Working principle and technical indicators of sound level meter
Sound level meter, also known as noise meter, is the most basic noise measurement instrument. It is an electronic instrument, but different from objective electronic instruments such as voltmeter. When converting sound signals into electrical signals, the time characteristics of the human ear's response speed to sound waves can be simulated; The frequency characteristics with different sensitivities to high and low frequencies, as well as the intensity characteristics that change the frequency characteristics at different loudness levels. Therefore, a sound level meter is a subjective electronic instrument.
Signal to Noise Ratio: Binary Signal to Noise Ratio, also known as SNR or SNR, refers to the ratio of useful signal power to useless noise power (the ratio between the maximum undistorted sound signal intensity produced by a sound source and the noise intensity emitted simultaneously, usually expressed in decibels (dB))
For example, we know that when listening to radio or recording music on a tape recorder, there are always various miscellaneous sounds in the speaker in addition to the broadcast and music sounds. Some of these noises are caused by interference from lightning, motors, electrical equipment, etc; Some are generated by the components and parts of the electrical equipment itself. All these noises are called noise. The smaller the noise, the clearer the broadcast and music sound. In order to measure the quality of electroacoustic equipment, the technical indicator of "signal-to-noise ratio" is commonly used. The so-called signal-to-noise ratio refers to the ratio of the useful signal power S to the noise power N, denoted as S/N.
Weighted: Weighted, also known as weighted or auditory compensation, has two meanings: one is the artificial correction added to the measured value considering the different conditions of the equipment during normal use and measurement, which is called weighting. Or it can be understood as: a correction coefficient added in the measurement to accurately reflect the measured object (which is also a standard set by the country to unify noise measurement). When measuring noise, due to the high sensitivity of the human ear to 1-5kHz and insensitivity to low-frequency components, when evaluating the noise level from an auditory perspective, it is necessary to weight each part of the audio spectrum. That is, when measuring noise, it needs to pass through a filter equivalent to the auditory frequency characteristics to reflect the human ear's keen sensitivity around 3000Hz and poor sensitivity at 60Hz. This is called weighting. Due to the frequency response of the human ear varying with the loudness of sound, different weighting curves are used for sounds of different loudness or pressure levels. At present, the weighted curve A is commonly used, and the measured value of this A-weighted curve is represented in dBA.
Frequency weighting (weighting network): In order to simulate the different sensitivities of human auditory perception at different frequencies, there is a network that can simulate the auditory characteristics of the human ear and correct electrical signals to approximate auditory perception. This network is called a weighting network. 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.
