Glossary of Terms

ACOUSTICS
The science and technology of sound

AMBIENT NOISE
Background noise associated with a given environment. Typically a composite of sounds from many sources located both near and far. No particular sound is dominant.

ANR
Active Noise Reduction, an electronic method of canceling noise.

ANSI
American National Standards Institute.

ATTENUATION
Reduction of sound pressure level as in "hearing protector attenuation"

AUDIOGRAM
A chart showing a person's hearing ability over a range of frequencies.

AUDIOMETER
An instrument used to measure a person's hearing ability.

A-WEIGHTING
A noise measurement that has been corrected to reflect the way a human would hear it. A-weighted measurements also better indicate the potential damage a noise might cause to our hearing.

CEN
Comité Européen de Normalisation (European Committee for Standardisation).

C-WEIGHTING
A filter characteristic that discriminates against very low and very high frequency sounds. Sound levels measured with this filter are designated dB(C).

DECIBEL (dB)
A term representing the ratio of two quantities, one being the sound level that is measured and the other being a reference sound level corresponding approximately to the faintest sounds detectable by the human ear. The greater the sound level measured in dB, the louder is the sound. Generally, a change of 2dB is just perceptible, 5dB is clearly audible, and 10dB appears twice as loud.

EN 352
European Standard specification for industrial hearing protectors.
Part 1: Ear-muffs
Part 2: Ear-plugs
Part 3: Helmet mounted muffs
Part 4: Level dependant muffs
Part 5: ANR muffs
Part 6: Muffs with electrical audio input
Part 7: Level dependant ear-plugs
Part 8: Muffs with entertainment audio input
Part 9: Ear-plugs with electrical audio input
Part 10: Ear-plugs with entertainment audio input.

FREQUENCY
Refers to a periodic or cyclically occurring phenomenon such as a sound wave. Its frequency is the number of times it repeats in one second i.e., cycles per second. The unit of frequency is the Hertz (Hz) which corresponds to 1 cycle per second.

H, M, L
An indication of the attenuation a hearing protector will provide in High, Medium and Low frequency biased noise environments.

HERTZ
See FREQUENCY

k
Prefix indicating multiplication by 1,000, i.e. 1 kHz equals 1,000Hz.

LEP,d
Daily personal noise exposure. The average noise energy a person is exposed to for a working day. The level is usually normalised to the equivalent for 8 hours.

Leq
Equivalent continuous sound pressure. A measure of the average sound pressure level during a period of time.

NOISE
Generally defined as unwanted sound.

NOISE REDUCTION RATING (NRR)
The US EPA method of combining hearing protector attenuation and standard deviation data at many frequencies into a single number measure of hearing protector noise reduction. The NRR represents the approximate dB(A) noise reduction afforded by the protector. The NRR is subtracted from a C-WEIGHTED sound level, i.e. dB(C) (noise level)-NRR=dB(A) (effective exposure).

OCTAVE BAND ANALYSIS
An analysis of noise levels or attenuation into bands one octave apart. The minimum required in Europe is the figures for 125, 250, 500, 1000, 2000, 4000 and 8000 hertz.

PINK NOISE
Random noise with energy distributed equally over the audio frequency range such that there is an equal sound pressure level in each octave band.

PURE TONE
A sound wave consisting of energy at only one single frequency.

SNR
Simplified Noise Reduction also known as Single Number Rating. A single number indicating the attenuation a hearing protector might provide.

SOUND
Variations in pressure in an elastic medium, such as air, which are capable of stimulating the sensation of hearing.

STANDARD DEVIATION
A measure of the variability of a set of data points about their mean (average level). The above terms are frequently used in discussions on hearing protection and hearing conservation.

THRESHOLD OF HEARING
The lowest level of sound that is audible to the human ear