HELIOS Speaker Kit

@rop45, the Helios drivers are very good ones but even with a passive radiator that little woofer is never going to be a match for a 12" Focal driver. What I would do is build the speaker without the passive radiator (which will take redesigning the box) and cross over to  subwoofers  at about 100 Hz. 

@rop45 , it is not just bass! Reproducing bass requires a woofer to take long excursions. The smaller the woofer to longer the excursion. The Helios is a two way speaker with a woofer that is running higher and a tweeter running lower to get to the single cross over point. The woofer is really a mid woofer. The long Bass excursions cause Doppler distortion of everything else the woofer is reproducing. If you do not know what Doppler distortion is google it. Transferring the lowest frequencies to another driver gets rid of the distortion entirely and increases the headroom of the system. For full range and two way speakers the improvement is quite dramatic. Less so for 3 way systems. 

Have fun building them and good luck with the project.

@boostedis Wrong strategy. The ONLY way a small woofer has of making more bass is by increasing it's excursions. Price has nothing to do with it. Longer excursions create more distortion, much more distortion in the most sensitive part of the midrange. Read up on Doppler distortion. Systems set up like you suggest are only good at very low levels, turn them up and they become painful to listen to. If Jeff handed you that line of garbage I suggest you sell them, he has no idea what he is talking about which means he has no idea how to design a loudspeaker. 

If you want to clean things up and add some headroom you get a digital two way crossover and cross over to your subwoofers at 100 Hz. If you only have one buy another. There is no other way to make a small loudspeaker sing at high volumes. Right now you are croaking.