The method and principle application of noise meter to reduce noise
Sound level meter, also known as (noise meter) is the most basic instrument in noise measurement. A sound level meter is generally composed of a condenser microphone, a preamplifier, an attenuator, an amplifier, a frequency weighting network, and an effective value indicating meter.
The working principle of the sound level meter is: the microphone converts the sound into an electrical signal, and then the preamplifier transforms the impedance to match the microphone with the attenuator. The amplifier adds the output signal to the weighting network, performs frequency weighting on the signal (or an external filter), and then amplifies the signal to a certain amplitude through the attenuator and the amplifier, and sends it to the RMS detector (or an external circuit filter). Level recorder), the value of the noise level is given on the indicator head.
The frequency weighting network in the sound level meter has three standard weighting networks: A, B, and C. The A network is to simulate the human ear's response to the 40-square pure tone in the equal-loudness curve, and its curve shape is opposite to the 340-square equal-loudness curve, so that the middle and low frequency bands of the electrical signal have greater attenuation. The B network is to simulate the human ear's response to the 70-square pure tone, and it attenuates the low-frequency band of the electrical signal to a certain extent. The C network simulates the response of the human ear to a 100-square pure tone, and has a nearly flat response throughout the entire audio frequency range. The sound pressure level measured by the sound level meter through the frequency weighting network is called the sound level. According to the weighting network used, it is called A sound level, B sound level and C sound level, and the unit is recorded as dB(A) , dB(B) and dB(C).
At present, the sound level meter used to measure noise can be divided into four types according to the sensitivity of the meter head response:
(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 an 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. The 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 punch press, hammer, etc. The measured value is the maximum effective value.
(4) "Peak hold". The rise time of the watch hand is less than 20ms. It is used to measure the pulse sound with a short duration, such as guns, cannons and explosions. The measured value is the peak value. That is, the maximum value. The sound level meter can be connected with an external filter and recorder for spectrum analysis of the noise. The domestic ND2 precision sound level meter is equipped with an octave page filter, which is easy to carry to the scene and do 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 usage: one is used to measure steady-state noise, and the other is used to measure unsteady-state noise and impulse noise. Integrating sound level meters are used to measure the equivalent sound level of unsteady noise over a period of time. 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 sound level meter conforms to the human ear's response to impulse sound and the average time of human ear's response to impulse sound.
Factors Influencing the Selection of Noise Meter
The noise meter is mainly used to measure noise, and the classification of noise measurement mainly includes the following types:
1. From the measurement object, it can be divided into the characteristic measurement of environmental noise (sound field) and the measurement of sound source characteristics.
2. From the time characteristics of the sound source or sound field, it can be divided into steady-state noise measurement and unsteady-state noise measurement. Non-stationary noise can be divided into periodic noise, irregular noise and pulse sound.
3. From the frequency characteristics of the sound source or sound field, it can be divided into broadband noise, narrowband noise and noise containing prominent pure tone components.
4. From the accuracy of measurement requirements, it can be divided into precision measurement, engineering measurement and noise census.
