Sound level meters used in the automotive industry
(1) Microphone
It is a device that converts sound pressure signals into voltage signals, also known as a microphone or sensor. Common types of microphones include crystal, electret, moving coil, and capacitive.
A dynamic coil sensor consists of a vibrating diaphragm, a movable coil, a magnet, and a transformer. After being subjected to acoustic pressure, the vibrating diaphragm begins to vibrate and drives the movable coil installed with it to vibrate in the magnetic field, generating induced current. The current varies according to the magnitude of the acoustic pressure acting on the vibrating diaphragm. The higher the sound pressure, the greater the generated current; The lower the sound pressure, the smaller the generated current.
(2) Amplifier and attenuator
Many popular domestic and imported amplifiers currently use two-stage amplifiers in amplification circuits, namely input amplifiers and output amplifiers, which amplify weak electrical signals. The input attenuator and output attenuator are used to change the attenuation of the input signal and the attenuation of the output signal, so that the pointer of the meter head points to the appropriate position, and the attenuation of each gear is 10 decibels. The adjustment range of the attenuator used in the input amplifier is for measuring the bottom end (such as 0-70 decibels), and the adjustment range of the attenuator used in the output amplifier is for measuring (70-120 decibels). The dials of the input and output attenuators are often made in different colors, and currently black and transparent are often paired together. Due to the fact that many sound level meters have a high and low limit of 70 decibels, it is important to prevent exceeding the limit during rotation to avoid damaging the device.
(3) Weighted network
In order to simulate the sensitivity of human auditory perception at different frequencies, there is a network called a weighted network that can simulate the auditory characteristics of the human ear and modify electrical signals to approximate auditory perception. The sound pressure level measured through a weighted network is no longer an objective physical quantity of sound pressure level (called linear sound pressure level), but a sound pressure level corrected for auditory perception, called weighted sound level or noise level.
