wiring 3 subwoofers

It's one thing to be creative;  it's another thing to experiment foolishly with expensive audio equipment.  Save your creativity for the design and fabrication aspect of the install, not for the wiring of electronics.

Here's an excerpt from something JL published at one time (and there are many, many similar warnings to be found):

"Additionally, if you have an idea for a wiring configuration and you do not see it here, chances are you should re-think its implementation (in other words, don't do it). You will more than likely find that the results will be less than optimal."

And the rest of the copy:

https://mobile.jlaudio.com/support_pages.php?page_id=161

"Please note that when wiring multiple drivers it is recommended that series connections between drivers be avoided at all costs. This does not include series connections made between voice coils on the same driver. For more information, please consult our dual voice coil tutorial.

https://mobile.jlaudio.com/support_pages.php?page_id=163

Why? Because all driver-to-driver wiring should be done in parallel and two 8 ohm drivers wired in parallel will yield a 4 ohm final impedance.
 
It is far less desirable to make subwoofer to subwoofer connections in series. Because of slight and unavoidable differences between speakers and because of the high likelihood of uneven loading between different speakers in a car, there will be slight differences in the mechanical behavior of the two speakers in series. These differences in movement result in induced voltage (called back EMF) being created by the speakers across the series connection. This effect causes a problem when two speakers which behave differently are connected in series because the speakers can modulate each other (cause each other to move), resulting in distortion. The problem becomes more serious as more speakers are connected in series.

A good experiment to show the effect of back EMF is the following: connect four speakers in series and short the positive and negative input leads of the series circuit. Push down on one cone with your hand; you will notice that the three other speakers will move in the opposite direction of the one you are pushing. Now, reconnect the speakers in parallel, short the inputs and push down on one cone. The speakers will not modulate each other because each one is shorted directly.

Back EMF modulation is not a concern when the voice coils of a dual voice coil speaker are wired in series to each other because the coils are physically coupled on one moving mass. Therefore, they cannot possibly modulate each other because they cannot move independently."

Here, you will find proper wiring possiblities in Subwoofer Wiring Options

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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.