The working principle of the sound level meter is detailed
The microphone converts sound into electrical signals, and then the preamplifier transforms impedance to match the microphone with the attenuator. The amplifier adds the output signal to the weighting network, performs frequency weighting (or external filter) on the signal, and then amplifies the signal to a certain amplitude through an attenuator and amplifier, and sends it to the effective value detector (or external level recorder). The noise level value is given on the indicator head.
In order to simulate the different sensitivities of human auditory perception at different frequencies (20Hz-20KHz), a network is installed in the sound level meter that can simulate the auditory characteristics of the human ear and correct the electrical signal to approximate the auditory perception. This network is called a weighted network.
The sound pressure level measured through a weighted network is no longer an objective physical quantity (called linear sound pressure level), but a sound pressure level corrected by auditory perception, called weighted sound level or noise level.
Due to the varying perceptual abilities of the human ear towards noise in various frequency bands, it is most sensitive to intermediate frequencies around 3kHz, but slightly less sensitive to low and high frequencies. Therefore, regardless of weight, the signal-to-noise ratio may not necessarily be in good agreement with the subjective perception of noise size by the human ear. How to unify measurement values with subjective auditory perception? So there is a balanced network, or weighted network, which moderately attenuates both low and high frequencies, making the mid frequency more prominent.
By connecting this weighted network between the tested equipment and the measuring instrument, the impact of intermediate frequency noise in the equipment will be "amplified" by the network. In other words, the intermediate frequency noise that has the greatest impact on the listening sensation is given higher weights. At this time, the measured signal-to-noise ratio is called the weighted signal-to-noise ratio, which can more realistically reflect the subjective listening sensation of people.
