How to test for blocks within a certain radius of a player?

I'm trying to make a custom crafting system, but I'm not sure how to test for blocks within a radius of players, not command blocks. Specifically, I'm attempting to test if there is a dropper within ten blocks of a player at any given time and any given place in the world. Is there a way to do this?
Best Answer
Here's another idea:
If the droppers are not crafted by the player himself, you could simply spawn an armor stand at every dropper and then use /execute @p[...] ~ ~ ~ /testfor @e[type=ArmorStand,...]
If the player can craft the droppers, you could replace every dropper in the player's inventory with an armor stand named "Dropper" and all the attributes you want. When it is placed, it automatically executes the setblock command to spawn the dropper. The armor stands should be invisible of course.
You can also do nested execute commands to avoid the problem with the command block's radius.
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How do you Testfor a player in a radius?
2. Type the CommandDetect When A Player Is At A Block/Blocks Minecraft
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