E : Sound and Vibration Terms, Definitions, Units, Measurements ...
Early Decay Time (EDT)
is derived from the
decay curve; 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 milliseconds integrate with the direct sound and can improve speech clarity - see the Haas effect.
See also • Schroeder
EAV • exposure action value
Echo, sound waves are reflected by walls and other hard surfaces and if the arrival of the reflected wave is delayed by more than 25 milliseconds, see the Haas effect, then the delayed sound is noticeable and called an echo. When a sound wave experiences multiple reflections this is known as reverberation
sound wave that has been reflected and arrives with such a magnitude and time interval after the direct sound as to be distinguishable as a repetition of it.
• flutter echo
• multiple echo
Effective Sound Intensity
Effective Sound Pressure
Elastic Medium, a term used when discussing sound waves, where the particles in the medium 'assist' the transmission of the wave but then return to their 'original' state, i.e. no net movement, also known as elastic wave
Electret Microphones are widely used in noise measurements because they offer the good linearity, wide frequency range and high stability.
Because of their importance in acoustics, we include more details, see measurement microphones
Electrostatic Actuator Definition IEC 801-28-10, 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.
Elementary Exponent of Sound Propagation Definition IEC 801-23-34, with respect to a system having a periodic structure, the natural logarithm of the complex ratio of particle velocities (or pressures) measured at two successive corresponding points of the structure, when this structure is assumed to be of infinite length
ELV • exposure limit value
Energy (J) = force x distance = work, a scalar quantity equivalent to the capacity of a physical system to do work; the SI unit of energy is the Joule (J).
for a system of particles and fields, set of states associated with a specified energy
● Note 1 : this concept is particularly useful when energy changes by quanta.
● Note 2 : the term energy level is also used for the associated energy.
See also • sound energy
Energy Density is the amount of energy stored in a given system or region of space per unit volume, the SI Units are J/m3
See also • sound energy density
Energy Flux is the rate of transfer of energy.
In the case of energy transfer per unit area, also known as energy flux density, the SI units are W/m2 and sound energy flux is in this category.
In the case of total rate of energy transfer, the SI unit is the Watt (W).
See also • sound energy flux
Energy Spectral Density (ESD)
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.
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 other types of averaging
EPA - Environmental Protection Agency (USA)
EPNdB • effective perceived noise level
EPNL • effective perceived noise level
Equal Loudness Contours have been arrived at by group consensus. 0 dB is the threshold of hearing at 1 kHz. However we are less sensitive at low and high frequencies, so the sound pressure level 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.
Equal Loudness Contour Definition IEC 801-29-08, curve that shows, as a function of frequency, the sound pressure level required to cause a given loudness for a listener having normal hearing, when listening to a specified kind of sound in a specified manner.
See also • BS ISO 226 Equal-loudness contours
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.
A stable situation in which all the forces cancel on another.
Equivalent Acceleration (Aeq, Aeq4, Aeq8)
Equivalent Continuous Sound Level Definition IEC 801-22-16, logarithm of the ratio of a given time-mean-square, standard-frequency-weighted sound pressure for a stated time period, to the square of the reference sound pressure of 20 μPa. Time-average sound level in decibels is 10 times the logarithm to the base ten of that ratio, also known as the time-averaged sound level and the LAeq.
Note 1 : if a frequency weighting is not specified, the A-frequency weighting is understood.
Note 2 : in principle, exponential time weighting is not involved.
Equivalent Continuous Sound Pressure Level Definition IEC 801-22-11, logarithm of the ratio of a given root-mean-square sound pressure, during a stated time interval, to the reference sound pressure. Average sound pressure level in decibels is 20 times the logarithm to the base ten of that ratio and is also known as the time-average sound pressure level
Note : unless otherwise specified, the reference sound pressure for airborne sound is 20 μPa.
Note the fundamental differences between these two definitions
Equivalent Sound Absorption Area
Erg 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 Noise Dose
Estimated Vibration Dose Value
EU • engineering units
eVDV • estimated vibration dose value
Evening Noise Indicator
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 sound level calculations article.
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% of the acceptable daily maximum, then doubling the exposure time results in a total noise dose of 200%, twice the daily limit.
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 time weighted average. For other US exchange rates and threshold levels the average level for the measurement duration is known as Lavg.
external force, or other input, applied to a system, also known as stimulus.
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 other types of averaging
noise dose •
, where a level vs time record is triggered by an external signal.
Glossary Search •
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