Abstract: This study addresses a persistent anomalous peak in the low-frequency sound absorption coefficient measurements obtained from a domestically manufactured impedance tube, aiming to improve measurement accuracy through structural optimization. First, modal testing of the tube was conducted, which ruled out measurement errors caused by housing resonance. The anomaly was determined to originate from structure-borne sound generated by forced vibrations induced by the loudspeaker during low-frequency operation. Accordingly, this paper proposes an improved sound source structure for impedance tubes that suppresses structural sound generation by isolating vibration transmission paths and optimizing damping design. Comparative experiments measuring the sound absorption coefficients of black sponge material using the original and optimized sound source structures demonstrate that the optimized structure effectively eliminates the anomalous peaks in the low-frequency measurement results. These results validate the effectiveness of the proposed approach in mitigating structure-borne sound and enhancing the accuracy of impedance tube measurements, thereby offering a feasible technical pathway for the independent development of high-precision acoustic testing instruments in China.