Noise Meter Noise Reduction Methods and Principles of Application
A sound level meter, also known as a noise meter, is a *basic* instrument for noise measurement. A sound level meter generally consists of a condenser microphone, a preamplifier, an attenuator, an amplifier, a frequency weighting network, and an RMS indicator head.
The working principle of a 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. Amplifier will be added to the output signal weighting network, the signal frequency weighting (or external filter), and then by the attenuator and amplifier will be amplified to a certain amplitude of the signal, sent to the effective value of the detector (or outside the level recorder), in the indication of the meter head to give the numerical value of the noise sound level.
The frequency weighting network in the 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 tones in the equal-loudness curve, which is opposite to the equal-loudness curve of the 340-square curve, thus making the middle and low frequency bands of the electrical signals to have a larger attenuation. the 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 certain attenuation. the C network simulates the response of the human ear to the 100-square pure tones, which has a certain attenuation. Network C simulates the response of the human ear to a 100-square tone and has a nearly flat response over the entire frequency range. The sound pressure level measured by a sound level meter through a frequency weighting network is called the sound level, and depending on the weighting network used, it is known as the A sound level, B sound level and C sound level, with the units recorded as dB(A), dB(B) and dB(C).
At present, the measurement of noise with a sound level meter, the meter head response according to the sensitivity can be divided into four kinds: (1) "slow". (1) "Slow", head time constant of 1000ms, - generally used to measure steady state noise, the measured value for the effective value. (2) "Fast". The time constant of the meter head is 125ms, which is generally used for the measurement of large fluctuation of unsteady noise 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. Sound level meter can be connected to external filters and recorders, to do spectrum analysis of noise. Domestic ND2 type precision sound level meter is equipped with an octave page range filter, easy to carry to the scene and for spectrum analysis.
Sound level meter can be divided into precision sound level meter and common sound level meter according to the accuracy. The measurement error of precision sound level meter is about 1dB, ordinary sound level meter is about 3dB. sound level meter can be divided into two categories according to the use: one category is used to measure the steady state noise, and one category is used to measure the unsteady state noise and impulse noise. An 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 and is primarily used to measure noise exposure. Impulse Sound Level Meters are used to measure impulse noise, which corresponds to the response of the human ear to impulse sound and the averaging time of the human ear's response to impulse sound.
