What Are Noise Level Meters?
Noise level meters detect noise to protect the living environment and human health.
Noise is considered sensory pollution along with odor and vibration. It imposes sensory and psychological burdens. Noise includes automobile noise, aircraft noise, bullet train noise, conventional rail line noise, infrasound, and general environmental noise.
Uses of Noise Level Meters
Environmental standards for noise are mainly divided into three categories. In addition, there are two other categories of applicable areas, and one standard value is set as a special exception.
First, Category AA is a type of area that includes areas where noise is required, in areas where medical treatment facilities, social welfare facilities, etc. are clustered together. The standard values are divided into daytime and nighttime, with the former set at 50 decibels or fewer and the latter at 40 decibels or fewer.
Second, there are two categories, A and B. A is for areas used exclusively for residential purposes, and B is for areas used primarily for residential purposes. The standard is set at 55 decibels or fewer during the daytime and 45 decibels or fewer at night.
The third is Category C, which includes areas used for commercial and industrial purposes, in addition to a significant number of residences.
Other applicable areas include, areas fronting on roads with two or more lanes; areas fronting on roads with two or more lanes; and areas fronting on roads with two or more lanes. The former is 60 decibels or lower during the daytime and 55 decibels or lower at night. The latter is 65 decibels or fewer during the day and 60 decibels or fewer at night.
As a special exception, in the case of a strip of roadway with a certain width necessary for the safe and smooth running of vehicles in a single abreast, the standard value is 70 decibels or fewer during the daytime and 65 decibels or fewer during the nighttime in the space adjacent to a road carrying arterial traffic.
However, in the case of individual residences where windows on noise-sensitive surfaces are closed, the standard for noise transmitted indoors is 45 decibels or fewer during the daytime and 40 decibels or fewer at night.
Principles of Noise Level Meters
The first step is to determine the location of the microphone. The microphone should be located where it can avoid the influence of local shielding or reflection by moats, buildings, etc., to grasp the wide area and overall noise situation of the area.
Next, the height of the measurement point should be set at the average height of living surfaces, such as houses in the area.
As for the setting of the dynamic characteristic of the sound level meter, the time weighting characteristic is set as F characteristic, and when only the equivalent noise level is measured, either F characteristic or S characteristic setting is acceptable.
Finally, as for the processing of the sound to be excluded, when the sound to be excluded occurs by dividing the measured time into small segments during the analysis, the statistical processing is performed, excluding the data of the time segment. Sounds to be excluded include natural sounds that are not normal, artificial sounds that do not normally occur, and additional sounds caused by measurements.