At ground level, such vibrations-akin to low-frequencysound 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。
2
Existing predominantly, in the VeryLowfrequency part of the radio spectrum that corresponds with the audio frequency range, we can experience this activity as audible sound.
尽管这种活动主要存在于无线电声音频率分区的超低频区域,我们还是能够通过听觉来捕捉到它。
3
Ultra low noise fiber optical microphone designed for monitoring very weak sound signals in selected frequency bandwidths.