At ground level, such vibrations-akin to low-frequency sound waves-are very small, only about the size of the vertical motions that produce them.

在地表，这种类似于低频声波的振动非常小，只相当于造成它们的垂直振动的幅度。

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The calculated results show that strong vibrating source, low gravitational level and sound medium with large density and small sound speed will enhance the levitation ability.

结果表明，提高声源强度、降低重力水平或者采用密度大声速小的气体介质有利于提高声悬浮能力。

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Booster compressor noise has the characteristics of wide frequency band, intense low frequency sound and considerably high total sound pressure level.

增压机噪声具有频带宽、低频声强烈，且总声级又相当高的特性。

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The presence of a non-obtrusive means of sound amplification creates the possibility that the device could be used as a hearing aid for those with low level hearing loss.

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