**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;

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

We also have a full page on statistical noise levels

**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

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

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 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.

● 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.

See also • Lday • Lden • Lnight

**Lg or Log** under logarithm

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 the Peak.

*Ln* see also logarithm

*Ln* see also normalized impact sound pressure level

See also • Lday • Lden (day -evening-night) • Levening

**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 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 decibel calculations

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

● 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 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