Weighting network for sound level meters
In order to simulate the human ear hearing at different frequencies have different sensitivity, in the sound level meter has a can simulate the hearing characteristics of the human ear, the electrical signal is corrected to approximate the value of the network with the auditory sense, this network is called the weighting network. The sound pressure level measured by the weighting network is no longer the objective physical sound pressure level (called linear sound pressure level), but the sound pressure level corrected by the sense of hearing, called the weighted sound level or noise level.
A weighted (also called weighted) parameter is a parameter measured after some weighting of the frequency response curve to distinguish it from an unweighted parameter in a flat frequency response state. For example, the signal-to-noise ratio, according to the definition, we measure the noise level under the rated signal level (which can be power, or voltage, current), the ratio of the rated level to the noise level is the signal-to-noise ratio, and if it is a decibel value, the difference between the two is calculated. This is the unweighted signal-to-noise ratio. However, since the human ear is not the same in its ability to perceive noise in all frequency bands, and is *sensitive* to mid-frequencies around 3kHz, but less so to low and high frequencies, the unweighted S/N ratio may not coincide well with the human ear's subjective perception of the size of the noise.
How to harmonise the measurements with the subjective perception? So there is an equalisation network, or called the weighting network, the low and high frequencies are moderately attenuated, so that the mid-range frequencies will be more prominent. This weighted network connected to the equipment being measured and measuring instruments, so the equipment will be the impact of mid-frequency noise network "amplification", in other words, the greatest impact on the sense of hearing the mid-frequency noise is given a higher weighting, this time the measured signal-to-noise ratio is called the weighted signal-to-noise ratio, which can be more truly reflecting the subjective sense of human hearing.
Depending on the weighting network used, they are called A sound level, B sound level and C sound level, and the units are recorded as dB(A), dB(B) and dB(C). A weighted sound level simulates the frequency characteristics of the human ear for low-intensity noises of less than 55dB, B weighted sound level simulates the frequency characteristics of medium-intensity noises of 55dB to 85dB, and C weighted sound level simulates the frequency characteristics of high-intensity noises. The main difference between the three is the attenuation of the low-frequency components of the noise, with A attenuating the most, B the second, and C the least. A-weighted sound level is the most widely used in the world for noise measurement because its characteristic curve is close to the auditory characteristics of the human ear, and many national norms related to noise are based on A-weighted level as an index.
