Gracey & Associates
Noise and Vibration Glossary - E
GLOSSARY INDEX: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
E : Sound Energy density .
E : Sound Exposure .
Ear Simulator : Artificial Ear
Early Decay Time : EDT : is derived from the reverberation time decay curve - the section between 0 dB and 10 dB below the initial level. As it relates to the initial and highest level part of the decaying energy, it is therefore the parameter that relates most to modulation reduction.
Effective Perceived Noise Level : EPNL : a complex rating used to certify aircraft types for flyover noise, based on the PNL - perceived noise level. Includes corrections for pure tones and for the duration of the noise.
Energy : J : = force x distance = work, a quantity equivalent to the capacity of a physical system to do work; the SI unit of energy is the same as the unit of work - the joule J
1 J = 1 N·m = 1 kg·m2/s2 = 1 W·s = 107 ergs
See also sound energy .
Energy Density : E : is the energy per unit volume - J/m3 = W·s/m3.
See also sound energy density .
Energy Density Level : sound energy density level.
Energy Flux : S : Joule/s or watt - see also sound energy flux.
Energy Spectral Density : ESD : the energy spectral density describes how the energy of a signal or a time series is distributed with frequency.
Engineering Units : EU : the units in which a measurement is made; for instance velocity may be expressed in millimetres per second, feet per second, miles per hour, etc., depending on the use to which the data will be put. Some instruments enable you to specify what the engineering units are and to apply conversion factors if needed.
Ensemble Averaging there are two ways to create an average or sample mean. Firstly take the numbers for ten components at any one time (i.e. a vertical column) add them and divide by ten. This is known as the Ensemble Average. Or take one component and average the levels at ten different times, which produces the Time Average. Conventionally the ensemble average is written E(x) and the time average is indicated by putting a bar over the x.
EPNL : Effective Perceived Noise Level
Equal Loudness Contours : 0 dB is the threshold of hearing at 1 kHz. However we are less sensitive at low and high frequencies, so the SPL at 10 Hz, for example would have to be increased to 70 dB for the sound to be just detectable, or of equal loudness - the unit is the phon - see also the Fletcher Munson curves.
Equivalent Continuous Sound Level : LAeq : a steady state dB(A) level which would produce the same A-weighted sound energy over a stated period of time when using a 3 dB exchange rate. It is defined as the A-weighted sound pressure level of a noise fluctuating over a period of time T, expressed as the amount of average energy. Sometimes also known as the LAT - time averaged level
Leq is widely used around the world as a noise index so we include more details here.
ESD : Energy Spectral Density
EU : Engineering Units.
eVDV : Estimated Vibration Dose Value : the whole body Vibration Dose Value is the integrated fourth power vibration value with units m/s1.75. The result is only obtained at the end of the measurement, sometimes 8 or more hours. The eVDV - Estimated Vibration Dose values uses an alternative formulae which enables the VDV to be estimated from early on in the measurement.
Evening Noise Indicator: Levening : EU defined for describing the annoyance due to environmental noise, based on the LAeq measured over the evening period 19.00 to 23.00. See also Lday, Lnight, Lden.
Exchange Rate : Q : is the increase in noise level that corresponds to a doubling of the noise level.
LAeq is always based on an Exchange Rate = 3. Using the 3 dB exchange rate, the 8 hour average level is known LEP,d or LEX,8h. The sound exposure (in physical units) for the measurement duration is known as E (Pa².h)
In America the exchange rate defined in the OSHA standard is 5 dB. Using the 5 dB exchange rate, the 8 hour average level is known as TWA - time weighted average . For other US exchange rates the average level for the measurement duration is known as Lavg
Exponential : a decaying exponential weighting function, specified by a starting point (shift) and a constant time (length). Use exponential weighting for exponentially decaying transients longer than one time record, to avoid leakage caused by truncation.
Exponential Averaging : generates a continuous running average where the most recently sampled spectra have more influence on the average than older ones. This provides a convenient form to examine changing data with the benefit of some averaging to smooth the spectra - see also linear averaging .
Exposure Time : is the actual time that a person is exposed to noise during a workday - used for calculation of Lep,d - daily exposure level.
External Sampling : where a time record capture is triggered by an external signal.
GLOSSARY INDEX: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
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