sub wiring, 2 d4's and 1 d2 woofer

Here's a recent post that's similar.  See especially i am an idiot's reply at the end.

Here's a way you can achieve equal power distribution to all 3 subs:

The left and middle are the d4's.  The one on the right is the d2.  Both coils on the d2 are used, while only one coil on each of the 4's is used.  The d2 is series-wired to make a 4 ohm impedance, and then the three 4 ohm impedances are paralleled to achieve an equally distributed 1.33 ohm load on the amp.

To see if single coils can be used in your situation, determine the power output of the amp (RMS) at 1.33 ohms (which will be less than at 1 ohm).  Find the continuous power handling capability of each of the subs, then add the three of them together.  Find 2/3 of that capability.  If it is about equal to or more than the amp's true output then the situation will be safe.

Example:  each sub is rated 500 watts continuous, both coils driven (1500 watts total).  2/3 of the sum total would be 1000 watts.  If the amp puts out about 1000 RMS watts or less at 1.33 ohms it is a safe situation to use only one coil per sub.

MA Audio HK200D