between 19.00 and 23.00 hours to reflect people's extra sensitivity to noise during the night and the evening.

See also Community Noise Equivalent Level - CNEL.

Ldn : Day-night equivalent level

: A weighted, Leq. noise level, measured over the 24 hour period, with a 10 dB penalty added to the levels between 23.00 and 07.00 hours.

Also known as the Day-night Noise Indicator and other terms.

LE : Sound Energy Density Level

Leakage

: in an FFT analyser, 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

Leq

: the Equivalent Continuous Sound Level is the preferred single value figure to describe sound pressure levels that vary over time and would produce the same sound energy over the stated period of time T.

It is good practice to include other measurement parameters such as A-weighting and the measurement period, for example LAeq,t.

If the Leq is measured over 8 hours then Leq = LEP,d = LEX,8h = %Dose.

Leq is widely used, but not widely understood, so we include

more Leq details here.

Sometimes also known as the LAT - time averaged level

See also Short Leq

Also known as the Equivalent Sound Level and Equivalent Noise level.

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.

Levening : Evening equivalent level

: A weighted, Leq. sound level, measured during the evening period 19.00 - 23.00 hours.

Also known as the Evening Noise Indicator and other terms.

LEX,8h :

Daily Exposure Level - see also Daily Personal Noise Exposure LEP,d

LF : Force Level

LFNR : Low Frequency Noise Rating

Lg : Logarithm

Li : Impact Sound Pressure Level

LI : Sound Intensity Level

LIeq : Impulse Weighted Average Sound Level

: used in Germany, defined by DIN 45641 : 3 dB exchange rate.

Linear

: a device or circuit with a linear characteristic means that a signal passing through it is not distorted.

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.

Other averaging methods : Exponential RMS Spatial Spectrum Time Domain

Linear Momentum : p

: = mass x velocity

Linear Weighting

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.

LI,R - Residual Intensity

LK - Pressure Intensity Index

Lmax : Maximum Sound Level

: level during a measurement period or a noise event.

Do not confuse with PEAK.

Should also include other descriptors i.e. A, C, L or Z weightings and F, S or I time constants.

Sometimes written as Max dB(A).

Lmin : Minimum Sound Level

: during a measurement period or a noise event.

Should also include other descriptors i.e. A, C, L or Z weightings and F, S or I time constants.
Sometimes written as Min dB(A).

Ln : Logarithm

Ln

: percentile level where 'n' is between 0.01 and 99.9% calculated by statistical analysis.

Usually include a descriptor i.e. A-weighting.

Most common Ln values are LA10 and LA90 levels.

Ln : Normalised Impact Sound Pressure Level

Lnight : Night equivalent level

: Leq. A weighted, sound level, measured overnight 23.00 - 0700 hours.

Also known as the Night Noise Indicator and other terms.

Lnp : Noise Pollution Level

LnT : Standardized Impact Sound Pressure Level
L'nT : Standardized Impact Sound Pressure Level
LnT,w : Weighted Standardized Impact Sound Pressure Level
L'nT,w : Weighted Standardized Impact Sound Pressure Level

Logarithm : Log, log, lg, Ln

: a logarithmic scale is a scale of measurement that uses the logarithm of a physical quantity instead of the quantity itself. Common logarithms are widely used in science and engineering.

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. For example 120 dB is 'equivalent' to 1,000,000 relative to 0 dB sound level - see the decibel for full details.

The common logarithm is the logarithm to the base 10 and is often written as log10(x) or Log(x) but this can be ambiguous or confusing as Log on a calculator often refers to natural logarithms, favoured by mathematicians, with a base of e (~2.718). The binary logarithms to the base = 2 is used in computer science.

To overcome this problem ISO, the International Standards Organisation, recommend:-
log10(x) should be written lg (x) and
loge(x) should be written ln (x).

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 recording noise data results at regular intervals of time so that a 'picture' of the variations can be studied at the end of a long measurement. Usually results are logged at 1 second or 1 minute intervals but it can be as much as 1 hour in some cases.

Note: modern precision instruments will be sampling at 16 times a second when calculating the logged results to ensure all the sound levels are included.

Loudness

: Loudness is a subjective assessment of a given sound intensity. The unit of loudness level is 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 - see also the B&K 2250 sound analyser.

Low Frequency Noise Rating : LFNR

: sorry we have no experience in this field, we just include it for completeness. If you have current information we would be pleased to hear from you.

Lp : Sound Pressure Level

LPac : Sound Power

Lpeak : Peak Sound Level

LRPI : Residual Pressure Intensity Index

LSEL : Single Event Noise Exposure Level

Lv : Velocity Level

LW : Sound Power Level

L Weighting