抄録
A typical ceiling-mounted ventilator consists of a cylindrical fan unit and a rectangular box as an outer cover. When the box is appropriately closed by an orifice plate in front of the fan, the space enclosed by the box and plate acts as a sound resonator. In the present study, the performance and physical aspect of this resonator are investigated experimentally using a model of a rectangular chamber containing an internal cylinder placed in an infinite circular duct. The sound transmission loss of the chamber is measured while varying the chamber length and the inlet length. The experimental model verified the effect of an actual ventilator. Two resonances appear in the frequency range of interest. These resonance frequencies are determined using a relatively simple estimation. In addition, for modulating the chamber property, a thin circular plate or a thin cylindrical pipe, called a “separator,” is attached to the chamber. The performance of the separator, which modulates the resonance frequency, is examined. If the orifice plate and the separator are combined and arranged appropriately, they can promote sound attenuation in actual ceiling-mounted ventilators.
