L : Sound Level

La : Acceleration Level

**LA** :
A-weighted,
Sound Level.

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

**LA90** : 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** : SEL (sound exposure level) with "A" frequency weighting.

**LAeq** :
A-weighted,
equivalent sound level.
A widely used noise parameter describing a sound level with the same Energy content as the varying acoustic signal measured - also written as dBA Leq. .. more LAeq details

**LAF** :
A-weighted,
fast,
sound level.

**LAFmax** :
A-weighted,
fast,
maximum,
sound level.

**LAFmin** :
A-weighted,
fast,
minimum,
sound level.

**LAIeq** :
A-weighted,
impulse,
leq,
sound level.

**LAmax** :
A-weighted,
maximum,
sound level

**LArT : Sound Rating Level** : the A-weighted, Leq, sound pressure level of an industrial noise during a specified time period, adjusted for tonal character and impulsiveness

**LAS** :
A-weighted,
slow,
sound level.

**LASmax** :
A-weighted,
slow,
maximum,
sound level.

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

LAT : time average sound level

**Lavg** averaged sound level with selectable exchange rate. Results also vary depending if a threshold level was used.

**Lavg** : Leq - equivalent sound level measurements - only when the exchange rate is 3 and the threshold is set to none.

**Lavg** : TWA - time weighted average when the exchange rates and threshold levels are the same and the measurement period was 8 hours.

**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.

Also known as • *Day noise indicator* and other terms.

See also • community noise equivalent level • evening equivalent level

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* 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 worst 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.

**LEP,d :** Daily personal noise exposure

**LEPN :** Effective perceived noise level

**LEP,w :** Weekly personal noise exposure

**Leq :** Equivalent sound level

● 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.

**LEX,8h :** Daily Exposure Level

**LF :** Force level

**LFNR :** Low frequency noise rating

**Lg or Log :** Logarithm

**Li :** Impact sound pressure 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.

See also • other types of averaging

Linear Exponent of Sound Propagation

**Linear Momentum (p)** =
mass x velocity

● 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.

**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 • Point Source

**Line Spacing :** the frequency difference between two adjacent 'lines' in a Line Spectrum

See also • FFT - Fast fourier transform.

*Lmax* should not be confused with the Peak.

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 : Normalized Impact Sound Pressure Level

**Lnight : Night equivalent level :**
Leq.
A-weighted,
sound level, measured overnight 23.00 - 0700 hours.

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

**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

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 reference sound level - see the decibel for a more detailed explanation and practical examples in acoustics.

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 possible confusion, ISO, the International Standards Organisation, recommend:-

log10(x) should be written lg (x) and

loge(x) should be written ln (x).

See also • frequency interval

● 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.

● Note : loudness depends primarily upon the sound pressure of the stimulus, but also upon its frequency, waveform and duration.

See also • calculated loudness level • equal loudness contours • fletcher munson curves • Methods for calculating loudness • minimum audible field

For 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 frequency weighted sound levels section

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

Lp : Sound Pressure Level

LPac : Sound Power

Lpeak (Lpk) : Peak Sound Pressure

Lpn : Tone Assessment parameter

Lpt : Tone Assessment parameter

Lpti : Tone Assessment parameter

LRPI : Residual Pressure Intensity Index

LSEL : Single Event Noise Exposure Level

Lta : Tone Assessment parameter

Lv : Velocity Level

LW : Sound Power Level

L-weighting

**LZ :**
Z-weighted,
sound level.

**LZE :**
Z-weighted,
sound exposure level

**LZeq : **
Z-weighted,
Leq,
sound level.

**LZF : **
Z-weighted,
Fast,
sound level.

** LZFmax : **
Z-weighted,
Fast,
Maximum,
sound level.

**LZFmin : **
Z-weighted,
Fast,
Minimum,
sound level.

**LZS : **
Z-weighted,
Slow,
sound level.

**LZSmax : **
Z-weighted,
Slow,
Maximum,
sound level.

**LZSmin : **
Z-weighted,
Slow,
Minimum,
sound level.

Home • Glossary Search • Certified Instrumentation for Hire