XP Grinder Optimization

Question

I have just completed my 3rd version of an XP Grinder. I created a 33x33 room, placing water along the North and South walls which run 7 blocks towards the mid-line of the room, dropping down to an 8 block run to the edge of a 3 wide trough running East-West. The trough has a 3x3 drop hole at the top of a 5x5 walled drop falling 20 blocks to my killing area.

1) I need to optimize the killing area to allow XP to flow out while the mobs don't. Short of placing an lever controlled iron door (ugly) in the walled enclosure the mobs fall into, I am getting frustrated (idea lock, brain dump, whatever...). Thoughts?

2) Is there any benefit to placing a second layer of spawners 3 spaces above the ones already placed? My spawners are set 2 blocks above the floor under them, allowing mobs to pass beneath them. I have a glass floor 2 blocks above the highest spawners (observation area), and 1 torch in each corner for minimal light. This area obviously would have to be moved up, but not sure if it's worth it. The basic set up is as follows:

• Glass
• Air
• Air
• Spawner
• Air
• Water
• Floor

The spawners are set up on a 5 blocks spacing around the center, using 32 spawners.

Thoughts? Suggestions?

Thanks!

Answer 1

Use water to push them into a shaft that's(I believe 24 blocks?) deep so they have half a heart left, use a half slab so they can't get out but you can still hit them. Due to MC spawning mechanics, it would only help you if you put the second spawner 16+ blocks away.

Answer 2

1) Have them fall into a shaft, where you can hit them, and they can't hit you. You can punch their feet and get xp.

2) The amount of spawners in one place will not make much a diffrence, but it is better to have them in different rooms, since more room to spawn would have a lower chance of a failed spawning.

Answer 3

Not sure about the second q, but for the first one, you could put down an iron bar and have them fall onto that, then the XP would flow out while they would take the fall damage still.