Acoustic Glossary


 

L : Sound and Vibration Terms ...


LA : A-weighted, sound level.

LA10 the A-weighted, sound level just exceeded for 10% of the measurement period, calculated by statistical analysis.

LA10,18h (UK Traffic Noise Regulations), the arithmetic mean noise level in dB(A) exceeded for 10% of each hour over the period 06:00 - 24:00 hours.

LA90 the A-weighted, sound level just exceeded for 90% of the measurement period and calculated by statistical analysis.

LA10 and LA90 are extensively used for rating traffic noise and background noise respectively. The measurement period should also be stated. For example, LA10,18h is considered good practice when reporting road traffic noise measurements.

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

See also percentile noise levels.


LAE : A-weighted, sound exposure level.

LAeq : A-weighted, equivalent continuous sound level.

LAeq,T is the A-weighted, equivalent continuous sound level. T denotes the time period over which the fluctuating sound levels were averaged, for example LAeq,8h is the equivalent continuous noise level over an 8 hour period. See also the daily noise exposure levelcommunity noise equivalent level.

LAeq,6h (UK Government Environmental Noise Definition), is the equivalent continuous sound level in dB(A) that, over the period 24:00-06:00 hours, contains the same sound energy as the actual fluctuating sound that occurred in that period.

LAeq,16h (UK Government Environmental Noise Definition), is the equivalent continuous sound level in dB(A) that, over the period 07:00-23:00 hours, contains the same sound energy as the actual fluctuating sound that occurred in that period.

LAeq,18h (UK Government Environmental Noise Definition), is the equivalent continuous sound level in dB(A) that, over the period 06:00-24:00 hours, contains the same sound energy as the actual fluctuating sound that occurred in that period

See also LdayLdenLeveningLnight.


LAF : A-weighted sound level measured with a fast time-constant.

LAFmax : A-weighted maximum sound level measured with a fast time-constant - Note, maximum is not peak

LAFmin : A-weighted minimum sound level measured with a fast time constant


LAIeq : A-weighted, impulse, leq sound level

LAmax : A-weighted, maximum, sound level - note: maximum is not peak

LArT : sound rating level, the a-weighted, leq sound level of an industrial noise during a specified time period, adjusted for tonal character and impulsiveness

LAS : A-weighted, slow time constant response, sound level

LASmax : A-weighted, slow response, maximum, sound level, note : maximum is not peak

LASmin : A-weighted, slow response, minimum, sound level


LAT is the time average sound level, also known as the equivalent continuous sound level.

Lavg is the average sound level, the results may vary due to local exchange rates and threshold levels.

Lavg is the Leq (equivalent continuous sound level) when the exchange rate is 3 and no threshold is set.

Lavg is the TWA (time-weighted average), measured over 8 hours. In Europe and the UK a 3dB exchange rate is always used.


LC : C-weighted, sound level

LCE : C-weighted, sound exposure level

LCeq : C-weighted, Leq (equivalent continuous sound level)

LCF : C-weighted, fast response, sound level

LCFmax : C-weighted, fast response, maximum, sound level - note: maximum is not peak


LCpeak : C-weighted, peak, sound level

LCS : C-weighted, slow response, sound level

LCSmax : C-weighted, slow response, maximum, sound level

LCSmin : C-weighted, slow response, minimum, sound level


Lday : day noise level, the A-weighted, Leq (equivalent noise level), over the 12-hour day period (07:00-19:00), also known as the day noise indicator.

See also LdenLeveningLnight


Lden : day-evening-night noise level, the A-weighted, Leq (equivalent noise level) over a whole day, but with a penalty of 10 dB(A) for night-time noise (23:00-07:00) and 5 dB(A) for evening noise (19:00-23:00), also known as the day evening night noise indicator

See also CNEL - community noise equivalent levelLdayLeveningLnight


Ldn : day-night noise level, the LAeq (equivalent noise level) over a 24 hour period with a penalty of 10 dB(A) for noise during the hours of 23:00-07:00, also known as the day night indicator.

