Let me modify my post. I do agree that all Avalon speakers have a similar sonic signature, just like all speakers of the same designer/manufacturer typically do. This is not saying that they sound the same however. It is also reasonable to say that all Avalon speakers have a shared technological base, although I do feel safe in stating that some have a greater overlap than others. Of Avalon's current product line-up; the Opus, Opus Ceramique, Eidolon, Eidolon Diamond are more closely related than the Arcus, Eclipse Classic and Avatar. In terms of parts, the Eidolon Diamond has a different crossover, internal wiring, woofer and tweeter (over the Eidolon). To what extent these components effect a different sonic presentation will be for you to decide. I'd be willing to bet the Eidolon is much closer in performance to the Opus than the Diamond however.