AN EXPERIMENTAL STUDY OF THE HERSCHEL-QUINCLE (HQ) TUBE NOISE ATTENUATION PERFORMANCE
The work presented in this paper summarize both analytical and experimental investigations of the Herschel-Quincke (HQ) concept for reducing known radiated inlet noise using signal generating system. The analytical part of this work involves one-dimensional plane wave propagate in a cylindrical duct. In this paper adaptive HQ tube is used to reduce tonal noise propagating as plane waves in closed end duct. The effect of HQ tube length on the noise reduction, induced by a loudspeaker at various frequencies, is investigated experimentally in an acoustically cylindrical duct with and without HQ. Five HQ tubes with different lengths are investigated. The distance between the HQ tube ends is kept constant (l=20 cm), ( = 1.5, 2.5, 3, 3.5, and 4). Two Microphones system was used to measure the net acoustic power transmission in the duct. One microphone is located just before the HQ tube in the duct, and the other is at the closed end of the duct where it is always anti-node pressure. Data acquisition, monitoring and analysis are done using National Instrument DAQ card and LabVIEW software. A LabVIEW vi code is developed to interface and process the two microphones system signals. Results showed that the length of the HQ tube is very important for a passive control of the noise reduction. While long HQ tube was effective in noise reduction in low frequencies, short HQ tube was more effective for high frequencies.