ATC C6 Sub- How Good is it??

I am thinking of adding this sub to my ATC setup and do not here much about it- with a lofty $9,000 price tag it better be good but how does it it stack up against the Velodyne, rel ,and the other top flight subs- any info would be appreciated- bill
I have had the ATC C6 for 7 years. No problems so far. Mine makes an audible click when you turn it on or off, and always has done - so I think this is quite normal. It has a built in X-over filter, 180 degree phase switch, level adjustement, and contour lift/base boost, and stereo XLR inputs.

This sub is used in many mastering studios for movie soundtracks and is very powerful and linear. I orginally got it to supplement my bookshelf SCM 20's that, being a small speaker, are simply lacking in the really low end.

I live in a wooden frame house and the distortions from wall vibrations and windows tend to occur well before the soft clipping circuit kicks in and the vibrations can be felt two floors above... so I would say there is enough energy there for most needs (although studios will often use TWO of these beasts)

ATC support their products for decades and provide upgrade paths as future driver improvements come along - so no obsolescence worries from rapid model/driver design changes.

Like other high end ATC speakers that are targetted at professionals rather than consumers; the C6 sub is principally desigined with accurasy in mind, weighs a ton and scores very low on the WAF factor. I am not a studio sound engineer - so I can't comment on how it compares to other pro-gear or the other high end subs you mention, which I am sure are also extremely good.

The way I look at it, if the C6 sub was sufficent to mix many movie sound tracks, such as The Lord of the Rings, then it is quite sufficient for my modest needs.
After reading a review fromm 2000 on the concept7 system it seems that the c6 sub had a big drop off around 40HZ-Is that normal for such a expensive sub- if i understand that it means that the sub loses punch under 40HZ- am i missing something or for such an expensive sub should it not be flat to at least 25HZ- bill- again you do not hear much about this sub-
I don't think you need to spend $9000 grand on a sub to have excellent bass response. Check out subs by James, the EMB1500, Manley Labs tower of power, that is supposed to be the baddest sub on the planet. You might want to check out that has a forum devoted to subwoofers.
A good sub is not just about frequency response - harmonic distortion and power output are also important. The THD is quoted less than 1 % for this sub, which is low for this frequency range and driver size. It is driven by 1000 watts. It is rare that your room will be linear in low frequency response so adjustments are often necessary (placement, notch filters)...but distortion, once you have it, cannot be eliminated and can effect clarity in lower mid range.

I think this explains the high cost, but as Shiva points out, depending on your requirements, there are plenty of good subs out there and a great many significantly less than $9000.