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I built this 2 layer mob spawner trappy thing in the air. It's 24x24 but no mobs spawn inside :( No one falls down and I've opened it up several times to check; nothing inside either.

It's a standard thingy with 4 water flows, forcing mobs to the middle and drop down. As said I've opened it and nothing inside

It's dark, 100% sealed with stone.

enter image description here

enter image description here

  • 4
    Mobs only spawn in a certain radius around you, so you'll have to be at the right place for it to work. – Arperum Jul 17 '13 at 9:10
  • You aren't in peaceful mode are you? That wouldn't help... – GoodPie Jul 17 '13 at 9:29
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    What height is it at? If there are lots of caves nearby they are likely spawning in there first and not having enough 'mobs' left to spawn in your spawner. I suggest filling in nearby caves, and destroying any dungeons below you if you were unfortunate enough to get one there. – RhysW Jul 17 '13 at 10:48
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    Can you provide more details about the internal layout of the spawner and the environment you've built it in so that we can give you more than just a generic 'here's the factors that affect mob spawner efficiency' answer – Steven Cunningham Jul 17 '13 at 11:53
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    Perhaps add some light and then take screenshots? There's not a lot I can discern from complete blackness. – fredley Jul 17 '13 at 14:14
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If you are 24 meters away from the spawning floors (or at least a good portion of them), and standing on the surface of a normal world, your problem is most likely the world itself.

You see, the spawning algorithm just tries to shove mobs all over the place, shooting at absolutely random points in a great territory around you. Well, most of this territory can be ignored, as any hostile mob farther that 128 meters from you immediately despawns, but a 128 meter sphere (minus inner 24-meter cutoff) is still large.

So when you add a single dark room within that, but stand atop of sixty meters of cave-filled landmass, a chance for a mob to hit your room is proportional to your room compared to mass of caves, plus all surface at night.

The solution is to prevent outside spawning somehow. Lighting all the caves is doable, but a huge work, so the easiest way is to take to the skies. Build an orbital lift or something, and place your spawner somewhere at y=192, to be 128 meters from sea level. I prefer to build over an ocean, which allows me to build twenty-something meters lower and still not hit undersea caves.

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3
  1. The spawning floor to be between 24 and 32 blocks from you, so that mobs do spawn, but keep moving (and falling into the water).

  2. Check your difficulty. No mobs spawning at all can only mean "peaceful".

  3. The advice to seal all caverns within 128 radius is technically correct but practically not very viable. The best method to have no mob-spawnable ground removed anywhere but at the spawner is to build stairs 128 blocks above sea surface (sea, so that you don't die when you fall. You will fall a lot.)

  4. This design of the spawner will not be efficient anymore. Monsters will avoid heavily damaging falls if they only can. It can be modified to work though: monsters can't plan ahead. Create a 2 or 3 blocks high, safe fall into running water, funnel the monsters to 1-wide corridor (all with water), and only then end it with a deadly drop. They don't foresee they won't be able to return and as they crowd in the 1-wide corridor, they will push each other to fall eventually.

  5. Build your own, and have pt. 1 in mind.

Just to give you some hints, here are my designs...

Derelict of "Box", a failed design similar to yours. 1-wide water channels with 1-wide water drops simply don't work. Monsters won't sink in a 1-wide hole. And besides it was built far too low. The efficiency was abysmal. I dismantled it for materials.

enter image description here enter image description here

"Circus", a very efficient design when it comes to monster spawning. It's a hemisphere about 25 blocks radius with center above the "house", covered with a roof and with water channels funelling mobs to a drop trap from 8 gaps around the chamber. It would be a great design if it weren't made of soil. That way it requires constant maintenance as endermen make holes in the walls and the roof, letting light in and ruining the efficiency. Never make anything important out of soil. Cobblestone is better but not optimal too. Use Slabs. And plan for maintaining the insides. Circus is only maintainable by switching difficulty to Peaceful. Otherwise, the inside is a deadly trap, and a creeper blowing up the wall - a disaster. Why is it so patchy? Well, an endermen makes a hole, a creeper spots me and makes it much bigger, and the I seal the hole with whatever I have. Definitely, make your design out of enderproof material like slabs.

