Abstract: Based on the principle of resonance to improve the sound intensity of loudspeaker, the effect of the sound characteristics of loudspeaker with different size of varying and constant cross-section tubes was studied by experiments. The results showed that the varying cross-section tubes are good radiators and the constant cross-section tubes of 1/4 wave length are good resonators. Air flow with sound periodically pass through varying cross-section tubes generating 137.2dB high intensity sound at 1m distance from the outlet of the tube, whereas 120dB for constant cross-section.