The ear transforms sound pressures in auditory sensations. The hearing spectrum is the range of frequencies which the human ear can hear. It is understood between 20 and 20,000 Hz, although it is more sensitive to frequencies between 2,000 and 5,000 Hz. The sensations that produce sound waves in the ear depend on various physical factors: intensity and the frequency of the wave, the acoustics of the place and the time of day, the sensitivity of people or the type of noise. The noisy environment of the cities is usually produced by multiple sources of both technological source emission as habits and human behaviors that leads to seek solutions to isolate the noise. The car transport, machinery for public works, the agglomeration of people, shopping malls, etc.

are the source of some of the noise in the city. The level of sound or noise can be measured with different computers that measure sound pressure levels, i.e. the variation of pressure that occurs at a particular point when a wave is spreading sound so determine the measurements of the noise. The unit with which this magnitude is expressed is the decibel (dB) and the most widely used measuring equipment is the sound level meter designed to respond to the sound in the same way that the human ear does. The human ear does not equal sensitivity to all audible frequencies, but it sounds of different frequencies but of equal sound pressure level, provoke different sensations. For this reason, the measuring equipment were introduced in weighting curves, being the most used A (dBA). A decibel scale values range from 0 dBA, which is the minimum value that people are able to hear up to 120 or 140 dBA, which correspond to the thresholds of pain and damage to the organ of hearing.

The limit of tolerance or acceptability of the environmental noise level is 65 dBA. The unit of measure used for the environmental sound levels is the level sound continuous equivalent (Leq), which takes into account the variation of noise in a certain period of time, giving a data representative of that period and thus proceed to draw up noise maps. An important aspect for the protection of the urban environment is the classification of the territory into acoustic areas according to the different uses of the soil. In this sense, the municipal Ordinance on noise pollution from the city of Madrid (2) defines five acoustic areas and limits sound levels environmental daytime and nighttime of these areas. Mapping of noise in the municipalities allow you to control noise and noise pollution in a certain area to assess and adopt action plans and remedial measures in that area. Original author and source of the article

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