Study on strategy of multiple-duct active silencer system

摘要

Large ventilation systems used in subways, underground substations, and other underground facilities have ducts of several meters square, and the noise caused by these systems has generated a need for active noise control that targets higher mode components in addition to plane waves. To this end, a multiple-duct active-silencer system can be considered in which multiple active silencers are installed along a cellular duct system, but degradation in noise reduction has been an issue in this system. We therefore performed a study on duct structure in the multiple-duct active-silencer system by analyzing sound fields inside ducts using the finite element method and by performing experiments with prototype equipment. To achieve noise reduction of 15 dB, it was found that sound power of flowing sound from secondarily noise source among the multiple ducts must be suppressed by at least 18%. In this regard, an effective means of accomplishing this was found to be a duct extension on the downstream side where secondarily noise originates.