Help Topics - L

Lavg

The logarithmic time average level with an exchange rate of 3, 4, 5 or 6 dB that represents the amount of noise as a single number compared to the actual varying sound level over a specified period of time. When Q = 3 the average level is called the Leq. When Q = 4 the average level is called the LDoD. When Q = 5 the average level is called the LOSHA. For a perfectly steady instantaneous noise level the values of the average levels with different Q factors will be the same.

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LEP,d

LEP,d = Leq(t) + 10 log(10) t/8 hours

The daily personal noise exposure level as specified in European noise at work regulations. It is a measurement of the total time of exposure to noise in the workplace expressed as a constant notional equivalent 8 hour value.

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Leq

The equivalent continuous noise level over a specified period of time that represents the same energy as the actual time varying noise signal. This is a specific form of the time average level when the exchange rate Q is set at a value of 3 dB.

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Level

A descriptor applied to a unit of measurement of sound (or vibration) that denotes the physical quantity is a logarithmic representation of the underlying phenomenon. The decibel is normally used to denote that the value should be referred to as a level rather than the true physical quantity. The most used such value is the ‘A’ weighted sound pressure level expressed as a dB value.

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Level recorder

A device that records the changing noise levels over a period of time to allow the user to see the temporal variations that occurred during the period of interest. High speed paper recorders were often used before the advent of digital data logging in some of the more advanced sound level meters. Time histories can be recorded with multi parameters as fast as every 10 milli seconds with certain newer instruments.

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Linear noise level

The noise level in dB measured without using the 'A', 'C' or any other specified frequency weighting in a sound level meter. The linear frequency response can cover different frequency ranges depending on the quality of the microphone used in the measurement chain. The 'Z' weighting has replaced the linear weighting in more modern noise level meters.

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Liquid crystal display

A type of readout for the display of a sound level meter or noise dosimeter in which the values are shown on a matrix composed of a series of segments. The segments can be custom designed for a particular instrument such as the CEL noise dosimeters or it can be made up of a rows and columns of small dots that are used to form the characters such as in the CEL sound level meters. It is possible to mimic the characteristics of traditional analog displays to indicate the instantaneous level with the advantage that more than a single level can be shown in a small screen area.

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LN%

The notional steady level of noise exceeded for a specified percentage of the total measurement time. The value is usually found from the cumulative distribution table and so the number of sample bins used to collect the raw data in the instrument controls the resolution. For samples collected at 0.5 dB sample resolution the percentile level can only be displayed with a resolution of 0.5 dB. Typically an instrument will be able to calculate and display up to 5 LN% values but other values may be possible to obtain if the distribution table is available at download time using computer software.

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Logarithm

The exponent that indicates the power to which a number must be raised to produce a given number. For the base 10 logarithms as used in acoustics and the study of sound the logarithm of 100 is 2, while the logarithm of 1000 is 3, etc.

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Loudness

The subjective judgment of the intensity of sound by the human hearing mechanism. Loudness depends on the sound pressure and frequency of the stimulus signal. Over the normal audio range it takes about a three fold increase in sound pressure (a ten fold increase of the energy level) to produce a doubling of the impression of loudness.

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Loudness level

This is the measured level in phons and is numerically equivalent to the median sound pressure level of a free progressive 1,000 Hz wave presented to listeners facing the source, which in a number of trials is judged by the listeners to be equally loud.

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Ltm3

The taktmaximal-3 level is a time average value calculated every 3 seconds based taking the highest level occurring during the preceding three seconds and assuming that it was present for the whole of the 3 second interval. This is repeated every 3 seconds to produce a long term average level that will be higher than the equivalent continuous noise level, or Leq, depending on the impulsiveness of the sound under investigation. Comparison of the Ltm3 and the Leq will therefore give an objective measure of the impulsive nature of the noise when assessing nuisance or risk to hearing from high noise levels.

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Ltm5

The taktmaximal-5 level is a time average value calculated every 5 seconds based taking the highest level occurring during the preceding five seconds and assuming that it was present for the whole of the 5 second interval. This is repeated every 5 seconds to produce a long term average level that will be higher than the equivalent continuous noise level, or Leq, depending on the impulsiveness of the sound under investigation. Comparison of the Ltm5 and the Leq will therefore give an objective measure of the impulsive nature of the noise when assessing nuisance or risk to hearing from high noise levels.

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