Frequency weighting for sound level measuring
The frequency weighting network in the sound level meter has three standard weighting networks: A, B, and C. It is a correction circuit designed to correct the auditory experience based on the response characteristics of the human ear to sound. It attenuates sounds of different frequencies to varying degrees according to equal loudness curves. The A-weighted network simulates the human ear's response to the 40-square pure tone in the equal loudness curve. Its curve shape is opposite to the 40-square equal loudness curve, which causes greater attenuation in the mid- and low-frequency bands of the electrical signal. The B-weighted network simulates the human ear's response to a 70-meter pure tone, which attenuates the low-frequency band of the electrical signal to a certain extent. The C-weighted network simulates the response of the human ear to 100 square meters of pure tone, and has an almost flat response in the entire audio frequency range.
The sound pressure level measured through the weighting network is no longer the sound pressure level of an objective physical quantity (also called linear sound pressure level), but the sound pressure level modified by the sense of hearing, which is called weighted sound level. The sound pressure level measured by the sound level meter through the frequency weighting network is called the sound level. The sound level reading obtained from the sound level meter must indicate the measurement conditions. For example, if an A-weighted network is used and the unit is dB, it should be recorded as dB (A). Depending on the weighting network used, they are called A sound level, B sound level and C sound level respectively, and the units are recorded as dB (A), dB (B) and dB (C). For example, if 70dB data is measured using C weighting, it should be recorded as 70dB (C) or C sound level 70dB. If 50dB data is measured using A weighting, it should be recorded as 50dB (A) or A sound level 50dB.
