Abstract
The present study addresses experimental results to investigate the effect of the Herschel-Quincke (HQ) tube length on the reduction of noise. In this paper the detailed experiment is carried out in an acoustically cylindrical duct with and without HQ induced by a loudspeaker at various frequencies. Microphone system has been used to measure the net acoustic power transmission in the duct downstream with HQ tube and compared in the duct without the HQ tube. The acoustic wave signal is traveling in the duct as a plane wave; this wave is generated by a signal generating system with a known sinusoidal wave (sine wave). The microphone is located just after the HQ tube in the duct. In this paper two types of HQ tube have been studied, short HQ tube and long HQ tube. Labview software has been applied for data acquisition, monitoring and analysis. The analysis is done on the basis of time, history and power spectrum.This study makes an exhaustive understanding of power spectrum of two acoustic channels in the duct with and without HQ tube. The results show that there is a great potential for HQ tube system to attenuate the noise over cylindrical duct section. Results showed that, the effective reduction of noise was in the low frequencies range when long HQ tube is used, compared with short HQ tube, the reduction of noise was in high range of frequencies. That means the length of the HQ tube is very important for a passive control of the noise reduction in an industrial and turbofan engines applications.