ATC Anniv. vs. REG.Active - How big a difference?

Big Difference does not exist at ATC.

This may come as a big surprise as most manufacturers offer an array of wildly different sounding speakers to suit a variety of tastes.

As for ATC, throughout most of their line differences are quite subtle. The active three ways (50 and above) are a step up in SPL and effortless clarity (approaching absolutely deafening levels with the 300) but soundwise the difference in timbre with their two way 20 or 19 is subtle indeed.

In essence you simply gain bass extension and dynamic power with the bigger models. IMHO, the Active 100's are already ludicrously dynamically overkill for most home users but to me that is what should drive your thinking - if any. FWIW: if you get any of the Active 100's or above then you have a speaker with their premium midrange driver (what they are really known for and what is used by Sting and so very many others...) To me aesthetic craftsmanship cabinetry/pride is the main issue after that whether you want Anniversary or not. Remember ATC staff don't do woodwork - that is outsourced - they are primaruly acoustic engineers - their main focus is to design and build transducers and amplifiers and sound systems for prestigious clients...a box is just a box although one with gorgeous veneer/woodwork will cost a darn site more (even if it has similar guts).

Thanks I have heard the reg. 100 actives but curious as to what the sound dif. is between the reg. actives and the anniversary's-bill

I have owned three pairs of ATCs and suggest, for the casual listener, that you look at the 11, 19 or 20s.

The active line are a better value, since they are better balanced than passive ones, which will tend to react to the succinct sounds and tonalities of the amp in question. I prefer solid state, powerful (150 watts plus), and relatively clean and neutral. Tubes usually never work well--the warmth gets overemphasized as the speakers are very precise in their reproduction.

The 50s and above require a lot of space within the room to let the soundstage and playing levels to be properly evoked--i.e. they like to be played LOUD. They overpower most consumer home settings.

The anniversary editions always feature special cabinets (a ATC hallmark--very old world craftsman) but the electronics are always their proprietary built-in technologies. Nicely matched woods--I love the Yew finish.