I'm looking to add a subwoofer to my home theatre setup and I'm a bit confused on what I should look for in frequency response.  My main speakers' low end response is down to 40 Hz.  I can't tell you the response in reference to gain since I haven't measured them yet.  The bigger issue is that I live in an upstairs apartment and not bothering the downstairs neighbors is a big priority of mine.  The room size is about 2000 ft^3.  
I remember reading in an interview with a music producer that he sets the max bass Q to around 40 Hz and that this is common practice among producers. So really, should I look for a sub that goes down to 20 Hz or what range should I really look for?
				
			I remember reading in an interview with a music producer that he sets the max bass Q to around 40 Hz and that this is common practice among producers. So really, should I look for a sub that goes down to 20 Hz or what range should I really look for?