I wanted to build a high efficiency speaker to work with my low power valve and SS amps. These Spanish designed and made 12" concentric drivers by Beyma (12XA30/Nd) filled the bill. The woofer section is 98db efficient and the tweeter section 105! Because these drivers have a very low Q only a 30ltr ported box is required but also a result of high efficiency and low Q there is not a lot of low bass. Sub-woofers or bass drivers are required if you like your low bass. The woofer cone is heavy and quite stiff the the domed concentric tweeter is titanium. The drivers and rated at 350W! The magnet assembly is extremely powerful and uses neodymium magnets.
The boxes are heavily braced inside and lined with bitumanised heavy Al tape and a layer of dampening. The external Xovers are very simple crossing from the woofer to the tweeter at 2KHz. There is a -6db slope on the woofer and -12db slope on the tweeter. The finish is one I have developed myself by using a roller to produce a very stippled, sonicly damp layer. Grills are magnetically attached. The overall sound of the speakers is detailed.