Spl at 4 metres for listening to low organ pipes

I have never owned subs before but now want to augment some open baffles
which will be OK above 50HZ. I need one sub to come down to around 16Hz for organ music. I have two other subs that come down to high 20s - low 30s. What is a realistic SPL to aim for at about 16Hz bearing in mind that it is likely to shake and rattle the house contents a bit. I would like to feel that the fundamental is there. Enclosure cannot be two big but proving the footprint is under 60cm square it can fit in a corner behind the TV and be fairly tall although under 150cm tall would be good. Any ideas appreciated.
jamikl