how close can magnets be to one another?

I was looking to my subwoofer in such a fashion as the magnet would only be about 4 inches from the magnet of  one of the 6x9"s hanging from my rear deck. Will this present any problems with this setup or do the magnetic fields not affect one another?

I honestly am not sure if they will affect each other. I wouldnt think it would not affect eachother since subwoofers are put close to each other in some installations without dividers. But if you are worried about it, just simply put a divider or put each speaker in a box than mount it to your deck.

Thanks for the help, I just wanted to make sure that nothing would be hurt.

That's true, stevdart, but in the case of a static magnetic field, such as that in which a loudspeaker's voicecoil is immersed, interaction won't have any effect on the other driver whatsoever, whether the fields are right on top of each other or not. In the case of a dynamic field, like those of a coil in a crossover, and the fact that an external magnetic field will change the value of the coil, (and it will change - dynamically, altering the values - dynamically, introducing distortions - dynamically) it is vital that the coils be placed the way you have shown them.It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

Good to know, haemph.  Thanks!Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.