Definitions, Terms, Units and Parameters
E
To find specific terms on a page use CTRL+FEarly 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 Perceived Noise Level - PNL. Includes corrections for pure tones and for the duration of the noise.The EPNL measurement is based on the following equation: EPNL = PNLmax + 10 lg (t10/20) + F (dB)
where PNLmax is the maximum Perceived Noise Level during flyover in PNdB, t10 is the duration in seconds during which the noise level was within 10 dB of the PNLmax and F is a correction for the Pure Tone component, typically 3 dB.
Effective Sound Pressure
: is the rms - root mean square of the instantaneous sound pressure over a given interval of time - see also Sound Pressure.Electret Microphones
: are widely used in noise measurements because they offer the best linearity, frequency range and high stability.Because of their importance we have prepared more details Measurement Microphones
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
: a complex rating used to certify aircraft types for flyover noise, based on the Perceived Noise Level - PNL. Includes corrections for pure tones and for the duration of the noise.The EPNL measurement is based on the following equation: EPNL = PNLmax + 10 lg (t10/20) + F (dB)
where PNLmax is the maximum Perceived Noise Level during flyover in PNdB, t10 is the duration in seconds during which the noise level was within 10 dB of the PNLmax and F is a correction for the Pure Tone component, typically 3 dB.
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 A-weighted Sound Level : LAeq
: the constant sound level that, in a given time period, would convey the same sound energy as the actual time-varying A-weighted sound level.Equivalent Continuous Sound Pressure Level : Leq
: is the preferred single value figure to describe sound pressure levels that vary over time and would produce the same sound energy over the stated period of time T.It is good practice to include other measurement parameters such as A-weighting and the measurement period, for example LAeq,t.
If the Leq is measured over 8 hours then Leq = LEP,d = LEX,8h = %Dose.
Leq is widely used, but not widely understood, so we include more details here.
Sometimes also known as the LAT - time averaged level
See also Short Leq
Also known as the Equivalent Sound Level and Equivalent Noise level
.Erg : erg
: an erg is the amount of work done by a force of one dyne exerted for a distance of one centimetre. In the CGS base units.1 erg = 1 dyne cm = 10-7 Joule
EU : Engineering Units
: 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.Exchange Rate : Q
: is the increase in noise level that corresponds to a doubling of the noise level.Leq 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)
Every time the sound energy doubles the measured dB level increases by 3 dB, this is known as the Exchange Rate : Q. For example if a machine produces 80 dBA then adding another identical machine increases the measured level to 83 dBA. So four identical machines, 4 times the sound energy, would measure 86 dBA, we are adding decibels not numbers. This is explained in detail with examples in our decibels page
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 samples. This provides a convenient form to examine changing data with the benefit of some averaging to smooth the spectra.Other averaging methods : Linear RMS Spatial Spectrum Time Domain
Exposure Action Value : EAV
is an 8-hour daily amount of noise and vibration exposure above which employers are required to take action to control exposure.For noise there are two action levels,:-
♦ the Lower EAV is 80 dBA and a peak sound pressure of 135 dBC
♦ the Upper EAV is 85 dBA and a peak sound pressure level of 137 dBC.
For hand arm vibration the EAV is 2.5 m/s2
For whole body vibration the EAV is 0.5 m/s2
See also Noise Dose l Sound Exposure l Vibration Dose Value - VDV
Exposure Limit Value : ELV
: is the maximum amount of noise and vibration an employee may be exposed to on any single 8-hour day.For noise the daily or weekly exposure is 87 dBA and a peak - sound pressure of 140 dBC.
For hand arm vibration the ELV is 5 m/s2
For whole body vibration the ELV is 1.15 m/s2
See also Noise Dose l Sound Exposure l Vibration Dose Value - VDV
Exposure Time
: the time a person is exposed to noise during a workday - used for calculation of LEP,d - Daily Personal Noise Exposure, see also Noise Dose.External Sampling
: where a time record capture is triggered by an external signal.Page Up l Glossary Search l Certified Instrumentation
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