**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 noise level)** is the
A-weighted,
Leq (equivalent noise level) over the 4 hour evening period 19:00-23:00 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

See also • elementary attenuation of propagation • elementary dephasing of sound propagation • elementary exponent of sound propagation • propagation loss definition

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

**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 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.

**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