Introduction and Operation Method of Sound Level Meter
A sound level meter is equipped with three standard frequency weighting networks: A, B and C. The A‑weighting network simulates the human ear's response to a 40‑phon pure tone on the equal‑loudness contour. Its weighting characteristic is opposite to the 340‑phon equal‑loudness curve, providing significant attenuation for the mid and low frequency components of electrical signals. The B‑weighting network simulates human auditory response to a 70‑phon pure tone and offers moderate attenuation in the low‑frequency range. The C‑weighting network corresponds to the human ear's perception of a 100‑phon pure tone, delivering an approximately flat response across the entire audio frequency range.
The sound pressure level measured through frequency weighting networks is defined as sound level. Depending on the selected weighting mode, readings are classified as A-weighted sound level, B-weighted sound level and C-weighted sound level, with units marked as dB(A), dB(B) and dB(C).
Currently, the meter response of noise measurement instruments is divided into four types according to time characteristics:
Slow ResponseWith a time constant of 1000 ms, it is mainly used for steady noise measurement and outputs effective value readings.
Fast ResponseWith a time constant of 125 ms, it applies to fluctuating unsteady noise, traffic noise and similar sound sources. This mode closely matches the human ear's auditory reaction speed.
Impulse / Impulse HoldThe needle rise time is 35 ms, designed for long-duration impulse noise such as stamping and forging equipment. It captures the maximum effective value.
Peak HoldThe needle rise time is less than 20 ms, suitable for short-duration impulsive sounds including gunfire, artillery blasts and explosions. It records the peak value, namely the maximum instantaneous sound level.
