Principle of Noise Meter
The sound pressure level measured by the sound level meter through the frequency weighting network is called the sound level. According to the different weighting network used, it is called the A sound level, the B sound level and the C sound level, and the unit is recorded as dB(A). , dB(B), and dB(C).
For the sound level meter used for measuring noise, the response of the meter head can be divided into four types according to the sensitivity:
1. "Slow": the time constant of the meter head is 1000ms, which is generally used to measure steady-state noise, and the measured value is the effective value.
2. "Fast": The time constant of the meter head is 125ms, which is generally used to measure unstable noise and traffic noise with large fluctuations. Fast gear is close to the human ear's response to sound.
3. "Pulse or pulse hold": the rising time of the needle is 35ms, which is used to measure the pulse noise with a long duration, such as punches, hammers, etc. The measured value is the maximum effective value.
4. "Peak hold": the rise time of the needle is less than 20ms. Used to measure short-duration impulse sounds, such as guns, cannons and explosions, the measured value is the peak value. i.e. the maximum value.
The sound level meter can be connected to an external filter and recorder to perform spectrum analysis on noise. The domestic ND2 type precision sound level meter is equipped with an octave page filter, which is easy to carry to the scene and perform spectrum analysis. Sound level meters can be divided into precision sound level meters and ordinary sound level meters according to their accuracy. The measurement error of a precision sound level meter is about ±1dB, and that of an ordinary sound level meter is about ±3dB.
Sound level meters can be divided into two categories according to their use: one is used to measure steady-state noise, and the other is used to measure unsteady noise and impulse noise.
The integrating sound level meter is used to measure the equivalent sound level of unsteady noise over a period of time. A noise dosimeter is also an integrating sound level meter, mainly used to measure noise exposure. Impulse sound level meter is used to measure impulse noise, this kind of sound level meter accords with human ear's response to impulse sound and the average time of human ear's response to impulse sound.
