Study on acoustic characteristics of straight duct with some holes

Abstract

An air conditioning equipment is usually set in a rail vehicle in order to keep comfort. However the noise is offensive to the ear especially when the rail vehicle is in a stop. Then the noise reduction is very important from the point of view of keeping the car room comfortable and is one of the distinguished techniques. This paper describes acoustic characteristics of the duct with some holes. The acoustic experiments were carried out in various parameters such as the absorbing ability and the hole's area by use of the straight duct. As a result, it was clarified that the noise reduction effect of the absorbing treatment measured at the inside of the duct with holes was different from that measured at outside of the same duct. Moreover the effect of hole's area on the noise spectra was a little in spite of the presence of the absorbing treatment.