Principle of operation of sound level meter and its technical specifications
Sound level meter, also called noise meter is the most basic noise measurement instrument, it is an electronic instrument, but different from the voltmeter and other objective electronic instruments. In the acoustic signal into an electrical signal, you can simulate the human ear to the sound wave reaction speed of the time characteristics; on the high and low frequencies have different sensitivity to the frequency characteristics as well as different loudness when changing the frequency characteristics of the intensity characteristics. Therefore, the sound level meter is a subjective electronic instrument.
Signal to Noise Ratio: The signal to noise ratio (Signal NoiseRatio), referred to as the signal to noise ratio or signal to noise ratio, refers to the ratio of the useful signal power to the unwanted noise power (the sound source produces the maximum undistorted sound signal strength and the noise intensity of the noise intensity at the same time between the ratio, usually in terms of the "SNR" or "S / N" said, generally in decibels (dB) as a unit, the higher the better the signal-to-noise ratio).
Example: We know that when a radio listens to a broadcast or a tape recorder plays music, the loudspeaker, in addition to the sound of the broadcast and the sound of the music, always contains a variety of noises. These noises are lightning, motor, electrical equipment and other interference; some are electric body equipment itself, the components, devices. All these noises we call noise. The smaller the noise, the clearer the radio and music will sound. In order to measure the quality of electro-acoustic equipment, commonly used "signal-to-noise ratio" as a technical indicator. The so-called signal-to-noise ratio is the ratio between the useful signal power S and the noise power N, which is written as S/N.
Weighted (weighted): Weighted (Weighted), also known as weighted or listening compensation, has two meanings: one is to take into account the equipment in normal use and measurement of different conditions, the measured value of the artificial correction, known as weighted. Or it can be understood as: a correction factor attached to the measurement to correctly reflect the measured object (which is also a standard set by the state in order to unify the noise measurement). Such as in the measurement of noise, due to the human ear on the 1 ~ 5kHz sensitivity * high, the low-frequency component is not sensitive, from the auditory evaluation of the noise size, it is necessary to evaluate the various parts of the audio spectrum weighting, that is, in the measurement of the noise needs to be made to pass through a filter with the auditory frequency characteristics of the equivalent to reflect the human ear in the vicinity of the 3000Hz sharp sensitivity and 60Hz when the poorer sensitivity, which is weighting This is called weighting. Since the frequency response of the human ear varies with the loudness of the sound, different weighting curves are used for different loudness or sound pressure levels. Currently, the weighting curve A is commonly used, and dBA is used to express the measured value of this A-weighting.
