The A network simulates the human ear's response to the 40-square pure tone in the equal loudness curve. Its curve shape is opposite to the 340-square equal loudness curve, which causes greater attenuation in the mid- and low-frequency bands of the electrical signal. The B network simulates the human ear's response to a 70-meter pure tone, which attenuates the low-frequency band of the electrical signal to a certain extent.
The C network simulates the response of the human ear to 100 square meters of pure tone, and has an almost flat response in the entire audio frequency range. The sound pressure level measured by the sound level meter through the frequency weighting network is called sound level. Depending on the weighting network used, it is called A sound level, B sound level and C sound level respectively. The unit is recorded as dB(A) , dB(B) and dB(C).
(1) "Slow". The time constant of the meter is 1000 ms, which is generally used to measure steady-state noise, and the measured value is the effective value.
(2) "Quick". The time constant of the meter is 125ms, which is generally used to measure unstable noise and transportation noise with large fluctuations. Fast gears are close to how the human ear responds to sound.
(3) "Pulse or pulse hold". The rising time of the needle is 35ms, which is used to measure long-duration pulse noise, such as punches, hammers, etc. The measured value is the maximum effective value.
(4) "Peak hold". The rising time of the needle is less than 20ms. It is used to measure short-duration pulse sounds, such as guns, cannons and explosions. The measured value is the peak value, which is the maximum value. Sound level meters can be connected to external filters and recorders to conduct spectrum analysis of noise.
The accuracies of sound level meters are: Level I accuracy ±0.7dB, Level II accuracy ±1dB, Level III accuracy ±1.5dB, and ordinary sound level meters are ±2dB.
Sound level meters can be divided into two categories according to their uses: one is used to measure steady-state noise, and the other is used to measure unsteady-state noise and impulse noise.
