Originally Posted by cyberbri /forum/post/18116735
Your first question, if all speakers are set to large, then the sub only receives the ".1" LFE signal that is encoded into 5.1 soundtracks. Meaning if you are watching something that is not specifically in 5.1 (like a music CD, or TV shows that aren't in DD), then the sub gets no signal. The LFE signal goes from 120Hz down to single digits (whether or not your sub can play those frequencies is another matter).
Second question, if mains and surrounds are set to Large and center is Small, the sub will play 1) LFE channel signal and 2) bass re-routed from center channel. Bass going to the mains only plays through the mains.
HOWEVER, some receivers have a subwoofer setting (besides on/off) that is like a bass doubler, sending the mains (or any speakers set to Large) the original full-range signal, and sending the same bass signal (below the xo point) to the sub as well. So bass is played by both. This can give you more bass because it's being played by multiple speakers/subs. But it isn't necessarily good, because it can potentially cause more problems, and pushes the receiver amp harder to drive the speakers to reproduce that bass which can eat up amp power that could be used by other frequencies (if you listen to movies or music loud). If your receiver doesn't have this option, you don't have to worry. If it does, you can weigh the options, experiment to see what works for you, and go for it.