Acoustic Glossary


 

E :  Sound and Vibration Definitions, Terms, Units, Measurements ...


Early Decay Time : EDT : is derived from the Reverberation Time decay curve - the section between 0 dB and 10 dB below the initial level.

 

A short EDT is a good indicator of speech clarity as early reflections that reach the listener within 50 ms integrate with the direct sound and can improve speech clarity - see the Haas Effect.


Ear Simulator : Artificial Ear


EAV : Exposure Action Value

Effective : in acoustics more commonly known as the RMS - Root Mean Square of the Instantaneous level over a given period of time.

The shortened suffix eff is also used in formulae for example Peff

Effective Perceived Noise Level
Effective Sound Pressure Level

Electret Microphones : are widely used in noise measurements because they offer the best linearity, frequency range and high stability.

Because of their importance, in acoustics, we include more details on Measurement Microphones


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.


page up
ELV : Exposure Limit Value

Energy : Sound Energy
Energy : Sound Energy Density
Energy : Sound Energy Density Level
Energy : Sound Energy Flux
Energy : Sound Energy Reference Levels
Energy : Sound Energy Spectral Density

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.

see also :
Exponential Averaging
Linear Averaging
RMS Averaging
Spatial Averaging
Spectrum Averaging
Time Domain Averaging

EPNL : Effective Perceived Noise Level


Equilibrium : the state of a body or physical system at rest or in un-accelerated motion in which the resultant of all forces acting on it is zero and the sum of all torques about any axis is zero.


Equal Loudness Contours

Equivalent Constant Acceleration : Aeq, Aeq4, Aeq8
Equivalent Continuous A-weighted Sound Level : LAeq
Equivalent Continuous Sound Level : Leq
Equivalent Sound Absorption Area
Equivalent Sound Pressure Level : Leq

page up

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


ESD : Energy Spectral Density

Estimated Vibration Dose Value : eVDV

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.


eVDV : Estimated Vibration Dose Value


Evening Noise Indicator : Levening


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.


page up

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.

see also : Time Weightings.

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.

see also :
Ensemble Averaging
Linear Averaging
RMS Averaging
Spatial Averaging
Spectrum Averaging
Time Domain Averaging

Exposure : Sound Exposure : see also Noise Dose
Exposure : Acceleration : see also Vibration Dose

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 : Sound Exposure
and : Acceleration : Aeq : Vibration Dose Value - VDV

page up

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 : Sound Exposure
and : Acceleration : Aeq : 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.