We decide the cross and span clearance by over-voltage times and electrical insulation strength (airspacing) from the system major in places that the public not easy to arrive.
再根据系统确定的操作过电压倍数及电气绝缘强度（空气间隙）来确定在人不宜到达地方的交叉跨越距离；
2
By varying the groove spacing, the diameter of the single or double diameter hole, and the rear air cavity depth and content, one can obtain absorption over a wide variety of frequencies.