發送短信 : Vertical directivity of train noise

 _____      _____     ______     ___      _  __  
|  __ \\   |  ___||  /_   _//   / _ \\   | |/ // 
| |  \ ||  | ||__      | ||    | / \ ||  | ' //  
| |__/ ||  | ||__     _| ||    | \_/ ||  | . \\  
|_____//   |_____||  /__//      \___//   |_|\_\\ 
 -----`    `-----`   `--`       `---`    `-` --`