**LA10,18h** (UK Government Environmental Noise Definition) is the arithmetic mean noise level in dB(A) exceeded for 10% of
each hour over the period 06:00 - 24:00 hours;

**LA90** is the noise level exceeded for 90% of the measurement period,
A-weighted and calculated by
statistical analysis

**LAn** is the 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 reportingWe also have a full page on statistical noise levels

**LAeq,T** is the notional A-weighted, equivalent continuous sound level which, if it occurred over the same time period, would give the same noise level as the actual varying sound level. The T denotes the time period over which the average is taken, for example LAeq,8h is the equivalent continuous noise level over an 8 hour period

**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

**LAF** ▫
A-weighted,
fast response,
sound level

**LAFmax** ▫
A-weighted,
fast response,
maximum,
sound level, **note: maximum is not peak**

**LAFmin** ▫
A-weighted,
fast response,
minimum,
sound level

**LAS** ▫
A-weighted,
slow response,
sound level

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

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

**Lavg** ▫ average sound level, results may vary due to National exchange rates and threshold levels

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

**Lavg** ▫ 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 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 (day-evening-night) • Levening • Lnight

See also • community noise equivalent level

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.

● Note 1 : the the kind of level is indicated by use of a compound term such as
sound power level or
sound pressure level.

● Note 2 : the 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.

**Levening (evening level)**, is the
A-weighted,
Leq.
sound level, over the 4 hour evening period 1900 - 2300 hours, also known as *evening noise indicator*

**Lg or Log** under logarithm

*Li* ▫ impact sound pressure level

*Li* ▫ sound intensity level

See also other types of averaging

● 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

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

*Lmax* should not be confused with Peak.

*Ln* see also • logarithm

*Ln* see also • normalized impact sound pressure level

**Lnight (night level)**, the
A-weighted, Leq.,
sound level, over the 8 hour night period of 2300 - 0700 hours and is also known as the *night noise indicator* and other terms.

**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

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 a reference sound level of 0 dB - see our decibel calculation and examples page.

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 the IEC Definition of the Decibel and our sound level calculations and examples page

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.

Longitudinal Wave

**Loudness** is subjective, related to the sound pressure level yes, but also subject to the individual listener's hearing, that changes with age and their subjective response to the character of the noise under consideration. The sound level meter is basically a microphone which converts a sound waves into voltages which the meter measures. It is possible to include filter networks in the meter to 'correct' the measurements for an 'agreed' subjective response. However in the early days this complex technology was not available, so the A, B, C and Lin frequency weighting networks were adopted and standardized.

**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.

**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.

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

See also the comments in the frequency weighted sound levels section

L-weighting

**LZ** ▫
Z-weighted,
sound level

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

**LZeq** ▫
Z-weighted,
Leq equivalent 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