Introduction to the working principle of the sound level meter
The sound is converted into an electrical signal by the microphone, and then the impedance is transformed by the preamplifier to match the microphone with the attenuator. The amplifier adds the output signal to the weighting network, performs frequency weighting on the signal (or an external filter), and then amplifies the signal to a certain amplitude through the attenuator and the amplifier, and sends it to the RMS detector (or an external circuit filter) Level recorder), the numerical value of noise sound level is given on the indicator head.
In order to simulate the different sensitivities of human hearing at different frequencies (20Hz-20KHz), a sound level meter is equipped with a network that can simulate the auditory characteristics of the human ear and correct the electrical signal to an approximate value of the sense of hearing. called weighted network.
The sound pressure level measured through the weighting network is no longer the sound pressure level of the objective physical quantity (called linear sound pressure level), but the sound pressure level corrected by the sense of hearing, called the weighted sound level or noise level.
Since human ears have different perceptions of noise in different frequency bands, they are most sensitive to mid-frequency around 3kHz, and less sensitive to low and high frequencies. good fit. How to unify the measured value with the subjective sense of hearing? So there is an equalization network, or a weighting network, which moderately attenuates both low frequency and high frequency, so that the intermediate frequency is more prominent.
This weighting network is connected between the equipment under test and the measuring instrument, so the influence of the equipment's mid-frequency noise will be "amplified" by the network. In other words, the mid-frequency noise that has the greatest impact on the sense of hearing is given a higher weight. The signal-to-noise ratio measured at the time is called the weighted signal-to-noise ratio, which can more truly reflect people's subjective sense of hearing.
