Playing a survival mcMMO server where only admins can take spawners (and give you cuz they are nice) and I have made a 9x9x6 (i think) room with cave spider spawner 3 levels below ceiling and 2 above floor, water floating oposite from my afk position (obviously) from 2 level height. But after asking an admin he gave me a cave spider spawner I've found. Now I am wondering if I just place the other spawner on top of the first one will it be any good? I know it wont be 100% efficient but if it will be at least 60-70% efficient I will do it cuz I don't know what how can extend the room and make them come to one place, I probably could think of a way but I am to lazy, I might just sell the additional spawner...
The second spawner will only slightly decrease the spawn rate of the first spawner (below it) and vice-versa since it will only block spawns that occur in the blocks they occupy, and for a single spawner the efficiency is over 98%. There is an additional failure rate due to both attempting to spawn mobs at nearly the same time since no more than 6 mobs will spawn within a 9x9x9 volume centered on each spawner but with an average of one spawn cycle every 25 seconds (once every 10-40) this isn't much of an issue as long as they are quickly removed (make sure they fall more than 4 blocks below the lower spawner before being carried to the collection point, so you'll want to make the floor deeper). I'd say that the efficiency for each spawner would be closer to 90%.
You could also make another spawner room next to the first one, or a single 18x9 room with the collection point between them; since the activation range is 16 blocks (spherical) you can have them up to 32 blocks apart, and have even more spawners without undesired interactions (for example, 9 spawners in a 3x3 grid with 8 blocks between each spawner, or 19x19 total; if you stand 9 blocks below the center spawner the distance to any corner would be sqrt(9^2 + 9^2 + 9^2) = 15.6).
Yup, I thought of someting I should have thought about before...So the water is leading to a small killing room (of course) so I just made another spawner room on the oposite side from the first one, ez fix...Thank you a lot by the way.