Noise Pollution Caused by Low Frequency Sound in A Channel

Noise is one of the most important environmental problems in industrialized societies and developing countries. According to world health organization report، in European Union countries about 40% of the populations are exposed to road traffic noise with an equivalent sound pressure level of 55 decibels during a day. The study was conducted by a signal processing software (Matlab) which is one of the most powerful mathematical software for processing and generating signals. First the signal was produced at the frequencies of 50-500 Hz and 1000-6000 Hz، then it propagated along a duct with dimensions of 20 × 20 × 150 cm. These signals were sampled by transferring them with order through the channels with sampling rate of 8000 Hz and sampling time of 10 seconds. Reduction of amplitude about 0. 05 at 500 and 0. 15 at 250 frequencies for low frequency noise was observed. At frequencies of 1000، 4000، and 6000 Hz، there was a reduction of 0. 02، 0. 01، and 0. 004 of amplitude، respectively. The figures showed that as the frequency increased the amplitude decreased، while the amplitude of low frequency noise increased. From the figures and the obtained information it can be noted that due to the high power of low frequency noise at ventilation duct، specific effects and unavoidable disorders were caused. However، strengthening low frequency noise in channels and ventilation ducts can be confirmed. Low frequencies noise in the distribution channel، with increase in the length of the channel can reach to its maximum amplitude.