A-Z list of terminology commonly used within acoustics.
Ear defenders or ear protectors: earmuffs or earplugs worn to provide attenuation of sounds reaching the ear and reduce the risk of noise induced hearing loss.
Early sound reflections (or early sound): reflections of sound from surfaces in a room, which arrive at the receiver within a certain time after the direct sound. This is usually considered too be around 50 ms for speech or about 80 ms for music. Early sound is treated by the listener‚Äôs ear/brain system as being helpful in reinforcing the direct sound signal and therefore acoustic designers will seek to encourage the production of early sound reflections while discouraging late reflections, which produce an unfavorable response in the listener.
Echo: a sound reflection whose magnitude and time delay are such that it is perceived as a separate, distinguishable repetition of the direct sound, as opposed to reverberation, which is perceived as part of the original sound.
Electret or prepolarised microphone: a type of condenser microphone in which a prepolarised layer of electret polymer is used as a dielectric between the diaphragm and backing-plate, which form the condenser.
Electrostatic actuator: a device, which fits over a microphone, close to the diaphragm, and is used for remote calibration.
Emission: a measure of sound energy produced by a source of sound and radiated into the environment (see also immission).
EPNdB (effective perceived noise decibel): a metric used internationally in the noise certification of aircraft.
Equal loudness contours: a standardized set of curves which show how the loudness of pure tone sounds varies with frequency at various sound pressure levels.
Equivalent continuous noise level: see under continuous equivalent noise level, LAeq.
Environmental noise: the European Environmental Noise Directive 2002/49/EC defines environmental noise as ‚Äòunwanted or harmful outdoor sound created by human activities, including noise emitted by means of transport, road traffic, rail traffic, air traffic, and from sites of industrial activity‚Äô.
Eustachian tube: the passage from the middle ear to the back of the throat, which serves to equalize the pressure across the eardrum.
eVDV: estimated vibration dose value; a measure of a cumulative amount of vibration based upon weighted RMS acceleration values and durations; for signals of limited crest facto, the eVDV approximates to the vibration dose value, VDV; see also under root mean quad and vibration dose value.
Eyring‚Äôs formula: a modified version of Sabine‚Äôs formula, for reverberation time, which takes into account the discrete nature of sound reflections; also known as he Norris-Eyring formula.
Exposure limit value: a noise exposure level defined in the 2005 Control of Noise at Work Regulations requiring action from employers (a personal daily (or weekly) noise exposure level of 87 dBA or peak sound pressure level of 140 dBC).