How many subs?

You might want to start by reading this. https://www.acousticsciences.com/wp-content/uploads/2024/11/Soundoctor-Barry-Ober-sub-integration.pdf

My guess is that your acoustic engineer was adding delay to your subs so they would be in phase at the listening position.

To my knowledge, all powered subs have some type of e.q. circuitry in their design which also creates a delay of a few to several milliseconds depending on the model, coupled with the delay caused by normally placing your subs further away from your listening position than your mains, you could start getting a significant delay between your subs and your mains, so I am surprised he didn’t say anything about delaying your mains since he was concerned with a 3 ms delay between your subs.

Your driverack is primarily a 3 in, 6 out active electronic crossover with DSP, that also gives you a 30 band,1/3 octave e.q. along with an 8 band parametric e.q. on each input. On each output you will have both low and high pass filters with selectable slopes. 8 band parametric e.q, driver protection and driver alignment delays. It is a pretty powerful piece. There is also software that you could download onto your laptop that would allow to to operate the driverack from your listening position. You would also use the driverack to set the volume balance between your subs and mains so one doesn’t overpower the other.

Your CR-1 gives you an active crossover with either a 2nd or 4th order Linkwitz-Riley slope. You can also control volume balance between subs and mains and both units will give channel muting capabilities.

If you do not use either unit you would want to set the low pass filter on your REL’s around 34 Hz, not 120.

I would not rule out using DSP on your mains until you have at least tried it. If done correctly the positives should be far greater than the negatives.

the drive rack was not used for purpose, it was what it could do.  I wanted a balanced product that could give delays up to 10 ms (not including latency).  When the Acoustic Engineer said 3 ms delay there and 9 ms I got someone else to program it because we could not work it out.

@bilateral unless your room is enormous you don't need any delay at all unless your subs are active at higher frequencies. But most speakers will go well below 80Hz; that's sort of the 'magic number' in most rooms; if the subs do not put out information above 80Hz they won't attract attention to themselves. Since all the bass at that frequency and below is reverberant its easy to get them to blend.

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..