The meaning of weighting of noise meters (sound level meters)
Signal Noise Ratio, referred to as signal-to-noise ratio or signal-to-noise ratio
It refers to the ratio of useful signal power to useless noise power. Usually measured in shells. Because power is a function of current and voltage, the signal-to-noise ratio can also be calculated using voltage values, that is, the ratio of signal level to noise level, but the calculation formula is slightly different. Calculate the signal-to-noise ratio based on the power ratio: S/N=10 log Calculate the signal-to-noise ratio based on the voltage: S/N=10 log Since the signal-to-noise ratio has a logarithmic relationship with power or voltage, to improve the signal-to-noise ratio, it must be larger Significantly increase the ratio between the output value and the noise value. For example, when the signal-to-noise ratio is 100dB, the output voltage is 10,000 times the noise voltage. In terms of electronic circuits, this is not an easy task.
Behind the specification table data in the product manual, there is often the word A, which means A-weight, which means A-weighting. Weighting means that a certain value has been modified according to certain rules to weigh the severity. Because the human ear It is particularly sensitive to mid-frequency, so if the signal-to-noise ratio of an amplifier in the mid-frequency band is large enough, even if the signal noise is slightly lower than the low-frequency and high-frequency bands, it will not be easily detected by the human ear. It can be seen that if the weighting method is used to measure the signal-to-noise ratio, the value will definitely be higher than that without the weighting method. In terms of A weighting, its value is higher than that without weighting.
In addition, in order to simulate the different sensitivities of human hearing at different frequencies, the sound level meter is equipped with a network that can simulate the hearing characteristics of the human ear and modify the electrical signal to an approximate value of the sense of hearing. This network is called weighted network. The sound pressure level measured through the weighting network is no longer the sound pressure level of an objective physical quantity (called linear sound pressure level), but the sound pressure level modified by the sense of hearing, called weighted sound level or noise level.
There are generally three types of weighted networks: A, B, and C. The A-weighted sound level simulates the frequency characteristics of the human ear to low-intensity noise below 55dB, the B-weighted sound level simulates the frequency characteristics of medium-intensity noise from 55dB to 85dB, and the C-weighted sound level simulates the frequency of high-intensity noise. characteristic. The main difference between the three is the degree of attenuation of the low-frequency component of the noise. A has the most attenuation, followed by B, and C the least. A-weighted sound level is currently the most widely used in noise measurement in the world because its characteristic curve is close to the physical properties of the human ear. B and C are gradually no longer used.
