What are the components of a sound level meter.
A microphone is a device that converts sound pressure signals into voltage signals, also known as a sensor. Common types of microphones include crystal type, electret type, dynamic coil type, and capacitive type. A dynamic coil sensor consists of a vibrating diaphragm, a movable coil, a permanent magnet, and a transformer. After being subjected to sound wave pressure, the vibrating diaphragm begins to vibrate and drives the movable coil installed together with it to vibrate in the magnetic field, generating 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 generated current; The lower the sound pressure, the smaller the generated current
A capacitive sensor mainly consists of a metal film and a metal electrode that is very close to it, essentially a flat capacitor. The metal film and metal electrode form the two plates of a flat capacitor. When the diaphragm is subjected to sound pressure, it undergoes deformation, causing a change in the distance between the two plates and a change in capacitance, resulting in an alternating voltage. Its waveform is proportional to the sound pressure level within the linear range of the microphone, achieving the function of transforming the sound pressure signal into an electrical pressure signal.
Capacitive microphones are ideal microphones in acoustic measurements, with advantages such as large dynamic range, flat frequency response, high sensitivity, and good stability in general measurement environments, making them widely used. Due to the high output impedance of capacitive sensors, impedance transformation needs to be carried out through a preamplifier, which is installed inside the sound level meter near the location where the capacitive sensor is installed.
Many popular domestic and imported amplifiers and attenuators currently use two-stage amplifiers in amplification circuits, namely input amplifiers and output amplifiers, whose function is to amplify weak electrical signals. The input attenuator and output attenuator are used to change the attenuation of the input signal and the output signal, so that the pointer of the meter is in the appropriate position, and the attenuation of each gear is 10 decibels. The adjustment range of the attenuator used in the input amplifier is the measurement bottom (such as 0-70 decibels), and the adjustment range of the attenuator used in the output amplifier is the measurement high end (70-120 decibels). The dials of the input and output attenuators are often made in different colors, and currently black and transparent are commonly paired. Due to the fact that many sound level meters have a high and low limit of 70 decibels, it is necessary to prevent exceeding the limit during rotation to avoid damaging the device.
In order to simulate the different sensitivities of human auditory perception at different frequencies, the weighted network includes a network that can simulate the auditory characteristics of the human ear and correct electrical signals to be similar to auditory perception. This network is called a weighted network. The sound pressure level measured through a weighted network is no longer an objective physical quantity sound pressure level (called linear sound pressure level), but a sound pressure level corrected by auditory perception, called weighted sound level or noise level.
