The structure and principle of sound level meter
Sound level meters are generally composed of microphones, amplifiers, attenuators, weighting networks, detectors and indicators
①Microphone: A transducer element that converts an acoustic signal (sound pressure) into an electrical signal (voltage). There are crystal microphones, electric microphones and electret microphones. Condenser microphones have the advantages of wide dynamic range, flat frequency response, small sensitivity change, and long-term stability, and are mostly used in precision sound level meters and standard sound level meters.
②Amplifier: Amplify weaker electrical signals. The amplifier used in the sound level meter requires high input impedance and low output impedance, reasonable dynamic range, small linear distortion and a frequency range that meets the needs. Includes input amplifier and output amplifier.
③Attenuator: The range of the sound level meter is generally 25-130dB. The detector and the analog indicator do not have such a wide range. Usually, the attenuator is used to attenuate the strong signal to avoid overloading the amplifier. Attenuators are divided into input attenuators and output attenuators. In order to improve the signal-to-noise ratio, the input attenuator is located before the input amplifier, and the output attenuator is connected between the input amplifier and the output amplifier. In order to improve the signal-to-noise ratio, the output attenuator should be adjusted to the maximum attenuation level during measurement. On the premise that the input amplifier is not overloaded, the input attenuator should be adjusted to the minimum attenuation level, so that the input signal and the electrical noise of the input amplifier are different. as large a difference as possible.
④Weighting network: According to the provisions of IEC, several curves close to the human ear's response to sound frequency are selected, and A. b. c. D Four standard weighted networks. The frequency response curve of the A-weighted network is approximately equivalent to the inverted curve of the 40phon equal-response curve, so that the middle and low frequency bands of the electrical signal are attenuated to a certain extent, and the high frequency band is also attenuated to a certain extent. The B-weighting network is approximately equivalent to the inverted curve of the 70phon equal-loudness curve, so that the electrical signal is mainly attenuated in the low frequency band. The C-weighted network is equivalent to the inverted curve of the 100phon equal-loudness curve, and has a nearly flat response in the entire audio frequency range, which is approximately equivalent to the human ear's response to high-frequency sound. by A. b. c. The reading measured by the D-weighting network is called the sound level, and the sound level is the sound pressure level after frequency weighting, which should be distinguished from the sound pressure level.
The A-weighted frequency response is adapted to the sensitivity of the human ear to a wide range of frequency sounds, so z is commonly used in practical measurements. D-weighted networks are often used to measure aviation noise.
