I spent the last year building my BH system (FP III, Mundorf SO caps, Gold-point 24 step attenuators, 300b Paramounts, Mundorf SO caps). Speakers are ZU Druids. I really like the single range driver concept, the staging and timing is magic, that being said, the base is lacking. I have read several posts about the value of a spectrum analyzer. The one from RS that was suggested as adequate is no longer available so I looked on itunes and sure enough there are some for the iphone. I downloaded one called Pocket RTA. Seems to be all the amateur needs. indeed it seems that although the ZU specs state that the Druid goes down to 35hz, I don't see much below 43hz and there isn;t much energy below 60hz. I think sub is needed. Has anyone used a spectrum analyzer to get a sub integrated in the right place?