Are you sure you need an rt kernel? You can get realtime scheduling
for Jack with the stock kernel in Ubuntu and Ubuntu Studio.

http://www.jackaudio.org/realtime_vs_realtime_kernel


Well, since the page says:

A kernel built with the realtime patches (an "RT kernel") is needed only if:

You want to run JACK with very low latency settings that require realtime performance that can only be achieved with an RT kernel


I would say yes. I have a professional studio, so i need the best performance in terms of latency.
I wonder why they put the rt kernel out of the repos.

--
Giorgio Bał
Sound engineer

T.Rex Studio
www.trexstudio.com