There are three standard weighting networks in sound level meters: A, B, and C. The A network simulates the response of the human ear to a 40 square pure tone in the equivalent response curve. Its curve shape is opposite to the 340 square equivalent response curve, resulting in significant attenuation in the middle and low frequency bands of the electrical signal. The B-network simulates the response of the human ear to 70 square pure tones, which attenuates the low-frequency range of electrical signals to a certain extent. The C network simulates the response of the human ear to 100 square pure tones, with a nearly flat response throughout the entire audio frequency range. The sound pressure level measured by the sound level meter through a frequency weighting network is called the sound level. Depending on the weighting network used, it is called the A sound level, B sound level, and C sound level, with units recorded as dB (A), dB (B), and dB (C).
(1) Slow. The time constant of the meter head 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 head is 125ms, which is generally used to measure unstable noise and transportation noise with significant fluctuations. The fast gear approaches the human ear's response to sound.
(3) Pulse or pulse hold. The rise time of the watch needle is 35ms, used to measure pulse noise with a longer duration, such as punching machines, press hammers, etc. The measured value is the maximum effective value.
(4) Peak Hold. The rise time of the watch needle is less than 20ms. It is used to measure pulse sounds with a short duration, such as guns, artillery, and explosive sounds. The measured value is the peak value, which is the maximum value.
The sound level meter can be connected to an external filter and recorder for spectral analysis of noise. The domestically produced ND2 precision sound level meter is equipped with an octave bandpass filter, which is easy to carry to the site and perform spectral analysis. Sound level meters can be divided into precision sound level meters and ordinary sound level meters based on accuracy. The measurement error of a precision sound level meter is about 1dB, while that of a regular sound level meter is about 3dB. Sound level meters can be divided into two categories according to their purpose: one is used to measure steady-state noise, and the other is used to measure unstable noise and pulse noise. An integral sound level meter is used to measure the equivalent sound level of unstable noise over a period of time. A noise dosimeter is also an integral sound level meter, mainly used to measure noise exposure. Pulse sound level meters are used to measure pulse noise, which correspond to the response of the human ear to pulse sound and the average time of the human ear's response to pulse sound.
