What is a noise meter and how it works:
A noise meter/sound level meter is the most basic instrument in noise measurement. The noise meter/sound level meter is generally composed of a condenser microphone, a preamplifier, an attenuator, an amplifier, a frequency weighting network, and an RMS indicator.
The working principle of the noise meter/sound level meter is: the microphone converts the sound into an electrical signal, and then the preamplifier transforms the impedance to match the microphone and 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 amplifier, and sends it to the RMS detector (or external power supply). flat recorder), the numerical value of the noise sound level is given on the indicator head. The frequency weighting network in the noise meter/sound level meter has three standard weighting networks, A, B, and C. The A network simulates the response of the human ear to the 40-square pure tone in the equal-loudness curve. 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 simulates the response of the human ear to a 70-square pure tone, which makes the low frequency band of the electrical signal attenuated to a certain extent. The C network simulates the human ear's response to a 100-square pure tone, with a nearly flat response over the entire audio frequency range.
The sound pressure level measured by the noise meter/sound level meter through the frequency weighting network is called sound level. According to the different weighting network used, it is called A sound level, B sound level and C sound level, and the unit is denoted as dB. (A), dB(B) and dB(C).
At present, the noise meter/sound level meter used for noise measurement can be divided into four types according to the sensitivity of the meter head: (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) "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 rise time of the needle is 35ms, which is used to measure pulse noise with a long duration, 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. Used to measure short-duration impulse sounds, such as guns, cannons and explosions, the measured value is the peak value. That is, the maximum value. The noise meter/sound level meter can be connected to an external filter and recorder for spectrum analysis of noise. The domestic ND2 precision noise meter/sound level meter is equipped with an octave page filter, which is easy to carry to the scene and for spectrum analysis.
Noise meter/sound level meter can be divided into precision noise meter/sound level meter and ordinary noise meter/sound level meter according to the accuracy. The measurement error of the precision noise meter/sound level meter is about ±1dB, and the ordinary noise meter/sound level meter is about ±3dB.
Noise meters/sound level meters can be divided into two categories according to their application: one is used to measure steady-state noise, and the other is used to measure unsteady noise and impulse noise. The integrating noise meter/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 noise meter/sound level meter, mainly used to measure noise exposure. Impulse noise meter/sound level meter is used to measure impulse noise. This TES noise meter/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.