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 or spectral 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 worse for continuous signals and rectangular window, and it is greatly reduced by use of the hanning window, a form of apodization, which forces the signal level to zero at the ends of the data block.

Length a scalar quantity and one of the seven SI base quantities. The SI unit of length is the metre, symbol (m).

LEP,d : daily personal noise exposure level
LEPN : effective perceived noise level - aircraft noise

LEP,w : weekly personal noise exposure

Leq : equivalent continuous sound level

Level Definition IEC 801-22-01, logarithm of the ratio of a given quantity to a reference quantity of the same kind. The base of the logarithm, the reference quantity, and the kind of level must be indicated.
Note 1 : the kind of level is indicated by use of a compound term such as sound power level or sound pressure level.
Note 2 : the value of the reference quantity remains unchanged, whether the chosen quantity is Peak, RMS, or otherwise.
Note 3 : the base of the logarithm is indicated by use of a unit of level associated with that base.

See also level differencesound energy levelsound exposure levelsound intensity levelsound levelsound power levelsound pressure level


Levening : evening noise level, the A-weighted, Leq (equivalent noise level) over the 4 hour evening period 19:00-23:00 hours, also known as evening noise indicator

See also LdayLdenLnight.


LEX,8h : daily noise exposure level

LFNRV : 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 smooths out random noise components in a spectrum.

See also other types of averaging


Linear Exponent of Sound Propagation Definition IEC 801-23-33, with respect to a uniform system, natural logarithm of the complex ratio of particle velocities (or pressures) measured at two successive points separated by unit distance, when this system is assumed to be of infinite length, also known as the sound propagation coefficient

See also elementary attenuation of propagationelementary dephasing of sound propagationelementary exponent of sound propagationpropagation loss definition


Linear Momentum (p) = mass x velocity.

Linear System Definition IEC 351-42-11, system the behaviour of which obeys the principle of superposition.
Note 1 : the principle of superposition implies that such a system may be described by a set of linear equations.
Note 2 : a system, which does not have this property, is called nonlinear system.


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.

See also inverse square law


Line Spacing is the frequency difference between two adjacent 'lines' in a line spectrum

Line Spectrum Definition IEC 801-21-16, sound spectrum containing only discrete frequency components.

See also constant bandwidthconstant percentage bandwidthscontinuous spectrumfast fourier transformnarrowband noisenarrowband spectraoctave bands. pink noisewhite noisewideband noise


Li,R : pressure-residual sound intensity index

Live Room Definition IEC 801-31-14, room characterised by a relatively small amount of sound absorption.


Lk : sound intensity pressure intensity index

Lmax, the maximum sound level, during a measurement period or a noise event, Often includes other descriptors, for example LAFmax, and sometimes written as Max dB(A).

Lmax should not be confused with Peak.


Lmin, the minimum sound level, during a measurement period or a noise event. Often includes other descriptors, for example LAFmin, and sometimes written as Min dB(A).

Ln is the percentile noise level where 'n' is between 0.01 and 99.9%, of the time, calculated by statistical analysis and usually includes a descriptor i.e. A-weighting. The most common Ln values are the LA10, LA90 and LA95 levels.

Ln : normalized impact sound pressure levels - sound insulation, laboratory measurements.
L'n : normalized impact sound pressure levels - sound insulation, field measurements


Lnight : night noise level, the A-weighted, Leq (equivalent noise level) over the 8 hour night period of 23:00 to 07:00 hours, also known as the night noise indicator.

