Principle and introduction of the decibel meter - Noise meter - Sound level meter
A noise meter is the most basic instrument in noise measurement. Noise meters are generally composed of a condenser microphone, a preamplifier, an attenuator, an amplifier, a frequency weighting network, and an RMS indicator head. The working principle of the noise meter is: the microphone converts the sound into an electrical signal, and then the preamplifier converts the impedance to match the microphone with the attenuator. Amplifier will be added to the output signal weighting network, the signal frequency weighting (or external filter), and then by the attenuator and amplifier will be amplified to a certain amplitude of the signal, sent to the RMS detector (or outside the level recorder), in the indication of the meter head to give the numerical value of the noise level.
Standard weighting of noise meters
The frequency weighting network of noise meter has three standard weighting networks: A, B and C. A network simulates the response of the human ear to the 40-square pure tones in the equal-loudness curve, which is opposite to the equal-loudness curve of the 340-square curve, thus making the middle and low-frequency bands of the electrical signals to have a larger attenuation; B network simulates the response of the human ear to the 70-square pure tones, which makes the low-frequency bands of the electrical signals to have certain attenuation; C network simulates the response of the human ear to the 100-square pure tones. Network C simulates the response of the human ear to a 100-square tone and has a nearly flat response over the entire frequency range. The sound pressure level measured by a noise meter through a frequency weighting network is called the sound level, and depending on the weighting network used, it is referred to as the A level, the B level and the C level, with the units recorded as dB(A), dB(B) and dB(C).
