@stereo5 , you will a 12" sub to produce anything useful below 50 Hz. Just a caution, bass travels...far. When my system is on playing something with a lot of information below 30 Hz things on the opposite side of the house rattle and buzz like crazy. This may cause trouble in an office environment.
Subwoofer Recommendations
I am looking for a single subwoofer that will compliment my JBL L100 Classic speakers. This is my office system and I only want 1 subwoofer (no swarm) to add a little oomph below 50hz. I will be using it with my McIntosh MA6600 on the second set of variable line outs. The sub has to accept line in, have a phase control, level control and adjustable crossover so I can cross it over under 80hz or so. I will be still running my JBL speakers full range. Price is up to $1500.00 new or used although keeping it at around a grand would be great. This is the only way I will hook up the sub and I would like something that does go deep. I know there are probably hundreds of subwoofer threads but I have never looked at them. This is just something I came up with today so any help would be appreciated.