Acoustical characteristics of the sound absorption structure with densely arrayed capillary tube bundles

Based upon the perforated panel resonator with tube bundles, in order to broaden the sound absorption frequency bandwidth and avoid using the fiber porous material in high temperature and hygiene environment, a new type sound absorption structure with densely arrayed capillary tube bundles (DACTB) is presented in this paper. The acoustical impedance tube measurements show that the DACTB has a wider frequency range of sound absorption which is similar to that of traditional porous materials. The DACTB avoids the inherently excessive fluctuation of sound absorption for traditionally acoustical resonators. Its analytical models of acoustic impedance and sound absorption coefficients are established. Its sound absorption characteristics are studied and compared by both experimental and theoretical methods. The effects of its geometric parameters, such as the length and inner diameter of the capillary tube, on the sound absorption performance are predicted. The experiment and calculation results indicate that with the increase of the length of the capillary tube bundles, the sound absorption effect is increased, especially in low frequency range. Meanwhile with the change of the inner diameter of the capillary tube bundles, the results show that there is an optimum value of the inner diameter of the capillary tube bundles with respect to the sound absorption performance. The DACTB as a non-fiber broadband sound absorber provides some potential applications in high temperature noise reduction of inlet and exhaust ducts of aircraft engine nacelle and diesel engine as well as rocket engine.