This last one is not more than the combination of values of electrical and thermal noise that undergoes the 20 microphone to C (expressed in dB). It varies from a type to another one of consideration of frequencies. It is necessary to know, in addition, by which microphones it is possible to interchange the provided one. And, also, the answer of the instrument before infra and ultrasounds, in the case that are of interest. Parameters of measurement: This aspect determines the types of measurements that can take control of the instrument.

The parameters consider two types of considerations, that is to say: Considerations of frequency: they can be To, B, C, D, U.? Considerations of time: they can be S (slow), F (fast), I (impulsive) and Peak (tip). It is significant that all the models of sound level meters do not count on the total of existing considerations. Once again it is made essential to know, not to fail in the election, what is wanted to measure and whereupon ojetivo. Actually, as it is possible to be deduced, it is possible to combine the compensations of time and frequency of the instrument, in dependency of the characteristics of the acoustic event to study. Next it is offered, in tables 1 and 2, a brief characterization of each of them. Table 1. Considerations of Frequency Considerations of frequency Characterization To Are the network of consideration more commonly used for valuation of auditory damage and intelligibility of the word. Employee initially to analyze sounds of low intensity, is today, practically, the reference that use the laws and regulations against the noise produced at any level.

B was created to model the answer of the human ear to average intensities. Nevertheless, at present it is very little used. In fact a great amount of sound level meters contemplates no longer it. C In their origins was created to model the answer of the ear before sounds of great intensity.