Sound Level Meter (Noise Meter) Noise Measurement Principle
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 converts 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. 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 shape of 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 degree of attenuation. The C network simulates the response of the human ear to a 100-square pure tone, which has a nearly flat response over the entire frequency range of the sound. 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, the B sound level and the C sound level, and the units are recorded as dB(A), dB(B) and dB(C).
The sound level meter can be connected to external filters and recorders to do spectrum analysis of noise. The domestic ND2 type precision sound level meter is equipped with an octave page range filter, which is easy to carry to the site and make 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 the precision sound level meter is about 1dB, and that of the ordinary sound level meter is about 3dB. The sound level meter can be divided into two categories according to its use: one is used to measure steady state noise, and the other is used to measure unsteady state noise and impulse noise. Integral 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.
