一、知识结构声乐声三特征噪声的危害和控制二、知识要点（一）长度的测量长度是表示物体长短的物理量．1．长度的国际单位及换文国际单位是米．常用单位，还有千米、分米、厘米、毫米、微米．换算关系是：1千米一1000米，1米一10分米，1分米一10厘米，1厘米一10毫米，1毫米一1 First, the knowledge structure of vocal sound three characteristics of noise hazards and control Second, the knowledge points (a) length measurement length is the physical length of the object. 1. The international unit of length and the exchange of international units are meters. Commonly used units, there are kilometers, decimeters, centimeters, millimeters, micrometers. The conversion relationship is: 1 kilometer to 1000 meters, 1 meter to 10 decimeters, 1 decimeter to 10 centimeters, 1 centimeter to 10 millimeters, 1 millimeter to 1 meter