How many subs?

I now have only 1 sub. No delays. No DSP. It is in the front left corner and 180 degrees out of phase. It uses Rel’s high level input from both L and R.

I found whatever I did, multiple subs interfered with the sound from the main speakers.

It sounds great - that is what counts.

What has become apparent, is my floor.  Vibration through it.  A timber floor with construction involving stumps. I have plans (that will likely be never done) of removing the carpet, ripping up the floorboards, removing the structure, levelling the ground and then preparing it for a concrete pour. No formwork is needed as the brick foundations of the walls will provide that.

I haven’t looked into if it actually needs rebar, but I’ll go there and have fun making it up as I go along. After watching a 5 minute video on YouTube of course. In addition to what might look sensible, I’m going to incorporate an immature shape into it and know it is there.

I have a couple of friends that can weld - they would find my plans funny. Both know about concrete foundations so I don’t need to waste 5 minutes on YouTube.

Then open up a window, get the 2 (?) concrete trucks and pour concrete through.

Floorboards back on top and carpet. It will likely still need a lesser form of joists between concrete and floorboards - or I ditch the elderly floorboards and use something else.

I could lower the floor which makes the possibility of tripping into the hallway at some point likely which I approve of and I think everyone else would too.

I found whatever I did, multiple subs interfered with the sound from the main speakers.

@bilateral In that case they weren't set up correctly. The most common problem is crossing them over too high!

Here's a  tip for your sub. Point it at an angle towards a wall; imagine bouncing the bass wave off of the wall in a manner similar to a cue ball in pool. This will allow the bass to be more able to not form standing waves and might sort the room out nicely.

My main speakers take a nose dive at around 58hz as designed (test CD used to verify this, Heresy III with titanium mid and tweets, better sounding than IVs with poly mid and no horn throat...I tried 'em, IIIs sounded much better). I have 2 older RELs, both kick in at 58hz and work amazingly well. I don't recommend bouncing a cue ball off the wall as it could be bad if you stepped on it in the dark..