![]() The metal diaphragm and the metal electrodes constitute the two plates of the flat capacitor. ![]() The greater the pressure, the greater the current generated the lower the sound pressure, the smaller the current generated.Ĭapacitive sensors are mainly composed of metal diaphragms and metal electrodes that are close to each other, which are essentially one flat capacitor. The current varies according to the magnitude of the acoustic pressure on the vibrating diaphragm. The vibrating diaphragm starts 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 induced current. The moving coil sensor is composed of a vibrating diaphragm, a movable coil, a magnet and a transformer. ![]() Common microphones include crystal, electret, moving coil, and condenser. It is a device that converts a sound pressure signal into a voltage signal, also known as a microphone, a sensor. The sound level meter consists of a microphone, an amplifier, an attenuator, a weighting network, a detector, an indicator head and a power supply. This weighting network is connected between the equipment under test and the measuring instrument, so the influence of the IF noise of the equipment will be "amplified" by the network, in other words, the IF noise that has the greatest impact on the sense of hearing is given a higher weight, the measured signal-to-noise ratio at this time is called the weighted signal-to-noise ratio, which can more truly reflect people's subjective sense of hearing. How to integrate the measured value with the subjective sense of hearing? So there is an equalization network, or a weighting network, which moderately attenuates both low and high frequencies, so that the middle frequency is more prominent. Therefore, the unweighted signal-to-noise ratio may not be as good as the human ear's subjective perception of the noise level. Since people have different perceptions of noise in each frequency band, they are sensitive to the intermediate frequency Z of about 3 kHz, but less to low frequency and high frequency. ![]() The sound pressure level measured by the weighting network is no longer the objective physical sound pressure level (called linear sound pressure level), but the sound pressure level corrected by the sense of hearing, which is called weighted sound level or noise level. In order to simulate the different sensitivities of human hearing at different frequencies (20Hz-20KHz), there is a network in the sound level meter that can simulate the auditory characteristics of the human ear and correct the electrical signal to a similar value to the sense of hearing. Level recorder), the value of the noise sound level is given on the indicator head. The amplifier adds the output signal to the weighting network, performs frequency weighting on the signal (or external filter), and then amplifies the signal to a certain amplitude through the attenuator and amplifier, and sends it to the rms detector (or external press). The sound is converted into electrical signals by the microphone, and then the impedance is transformed by the preamplifier to match the microphone and the attenuator. A sound level meter is a subjective electronic instrument. When converting an acoustic signal into an electrical signal, it can simulate the time characteristic of the human ear's response speed to the sound wave the frequency characteristic with different sensitivity to high and low frequencies and the intensity characteristic of changing the frequency characteristic at different loudness. But it is different from objective electronic instruments such as voltmeters. A sound level meter is a basic noise measuring instrument, which is an electronic instrument.
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