Temixoch, the bass on the Def4 is certainly a different beast than on my Def2. I'm assuming the 1.5 is similar to the 2, w four 10" subs rear firing.
The trick to getting it right is to drop the Low-Pass Filter to 38-42Hz. I'm at 38Hz, as is Phil. It's critical not to allow subs output to bleed into, and thus smear, the mids FRDs.
At 38-42Hz, have the Volume at 5-7.
I'm at 6.5, but this is really room dependent.
Other settings w me are
PEQ Gain 3.75
PEQ Freq 31
Phase 0° (both switch and dial)
For me, the 2s were just overwhelming, I could never get them right. Yes, bass on the 4s seems less powerful, but it's tighter and more tuneful.
Get yr 4s a little into the room, they start singing here 5' from front wall, best at 8'. From side walls, 3-4'.
Then set Low Pass Filter to 38Hz, Volume at 5/10. Repeat tracks w Volume going up in increments to 7/10.
Then start again w Low Pass at 39Hz, vary Volume incrementally 5-7/10. Then start again at 40Hz, incrementally Volume 5-7/10. And so on.
At some point hopefully you'll hit on the right balance of extension, bloom and speed.
Another consideration is the 4s are down firing. Thus, footers on the Zus and type of floor makes a difference, more than the 2s.
In my old apartment w solid concrete floors, stock spikes or Symposium Rollerblocks really worked. Here, on my 150 yr old suspended timber flr w plenty of flex, Arya Audio Revopods on Panzerholz are the ticket.
I'll ask Phil to chip in.
