Hi
Load Chapter 14 with Normal Difficulty. In this Chapter are 5-10 Specters to kill and earn this Achievement.
You don´t trigger the EMP Mine, throws EMP Grenades but we can use Dart Overlay and with this, the Achievement is very easy.
In the Video shows the first 3 Specters in Chapter 14, later in this Chapter are more Specters, well dont panic when this fail at this Point :)
regard
PS: Sry 4 english, i´m german