With just this much information I doubt that anyone could accurately answer your question. A number of things come to mind such as:1. How much sensitivity do you require from your woofer array?
2. Have you taken baffle step compensation into account?
3. Do you plan to power taper your woofer line?
3. Can your amplifier drive the 4 ohms load without shutdown?
and so on.
Perhaps you could provide us with some more details and we could address your impedance question.
Jim