Subwoofer between speakers?

@immatthewj yes center between my speakers. Liked it okay  but not 100% sure.

I run several 2-channel systems and all but one of them has at least one sub. Whether a sub will sound good or even be needed in your particular system is totally dependent on your room acoustics, as many on this thread have said. Most two-way bookshelf speakers need a little help in the bottom end - the trick is just to augment the low notes without getting bloated or boomy bass. What sounds good to your ears is what's right, whether that's with or without a sub. As with so many other things associated with this hobby/affliction, experimentation is half the fun and can pay off big-time.

Why do people still post drivel like this?

Deep bass frequencies in recorded music are between 40 and 50 Hz. The lowest note in a rock band is 42.5 Hz

This is wrong on so many levels, it's hard to know where to begin. But even if a note is played at 42.5hz, in an enclosed space there will be harmonics snd room effects providing location, scale snd depth far below that level.

An excellent way to demo a high quality sub is with recordings of human voices in a large space. A church, for example. Listen first without the subs, then again with the subs. The subs will reveal the space the vocalist sings from and the audience being sung to. So it is immediately apparent that even human voices benefit from sub 30hz capability.

Then we get into different genres of music. If you are willing to have a system that censors anything below 40hz that is your choice. But personally i enjoy modern music which often has real power below 40hz, or the 'fear factor' as it is widely recognised. Genres like deep house, trip hop, drum and bass and hip hop benefit from a system that retains real power down as low as 16hz.  If you only listen to music from the previous millennia you may make a judgement that this zone is not important to you. But to deny that it exists is nuts.

Subwoofer placement is a complicated issue. I never advise using one sub. Two subs would ideally be placed in the corners with digital correction of the group delay. Without digital correction the subs are better off between the speakers against the wall with all speakers and subwoofers on the same radius from the listening position. This assumes that all the drivers are in phase with each other which may or may not be true. What you have within reason between the speakers does not affect the imaging at all. Some people are fooled by their visual perceptions. Just don't part a bus between your speakers.

On the subject of the op

Obviously every room presents it’s own opportunities and limitations. This is just what i found in mine as we installed four subwoofers.

In a nutshell, what mijostyn said. My take: dont overcomplicate, you have already done the hard work in locating your speakers. Your subwoofers, always in multiples of two, simply go alongside, with at least a large hand span between sub and main speakers, and basically on the same radius as your main speakers, just ever so slightly behind so they are a tiny bit further from your ear than the main speakers. You can adjust this by ear.

Locating Inside or outside your main speakers may be decided by domestic considerations. But i tried both, and massively preferred having the subs outside of the speakers. When they were between the speakers, it sounded as though i was listening to the main speakers through the subwoofers- that I’d created a river of sound from the subs that hit me first and to some extent blotted the sound of my main speakers.

So my advice, go with a minimum of two subs, alongside, outside and slightly behind your mains. Use main speakers with strong low end and then roll your subs in below 40hz. Ideally feed them direct from your pre amp.

Then remove everything that rattles from your listening room, and use blu-tac to damp vibrating wall art😊