**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.

**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.

**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 level •
community 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 Lday • Lden • Levening • Lnight.

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

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

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

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

**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.

**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

**LCS** :
C-weighted,
slow response,
sound level

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

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

See also Lden • Levening • Lnight

See also CNEL - community noise equivalent level • Lday • Levening • Lnight

**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.

Level DefinitionIEC 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 difference • sound energy level • sound exposure level • sound intensity level • sound level • sound power level • sound pressure level

See also Lday • Lden • Lnight.

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 propagation • elementary dephasing of sound propagation • elementary exponent of sound propagation • propagation loss definition

**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

See also inverse square law

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

See also constant bandwidth • constant percentage bandwidths • continuous spectrum • fast fourier transform • narrowband noise • narrowband spectra • octave bands. pink noise • white noise • wideband noise

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

**Lmax should not be confused with ** Peak.

**Ln** : normalized impact sound pressure levels - sound insulation, laboratory measurements.

**L'n** : normalized impact sound pressure levels - sound insulation, field measurements

See also Lday • Lden • Levening

**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

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

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

Note : modern precision instruments sample at 16 times a second to ensure all the sound levels are included.

Longitudinal Wave

**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 level • equal loudness contours • fletcher munson curves • methods for calculating loudness • minimum audible field

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

**Lpt** : tone assessment parameter

**Lpti** : tone assessment parameter

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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