Noise Meter Principle and Noise Standard
A microphone is a device that converts a sound pressure signal into a voltage signal, also known as a microphone, and it is a sensor of a noise meter. Common microphones are crystal, electret, moving coil and condenser.
A moving coil microphone is composed of a vibrating diaphragm, a movable coil, a permanent magnet and a transformer. The vibrating diaphragm begins to vibrate after being subjected to sound wave pressure, and drives the movable coil installed with it to vibrate in the magnetic field to generate an induced current. The current varies according to the magnitude of the acoustic pressure on the vibrating diaphragm. The greater the sound pressure, the greater the current generated, and the smaller the sound pressure, the smaller the current generated.
The condenser microphone is mainly composed of a metal diaphragm and metal electrodes that are close together, which is essentially a flat plate capacitor. The metal diaphragm and the metal electrode constitute the two plates of the flat capacitor. When the diaphragm is subjected to sound pressure, the diaphragm deforms and the distance between the two plates changes, thus changing the capacitance. The voltage in the bit measurement circuit also changes, realizing the function of converting the sound pressure signal into a voltage signal. Condenser microphone is an ideal microphone in acoustic measurement. It has the advantages of large dynamic range, flat frequency response, high sensitivity and good stability in general measurement environment, so it is widely used. Since the output impedance of the condenser microphone is very high, it is necessary to perform impedance transformation through the preamplifier, and the preamplifier is installed inside the noise meter near the place where the condenser microphone is installed.
Noise standard:
A noise level of 30 to 40 decibels is a relatively quiet normal environment; more than 50 decibels will affect sleep and rest. Due to lack of rest, fatigue cannot be eliminated, and normal physiological functions will be affected to a certain extent; more than 70 decibels interfere with conversation, causing distraction, lack of concentration, affecting work efficiency, and even accidents; long-term work or living at noises above 90 decibels The environment can seriously affect hearing and lead to the occurrence of other diseases.
The basic standard of environmental noise is the basic basis for formulating environmental noise standards. Most countries refer to the base number recommended by ISO (such as 30 decibels for sleep), and formulate environmental noise standards according to different regions, different times of the day, correction values of indoor noise affected by outdoor noise, and national and local economic and technical conditions.
Indoor noise standards can be divided into residential and non-residential. Residential indoor noise standards are formulated according to the requirements of quiet life and the environmental noise standards of the area, with reference to the conditions of residential windows, and generally should not be lower than the environmental noise standards of the area by 20 decibels. The standard for residential buildings in China is 10 decibels lower than the ambient noise standard in the area, because there are many small factories close to residential buildings in Chinese cities. Non-residential indoor noise standards are stipulated according to the purpose of the room. General noise standards for various rooms of non-residential buildings.
