试验结果表明，风扇噪声主要是宽频带噪声，并得出了在不同频率范围风扇噪声对发动机噪声的影响。
From the result, we know the fan noise is mostly a width frequency noise, then obtain the effect of the fan noise on the engine noise in the different frequency range.
针对超声探伤的特点，设计了低噪声、宽频带、动态范围大的接收调理电路。
Aimed at the characteristics of ut, a receive and adjust circuit is designed, which have character of low noise, wideband, wide dynamic range of input.
提出了一种新型的宽频带共振吸声结构，该结构基于赫姆霍兹共振吸声机理，并充分利用了软管在长度上的优势，易于实现对低频噪声的控制。
Based on the sound absorption mechanism of Helmholtz Resonator, the advantage of soft tube length is fully used in the new structure, and thus the low-frequency noise can be controled easily.
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