Electrostatic Actuator : device comprising an auxiliary electrode that permits the application of an electrostatic force to the metallic or metallized diaphragm of a microphone in order to obtain a calibration.
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 mean sample. Firstly take the values 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, to 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.
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.
Every time the Sound Energy doubles the measured dB level increases by 3 dB, i.e. the exchange rate Q = 3. 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.
Sound Exposure and Noise Dose follow the same rule - a doubling of the level results in a 3 dB increase. However they are also both time dependent. So if the exposure time is doubled the total sound exposure increases by 3dB. Similarly if the Noise Dose was 100%, then doubling the exposure time results in a total noise dose of 200%.
Leq in the UK, Europe and many other places is also based on the Exchange Rate = 3, and the 8 hour working day level is known as the
LEP,d or LEX,8h.
In America, the exchange rate defined in the OSHA standard is 5 dB and their 8 hour workplace average level is known as TWA - Time Weighted Average. For other US Exchange Rates and Threshold Levels the average level for the measurement duration is known as Lavg.
Excitation : external force, or other input, applied to a system.
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 levels have more influence on the average than older samples. This provides a convenient form to examine rapidly changing data with the benefit of some averaging to smooth the spectra.