What is a noise meter and how it works
A noise meter/sound level meter is a *basic* instrument for noise measurement. Noise meters are generally composed of a condenser microphone, a preamplifier, an attenuator, an amplifier, a frequency weighting network, and an RMS indicator head.
The operating principle of a noise meter/sound level meter is that the microphone converts the sound into an electrical signal, and then the preamplifier converts the impedance to match the microphone to the attenuator. The amplifier will add the output signal to the counting network, the signal frequency counting (or external filter), and then by the attenuator and amplifier to amplify the signal to a certain amplitude, sent to the RMS detector (or external level recorder), in the indication of the meter head to give the value of the noise sound level. The frequency weighting network in the noise meter/sound level meter has three standard weighting networks, A, B and C. A network simulates the response of the human ear to the 40-square pure tones in the equal-loudness curve, which is opposite to the 340-square equal-loudness curve, thus making the middle and low frequency bands of the electrical signals to have a larger attenuation.B network simulates the response of the human ear to the 70-square pure tones, which makes the low-frequency bands of the electrical signals to have a certain attenuation.C network simulates the response of the human ear to the 100-square pure tones in the equal-loudness curve. simulates the response of the human ear to a 100-square pure tone, which has a nearly flat response over the entire range of sound frequencies.
The sound pressure level measured by a noise meter/sound level meter through a frequency weighting network is called the sound level, and depending on the weighting network used, it is referred to as the A sound level, the B sound level, and the C sound level, with the units noted as dB(A), dB(B), and dB(C).
At present, for noise meters/sound level meters used for measuring noise, the meter head response can be classified into four types according to sensitivity: (1) "Slow". (1) "Slow", with a head time constant of 1000 ms, is generally used to measure steady state noise, and the measured value is the RMS value. (2) "Fast". The time constant of the meter head is 125 ms, and it is generally used for the measurement of unsteady noise with large fluctuation and transport noise. The fast gear is close to the human ear's response to sound. (3) "Pulse or pulse hold". The rise time of the meter needle is 35ms, used for measuring impulse noise with long duration, such as punch, press hammer, etc. The measured value is the *large RMS value. (4) "Peak hold". The rise time of the meter needle is less than 20ms. It is used to measure the impulse sound with short duration, such as gun, cannon and explosion sound, and the measured value is the peak value. The measured value is the peak value, i.e. the *maximum* value. The noise meter/sound level meter can be connected to external filters and recorders to do spectrum analysis of noise. Domestic ND2 type precision noise meter / sound level meter is equipped with an octave page range filter, easy to carry to the scene and make spectrum analysis.
Noise meters/sound level meters can be divided into precision noise meters/sound level meters and ordinary noise meters/sound level meters according to their accuracy. The measurement error of precision noise meters/sound level meters is about 1dB, and that of ordinary noise meters/sound level meters is about 3dB.
Noise meters/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 state noise and impulse noise. An 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 and is primarily used to measure noise exposure. Impulse noise meter/sound level meter is used to measure impulse noise, this kind of TES noise meter/sound level meter conforms to the response of the human ear to impulse sound and the averaging time of the human ear's response to impulse sound.
