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. 

@mijostyn 

I agree with you, but I don't have to match the bass output of the old ones.

if the Helios is better, or as good as my originals in 3 or 4 important categories, falls a bit short in the bass, but is still impressive for it's size, I will consider that a total success.  I just returned some REL subwoofers that sounded really great.  I am enjoying the open floor space.  :)

Trigger pulled !  Money is where my mouth is !  Helios kit on order !  

@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.

@milostyn

In general, you are correct, but I am hoping there is MAGIC in this design that defies rational explanation!  :).  Designer has stated the distortion is so low on this speaker that he could barely measure it - like he has never seen before.  Also, that it is likely best speaker he has designed over 20+ years.  Thank you for the well wishes!