Any difference? Just age? Any ideas how to use indoor successfully w/o echos?

That's one long microphone and it will echo in confined spaces.

is the a same as the b?
any other warnings on where and when to use?
THanks

Other than it's a long shotgun and the predacessor to the 815b i don't know much else. Best rto call AT and ask, they're very nice people and helpful as well.

http://www.audio-technica.com/about/index.html#contact

It is most definetly designed for outdoors or very large open venues.

For close quarters indoors you'd be better off using a hypercardoid or cardoid. Smething like an Oktava mco12 or a Rode NT3