NOISE RATING (NR)
A method for rating the acceptability of indoor environments for the purposes of hearing preservation, speech communication and annoyance, based on curves developed by Kosten and van Os (1962).
SOUND PRESSURE LEVELs measured in octave bands are compared with these curves from which a noise rating (NR) is obtained. It will be seen that higher frequencies (where the ear is more sensitive) are given heavier noise ratings than lower ones, information not taken into consideration in strict DECIBEL measurements.
Compare: EQUAL LOUDNESS CONTOURS, SOUND LEVEL, SOUND LEVEL METER.
Acceptable NR values for various environmental situations have also been obtained, along with correction factors for variations.
Compare: COMMUNITY NOISE EQUIVALENT LEVEL, NOISE AND NUMBER INDEX, NOISE CRITERION, NOISE EXPOSURE FORECAST, NOISE LEVEL, NOISE POLLUTION LEVEL, PERCEIVED NOISE LEVEL, SPEECH COMMUNICATION CRITERION, SPEECH INTERFERENCE LEVEL.
Noise rating curves. The individual noise rating (NR) curves are identified by the numerals along the 1000 Hz line (from Kosten and van Os, "Community reaction criteria for external noises," National Physical Laboratory Symposium, No. 12, 1962, p. 377, London H.M.S.O., used by permission).
Area Criterion Correction for dwellings Correction in dB
Pure tone, easily perceptible
Concert hall, legitimate theatre, 500 seats
Impulsive and/or intermittent
Classroom, music room, TV studio, conference room
Noise only during working hours
Sleeping room (see corrections at right)
Noise during 25% of the time
Conference room, 20 seats or with public address system; cinema, hospital, church, courtroom, library
Noise during 6% of the time
Living room (see corrections at right)
Noise during 1.5% of the time
Noise during 0.5% of the time
Noise during 0.1% of the time
Noise during 0.02% of the time
Very quiet suburban
Urban, near some industry
Area of heavy industry