The Noise Rating NR - Curve determine the acceptable indoor environment for hearing preservation, speech communication and annoyance according to the ISO 1973. This is done by measuring the specify background noise in unoccupied buildings and spaces.
In most cases, the goal is that background noise should not interfere with the purpose of the room, for example, the noise of an office air-conditioning system and consistent noise of traffic outside the building should not interfere with phone calls or conversations. Background noise that is annoying creates fatigue and can negatively affect productivity and safety. Too much noise also affects the ability to communicate.
The noise rating graphs for different sound pressure levels are plotted at acceptable sound pressure levels at different frequencies. Acceptable sound pressure level vary with the room and the use of it. Different curves are obtained for each type of use. Each curve is obtained by a NR number.
Noise rating curves are measured in 1/1 octave bands, typically between 31.5 Hz and 8 kHz.
Norsonic sound level meters for noise rating measurements:
The Nor150, Nor145, Nor140 and Nor131 can be used to measure NR noise rating curves.
On the Nor131 and Nor132 it is even possible to read the NR value directly on the instrument display.