Classification and Usage Instructions of Sound Level Meters
According to the sensitivity of the whole sound level meter, there are two methods for classifying sound level meters: one is ordinary sound level meters, which do not require high requirements for the microphone. The dynamic range and frequency response flat range are relatively narrow, and generally do not configure bandpass filters for use in conjunction; Another type is precision sound level meters, whose microphones require wide frequency response, high sensitivity, good long-term stability, and can be used in conjunction with various bandpass filters. The amplifier output can be directly connected to level recorders and recorders to display or store noise signals. If the microphone of a precision sound level meter is removed and replaced with an input converter and connected to an accelerometer, it becomes a vibration meter that can be used for vibration measurement.
In recent years, some people have classified sound levels into four categories, namely 0, 1, 2, and 3. Their accuracies are ± 0.4 decibels, ± 0.7 decibels, ± 1.0 decibels, and ± 1.5 decibels, respectively.
A sound level meter is a fundamental instrument in noise measurement. A sound level meter generally consists of a condenser microphone, preamplifier, attenuator, amplifier, frequency weighting network, and effective value indicator head. The working principle of a sound level meter is that the sound is converted into an electrical signal by a microphone, and then the impedance is transformed by a preamplifier to match the microphone with an 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 an attenuator and amplifier, and sends it to the effective value detector (or an external level recorder). The noise level value is displayed on the indicator head.
There are three standard weighting networks for frequency in sound level meters: A, B, and C. The A network simulates the response of the human ear to a 40 square pure tone in an acoustic curve, and its curve shape is opposite to the 340 square acoustic curve, resulting in significant attenuation in the middle and low frequency bands of the electrical signal. B network simulates the response of the human ear to 70 square pure tones, which causes a certain attenuation in the low frequency range of electrical signals. The C network simulates the response of the human ear to 100 square tones, with a nearly flat response across the entire audio frequency range. The sound pressure level measured by a sound level meter through a frequency weighting network is called sound level. Depending on the weighting network used, it is referred to as A sound level, B sound level, and C sound level, with units denoted as dB (A), dB (B), and dB (C).
