I have read a few of your posts on multi-sub and positioning. It sounds really interesting and I am tempted to try it in the near future (when I have some spare money!). Your posts mentioned a few ways to place the subs (e.g. in 4 corners, one in a corner, other in mid-way of the wall etc). My question is, if my main speakers are placed at the two front corners alreay, can a sub (or two subs) be placed behind the listening position at the corners with low low-pass frequency? It sounds very different to what most 'audiophile' would do. I have a very narrow room so there is no space for subs close to the front wall.

I have always find that getting good bass is very difficult and 90% of the time my listening position is at an anti-node for some bass frequency. I have used some DIY bass trap which helps a bit but not enough, and they are huge and ugly. So I am really keen to try other solutions.

I find that subs placed closer to the mains can be low-passed higher and can also have higher amplitude. Those are what I call flanking subs because of their position in relation to the mains. With higher low-pass, they tend to smooth the upper modal region.

The more distant subs are necessarily low-passed at a lower frequency. They tend to smooth the lower modal range.