This document may not be reproduced in full or in part without the written consent of Marshall Day Acoustics Limited Rp 001 R0 20210601 SJP (Waihi North Noise Assessment) ISSUE 51 of 79 APPENDIX A GLOSSARY OF TERMINOLOGY Ambient The ambient noise level is the noise level measured in the absence of the intrusive noise or the noise requiring control. Ambient noise levels are frequently measured to determine the situation prior to the addition of a new noise source. A-weighting The process by which noise levels are corrected to account for the non-linear frequency response of the human ear. dB Decibel The unit of sound level. Expressed as a logarithmic ratio of sound pressure P relative to a reference pressure of Pr=20 µPa i.e. dB = 20 x log(P/Pr) LA10 (t) The A-weighted noise level equalled or exceeded for 10% of the measurement period. This is commonly referred to as the average maximum noise level. The suffix "t" represents the time period to which the noise level relates, e.g. (8 h) would represent a period of 8 hours, (15 min) would represent a period of 15 minutes and (2200-0700) would represent a measurement time between 10 pm and 7 am. LA90 (t) The A-weighted noise level equalled or exceeded for 90% of the measurement period. This is commonly referred to as the background noise level. The suffix "t" represents the time period to which the noise level relates, e.g. (8 h) would represent a period of 8 hours, (15 min) would represent a period of 15 minutes and (2200-0700) would represent a measurement time between 10 pm and 7 am. LAeq (t) The equivalent continuous (time-averaged) A-weighted sound level. This is commonly referred to as the average noise level. The suffix "t" represents the time period to which the noise level relates, e.g. (8 h) would represent a period of 8 hours, (15 min) would represent a period of 15 minutes and (2200-0700) would represent a measurement time between 10 pm and 7 am. LAmax The A-weighted maximum noise level. The highest noise level which occurs during the measurement period. Ldn The day night noise level which is calculated from the 24 hour LAeq with a 10 dB penalty applied to the night-time (2200-0700 hours) LAeq. Masking Noise Intentional background noise that is not disturbing, but due to its presence causes other unwanted noises to be less intelligible, noticeable and distracting. Noise A sound that is unwanted by, or distracting to, the receiver. NZS 6801:2008 New Zealand Standard NZS 6801:2008 “Acoustics – Measurement of environmental sound” NZS 6802:2008 New Zealand Standard NZS 6802:2008 “Acoustics – Environmental Noise” NZS 6803:1999 New Zealand Standard NZS 6803: 1999 “Acoustics - Construction Noise” NZS 6806:2010 New Zealand Standard NZS 6806:2010 “Acoustics - Road-traffic noise - New and altered roads” SEL or LAE Sound Exposure Level The sound level of one second duration which has the same amount of energy as the actual noise event measured. Usually used to measure the sound energy of a particular event, such as a train pass-by or an aircraft flyover. Special Audible Characteristics Distinctive characteristics of a sound which are likely to subjectively cause adverse community response at lower levels than a sound without such characteristics. Examples are tonality (e.g. a hum or a whine) and impulsiveness (e.g. bangs or thumps). SPL or LP Sound Pressure Level A logarithmic ratio of a sound pressure measured at distance, relative to the threshold of hearing (20 µPa RMS) and expressed in decibels. SWL or LW Sound Power Level A logarithmic ratio of the acoustic power output of a source relative to 10-12 watts and expressed in decibels. Sound power level is calculated frommeasured sound pressure levels and represents the level of total sound power radiated by a sound source.
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