Noise measurement is the monitoring activity of the sounds and their sources that disturb people's learning, work, and living. This includes: noise monitoring in various functional zones of the city, traffic noise monitoring, regional environmental noise monitoring, and noise source monitoring, etc. The results of noise monitoring are generally expressed in A-weighted sound level, with the main instruments being sound level meters and spectrometers. The results of noise monitoring are used to analyze the current situation and changing trends of noise pollution, and also provide basic data for the planning and management of noise pollution and comprehensive treatment.
Methods of Noise Measurement:
Before measurement, check if the sound level meter's battery voltage meets the requirements and calibrate the sound level meter using a piston sound generator.
(2) Avoid wind, rain, and snow interference during noise measurement. When the wind speed exceeds grade 3, a windscreen should be added to the microphone; if the wind speed reaches grade 5 or above, stop the measurement.
(3) During measurements, the microphone should be as close as possible to the mechanical radiating surface to ensure a sufficient direct sound level from the noise source, avoiding interference from other noise sources. When using a handheld instrument, it should be kept as far from the body as possible. The microphone should be elevated off the ground.
Noise measurement as a test signal is essential for achieving broad-spectrum and dynamic measurements of the system's capability to utilize noise as a test signal. Generally, Gaussian white noise is used as the test signal, with a probability density function that is Gaussian (following a normal distribution) and a power density spectrum that is flat (over a bandwidth much wider than the one under study). For instance, in a multi-carrier multiplexing system, noise loading tests are conducted to estimate the system's internal parasitic background noise caused by intermodulation distortion and the activity of other channels. By adding white noise to the system, the actual activity in all channels is simulated, and a band-stop filter is used to keep the channel under test idle. Then, at the receiver end, a band-pass filter is employed to measure the idle channel's background noise, simulating the system's actual operating condition.
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