subsonic whistle

例句：

1. 1.The sound of the subsonic whistle echoed through the valley.
   亚音速哨声在山谷中回荡。
2. 2.The subsonic whistle was so faint that it could barely be heard over the noise of the crowd.
   亚音速哨声非常微弱，几乎无法被人群的嘈杂声所掩盖。
3. 3. The subsonic whistle was used to signal the start of the race.
   亚音速哨声用来发出比赛开始的信号。