Physics question!

Hypothetical situation:

I have a rigid panel (let's say it's a piece of plywood) that I attach to a voice coil / motor assembly, so the motor is driving the voice coil. Since its one motor driving a huge and heavy piece of plywood, it's inefficient.

So let's say I attach 3 more identical motors (4 total) to the same piece of plywood, and wire them so that the impedance remains the same. My BL product goes up by a factor of 4 (because I have 4x as much wire in equivelant magnetic gaps). What effects will I see because I do this? Will the efficiency go up? Will sensitivity go up? Will frequency response change? (Assume that breakup modes are negligible.)

What if I went up to 8 motors, wired for 2x the impedance, what would happen then?