But you have space on the other side of the walls... at least 2 of them! Let me explain what I mean.
You're working a 30Hz problem. You've been looking at options using panel absorbers, but room size limits how far you can space them away from walls, so let's look at other options
- diaphragmatic absorbers
- Helmholtz resonator
- modified Helmholtz resonator (slats/perf)
The issue is finding one that both fits and has sufficient absorption to make it worthwhile. Slats and perfs both have the disadvantage of needing lots of space behind the panel (roughly 30" for 30Hz) when other parameters are realistic. Diaphragms have the panel mass as an added parameter, allowing you to trade off depth. Helmholtz resonators are more volume-based, so you have the option of locating the resonator cavity outside the room. The downside of Helmholtz is locating them for best effectiveness (high pressure region) and the relatively small effect per unit (need multiples). Slat and perf resonoators are modifications of this, with a lot of depth required at 30Hz, in addition to construction complexity (need precise construction).
That's why I like diaphragmatic absorbers - diaphragm mass can be traded off for device depth, and they're not high-Q devices so more forgiving in practice. They're easily built large enough to be effective, and since they look like a wall, they're unobtrusive (assuming the resonant cavity is on the other side of the wall). The formula is on page 201 of Everest,
F0 = 170 / SQRT(surface mass density x cavity depth)
and the following pages show construction options. I'm seeing 30Hz options like:
- 1/8" glass (1.67 lb/sq ft) with 20" cavity
- 1/2" sheetrock (2.08 lb/sq ft.) with 15" cavity
Beats the heck out of 30-40" depth!
I asked about bass escaping because it's the other possiblity: Reflection + absorption + transmission = 1. We've been talking a lot about reflection and absorption, so I'm just being complete...
The asymmetry is a result of construction. While you have built all sides the same, your rear and left walls are backed by cinderblock, while front and right walls are free-standing. No matter what, the freestanding walls will flex more, and reflect less, especially at very low frequencies. That's all.