Need help with sub selection


Downsizing to monitors (monitor audio silver 3's) for a while,
with a buget of $500 (used) any recommendations on a small sub
no larger than 10" driver.

Thanks in advance
markeetaux
I use the Q108E REL with Von Schweikert VR-1s in a small room. Nice and small, bass to 30 Hz. To get lower you will need a larger sub. I also have a beautiful Hsu VTF-3R that goes to 18 Hz (-2 dB), flat to 20 Hz., but it is bigger. Great price and great service.
Post removed 
Bob, you are using the amp in the sub. Because of the very different impedance the main amp will not send any power to the sub, only a signal.
Post removed 
Bob, I think that disturbing the signal to the mains with a high pass filter or external crossovers usually introduces undesireable grain in the mains-- short of rather high $ implementations. There is no problem with bass augmentation mode with LFP in the sub as used by REL or Vel DD-- provided the system is set up carefully.