According to the accuracy of the sound level meter measuring 1000Hz pure tone under standard conditions, the international sound level meter was divided into two categories in the 1960s, one was called precision sound level meter, and the other was called ordinary sound level meter. Our country also adopts this method.

1. The moving coil microphone is composed of a vibrating diaphragm, a moving coil, a magnet and a transformer, etc.

2. The condenser microphone is mainly composed of a metal diaphragm and metal electrodes that are close together, which is essentially a flat plate capacitor.

Generally, a two-stage amplifier is used, that is, an input amplifier and an output amplifier, and its function is to amplify weak electrical signals.

The adjustment range of the attenuator used by the input amplifier is to measure the low end, and the adjustment range of the attenuator used by the output amplifier is to measure the high end. The high and low ends of many sound level meters are bounded by 70dB.

(2) The microphone should be kept dry when not in use;

(3) The microphone diaphragm should be kept clean and must not be touched by hand;

⑷ When the instrument is not used for a long time, it should be powered on for 2 hours a month, and it should be powered on for 2 hours a week during the mildew rain season;

(5) The battery should be taken out in time after the instrument is used;

Since the 1970s, some countries have introduced a four-category method, which is divided into Type 0, Type 1, Type 2 and Type 3. Their accuracies are ±0.4dB, ±0.7dB, ±1.0dB, and ±1.5dB, respectively. According to the different power sources used by the sound level meter, it can also be divided into AC type and DC type sound level meter with dry batteries, and the latter can also be portable. Portable has the advantages of small size, light weight and convenient on-site use.