PSI Audio AVAA C20 Black

The AVAA is basically a pressure cancelling device working in the lower frequency domain. All you have to do is to find a good spot where the pressure is maximized, turn it on and you are done. The result will heavily depend on the selected location. If the room modes are evenly distributed in your room (you have a room with good ratios), then the effect can be somewhat limited. But if your room has poor ratios (concentrating room modes into single locations), then the AVAA can help you a lot.
The area of effect of the unit is large but still limited, e.g. in my case a whole corner is problematic from top to bottom, which means only 2 units can cover it properly. Unfortunately there is no mounting option, so you have to figure out in this case how do you put the unit (13kg) 1.5m high above the ground.
With 2-3 units the measurements show night and day difference in the whole bass region - frequency and time domain as well. This is indeed the ultimate weapon against room modes. Of course you still have to treat your room for reflections, SBIR etc.

Pros:
- built like a tank
- no setup required
- no sound is emitted, no DSP involved
- works like a tuned absorber, but in ALL frequencies from 15Hz (!) up to 150Hz
- future proof: works in any room, can be relocated easily if conditions/requirements change over time
- the area of effect is much larger than the unit itself or a single tuned absorber

Cons:
- no mounting option
- high unit price
- a single unit most probably won't be enough
- confined spaces, close large objects can make it unstable (yes, this is true)

DIY bass traps, expensive factory-made passive traps, room correction softs, I tried it all. Some frequencies were still a pain because most of us (home)studio owners do not have the budget to build a mastering room from scratch. So some bass reflections keep disturbing the sound flow in the mix and mastering.

Having said that, we have to consider the price of the PSI Audio AVAA C20, knowing we have to buy at least two of them. You need one in each corner, ideally. That's a very heavy load on our savings, but...
You only have to buy them once!
Passive bass traps are made for the room specifically, and as soon as you change anything, like your mixing position or some furniture, your bass trap has to be adjusted. Let alone if you relocate your business to a larger or smaller room.

With the PSI Audio AVAA C20 one can just put it in the corner and it will adjust itself to the new situation without complaining.
My low-end frequency response is cleaner and steadier. I even remastered some older tunes just for the fun of relistening through them and re-releasing them on the streaming services again because of the improvements I heard.
A lot of money? Yes, but it was worth it.