Couple of days ago we improved our 2nd control room as it had some serious issues with bass frequencies after changing furniture and getting new monitors.With some measurements and brain melting calculations ? we managed to reduce the reverberation time below 125Hz. It is way more efficient than filling the corners with rock or fiber wool!
By building a „wooden membrane“ inside a box, the bass frequency would stimulate the front panel to vibrate and to produce the same frequency only phase reversed. + & – is 0 so the frequency is getting absorbed.
See some results in numbers ? The green graph is before and red after treating.