See also LdayLdenLevening


Lnp : noise pollution level

LnT : standardized impact sound pressure level - insulation, laboratory measurements

L'nT : standardized impact sound pressure level - insulation, field measurements

LnT,w : weighted standardized impact sound pressure level - insulation, laboratory measurements

L'nT,w : weighted standardized impact sound pressure level - insulation, field measurements

Ln,w : weighted normalized impact sound pressure level - insulation, laboratory measurements

L'n,w : weighted normalized impact sound pressure level - insulation, field measurements


Localisation, the listener's ability to respond to time and level differences between both ears as well as spectrum information, correlation and pattern matching

See also binaural and our HATS - head and torso sumulator


Logarithm, Log, log, lg, Ln, (common logarithm ratios), expressed in decibels (dB) are widely used in acoustics to convert the immense range we can hear into manageable numbers.
For example we can hear sound power levels of 0.000000000001 watts up to 100 watts or more.
Similarly we can hear sound pressure levels of 0.00002 pascals up to 200 pascals.
Converting these levels into dBs results in a range of values 0 dB up 140 dB - much easier to 'handle'.

The common logarithm is the logarithm to the base 10 and is often written as log10(x) or log (x) but this can be confusing as the "log" on most calculators 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 possible confusion, ISO, the International Standards Organisation, recommend:-
log10(x) should be written lg (x) and
loge(x)   should be written ln (x).

** see our Sound Level Calculations page using online calculators.
See also the IEC Definition of the Decibel and our sound level calculations and examples page


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.

Logarithmic Decrement Definition IEC 801-24-23, natural logarithm of the ratio of any two successive maxima of like sign, in the decay of a single-frequency oscillation.


Logarithmic Frequency Interval Definition IEC 801-30-08, logarithm of the ratio of two frequencies.

See also • frequency interval


Logging is the process of recording the noise data at regular intervals, so a 'picture' of the fluctuations may be studied at the end of a long measurement. Traditionally 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 sample at 16 times a second to ensure all the sound levels are included.

Longitudinal Wave

Loudness depends not only on the sound level(s) and the frequencies involved, but also on the listener's subjective response to the character of the noise under consideration.

Loudness Definition IEC 801-29-03, that attribute of auditory sensation in terms of which sounds may be ordered on a scale extending from soft to loud.
Note : loudness depends primarily upon the sound pressure of the stimulus, but also upon its frequency, waveform and duration.

Loudness Level Definition IEC 801-29-05, of a sound, in phons, numerically equal to the median sound pressure level in decibels, re 20 μPa of a free progressive wave having a frequency of 1,000 Hz presented to listeners having normal hearing facing the source that in a specified number of trials is judged equally as loud as the unknown sound.

See also • calculated loudness levelequal loudness contoursfletcher munson curvesmethods for calculating loudnessminimum audible field

For modern loudness measurements, see the B&K 2250 sound analyser

Low Frequency Noise Rating (LFNR), we have no experience in this specific rating and just include it for completeness. We are aware of the 'proposed criteria' produced for DEFRA by the University of Salford in 2005. If you have current information we would be pleased to hear from you.

See also the comments in the A-weighted sound level entry


Low Pass Filter, signals above the cut-off frequency are attenuated. The attenuation slope is called the roll-off

Lp : sound pressure level

LPac : the sound power

Lpeak and Lpk : peak sound pressure

LPN : perceived noise level

Lpn : tone assessment parameter

Lpt : tone assessment parameter

Lpti : tone assessment parameter


LRPI : pressure residual sound intensity index

LSEL : single event noise exposure level

Lta : tone assessment parameter

Lv : particle velocity level

Lw : sound power level

L-weighting

LZ : Z-weighted, sound level

LZE : Z-weighted, sound exposure level

LZeq : Z-weighted, Leq equivalent continuous sound level

LZF : Z-weighted, fast response, sound level

LZFmax : Z-weighted, fast response, maximum, sound level

LZFmin : Z-weighted, fast response, minimum, sound level

LZS : Z-weighted, slow response, sound level

LZSmax : Z-weighted, slow response, maximum, sound level

LZSmin : Z-weighted, slow response, minimum, sound level

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