enter image description here enter image description here enter image description here

This is the Seaship/Mall. It's entirely made of slabs, making it Endermen-proof, and it was an excellent choice. I botched the spawning platforms layout, and not nearly as much surface is located 24-32 blocks away from the player, which makes it perform worse than Circus spawn-wise. But still, there are entrances that allow for monitoring the inside, a cut-off piston that stops monsters from going to the dead-drop (which makes expanding the design easy), a spider-harvesting attachment - spiders tend to clog the walkways if left unchecked, a music disk farm, and of course the XP farm.

enter image description here enter image description here enter image description here

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  • 1
    Is that a hemisphere in Circus? It looks like a cylinder in that screenshot. – SevenSidedDie Jul 18 '13 at 5:00
  • @SevenSidedDie: The walls and the ceiling form cylinder, but the third screenshot shows the convex bottom (from below, and disrupted by walls of the water channels). It's only the top-most part of the hemisphere (about 1/4 of the sphere circumference) -on the 2nd screen you're level with the "house" which is the center of the sphere; it would be pointless to build the steep nearly-vertical parts of the hemisphere without adding extra walkways.) – SF. Jul 18 '13 at 6:05
1

Things that can mess with mobs spawning:

  • You are to close - try to keep at least 24 blocks between you and the spawner but not more than 128

  • You are on peaceful (happens to me all the time)

Ways to improve your spawner:

  • instead of making it a square make it a plus. Ex: S = Stone W = water P = pressureplate E = emptiness H = Hole

                  SSSSSSS
                  SEEEEES
                  SEEEEES
                  SEEEEES
                  SPPPPPS
                  SWWWWWS
                  SWWWWWS
                  SWWWWWS
                  SWWWWWS                      
                  SWWWWWS
                  SWWWWWS
                  SWWWWWS
      SSSSSSSSSSSSSHHHHHSSSSSSSSSSSSS
      SEEEPWWWWWWWHHHHHHHWWWWWWWPEEES
      SEEEPWWWWWWWHHHHHHHWWWWWWWPEEES
      SEEEPWWWWWWWHHHHHHHWWWWWWWPEEES
      SEEEPWWWWWWWHHHHHHHWWWWWWWPEEES
      SEEEPWWWWWWWHHHHHHHWWWWWWWPEEES
      SSSSSSSSSSSSSHHHHHSSSSSSSSSSSSS
                  SWWWWWS
                  SWWWWWS
                  SWWWWWS
                  SWWWWWS
                  SWWWWWS
                  SWWWWWS
                  SWWWWWS
                  SPPPPPS
                  SEEEEES
                  SEEEEES
                  SEEEEES
                  SSSSSSS
    
  • Put the water up one level and use pressure plates to keep the water from spreading. Mobs don't like jumping off of ledges even if it is one block high.

Sorry for the lack of a picture, I would show you one of my designs but I'm not currently at my own CPU.

The benefit of this design is that the mobs would have a higher chance of falling into the water current unlike your current one which has an incredibly low chance. This design is also more resource friendly.

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Mobs don't spawn in if your mob farm is too high because then it's not connected to the surface. Witch gets killed if dropped down 35 blocks and ender man gets killed if dropped down 44 blocks but if you built it higher than 32 blocks it would not spawn any mobs anymore.

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This happened to me too. I built it exactly and I had no mobs at all. My advice would be to just wait. I waited and suddenly I had so many mobs spawning.

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Check if ur not in peacefull If u are go to options and turn the difficulty from peace full to normal or easy or hard anything besides peace full and then see if the spawners spawns.

Do not put torch around the spawners it doent work!!!!!

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The same thing happened to me and I saw something on YouTube and it said to stay farther away from the spawner so I tried to do this and it worked

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