How to stack spawners?

[Derren]

I already have an ig spawner and I got a new one, but when I place the new one next to my original one it didn't work, how can I stack up my ig spawner?

 

[Dababy]

place 1 spawner next to other spawner

 

[Masterburn]

I already have an ig spawner and I got a new one, but when I place the new one next to my original one it didn't work, how can I stack up my ig spawner?

Place the ig spawner on the other ig spawner and it should stack