Glossary
hertz (Hz) The unit of measure for frequency. One hertz is equal to one cycle per second.
insertion loss (IL) The difference in sound pressure measured in a single location, with and without a noise control device (installed between the source and receiver) in place.
near field The area adjacent to the source where sound does not behave as it would in a free field, due to the fact that the source does not radiate sound equally in all directions.
NEBB National Environmental Balancing Bureau (www.nebb.org)
noise Unwanted or obtrusive sound. Generally, people object to sound when it interferes with speech, concentration, or sleep.
noise criteria (NC) A single number used to describe sound in a room. It uses a series of curves for plotting sound pressure by octave band and determining the NC value.
noise reduction (NR) A term used to measure the effect of a barrier on reducing the amount of transmitted sound. It is the difference between sound- pressure measurements taken on each side of a barrier.
noise reduction coefficient (NRC) A single number used to describe the
octave band A range of frequencies that is defined such that the highest frequency in the band is two times the lowest frequency. The octave band is identified by its center frequency.
phon A unit of measure, using a logarithmic scale, used to describe the loudness of a sound.
pitch A subjective quantity used to describe a sound. It is primarily based on frequency, but is also dependent on
receiver sound correction The relationship between the sound energy (sound power) entering the room and the sound pressure at a given point in the room where the receiver hears the sound. This reduction is due to a combination of effects, including distance and the absorptive and reflective properties of the surrounding surfaces. Also called room effect.
reflected sound The sound that bounces off, or is reflected by, a barrier back toward the source.
regenerated sound The noise caused by turbulent flow in air and water systems.
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