Measurements in accordance to ISO 1996
The ISO 1996 standards series describe assessment of noise in community environments. The methods and procedures are intended to be applicable to noise from various sources taking into consideration short-time measurements as well as continuous noise monitoring.
Sounds from single events (such as the pass-by of a truck or fly-by of an aircraft) are examples of single-event sounds. To describe such events ISO 1996 recommends to use sound exposure levels (LAE), the maximum sound pressure level (LAmax) and peak sound pressure level (LCpeak). The duration of an event is usually considered as the total time that the sound pressure level is within 10 dB of its maximum sound pressure level.
Various noise sources such as transformers or cooling towers produce continuous sound. To describe continuous sound the equivalent sound pressure level over a time interval is used (LAeq). For intermittent of fluctuating sounds, the LAmax is also used.
Importance of selection of the measurement site is emphasised in ISO 1996-2: 2017 which states that sites for measuring microphones shall be chosen to minimize the effect of residual sound from non-relevant sound sources. The location of the site is critical in obtaining accurate and useful data. The selection of measurement sites should be considered in the early development of a measurement plan once objectives for the measuring system have been clearly identified.
Usually the microphone is mounted on a height of 4 meters during outdoor measurements with a distance of 2 m from reflecting surfaces. In case the microphone is located closer than 2 m from a reflecting surface the appropriate correction to get free field results is applied (e.g. for 0.5-2 m the correction is 3 dB). The station should measure and store sound pressure levels with 1s or less time-averaged intervals together with meteorological data. The measurement data should have an accurate time-stamp. In case of noise monitoring it is essential that system detects noise events using various triggers.
The monitor – instrumentation used for continuous noise monitoring which measures the A-weighted sound pressure levels and their spectra.
Automated sound monitoring system including noise monitoring station, the data post-processing software and hardware peripherals involved in its operation.
The module measuring all relevant meteorological quantities such as wind speed, wind direction, rain, humidity, atmospheric pressure, ect.
SvanNET is a cloud solution providing the on-line access to measurement data and reporting tools.
The instruments for measuring environmental noise shall meet the requirements for a class 1 instrument according to IEC 61672-1 and octave filters shall meet IEC 61260, Class 1. For long-term monitoring the monitoring station should be equipped in automatic system check. For both long-term and short-term measurements, meteorological parameters shall be measured. As a minimum requirement, wind speed, wind direction, relative humidity and temperature shall be measured.
As a part of the monitoring system, SvanPC++ software helps to analyse the measurement results for example to extract and verify noise events such as vehicle pass-bys (car, train, aircraft) with the use of audio recording and automatic event markers.
The ISO recommends that monitoring station is tested and calibrated by the ISO/IEC 17025 laboratory once in a year.
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