Synergistic Research Black Box bass trap (well, "Broad Spectrum Low-Frequency Resonator Array," if you prefer). Helped clean up bass in my room (I graduated to fully active bass traps, which are better, but a lot more expensive). I got these direct from Synergistic pre-pandemic after hearing them at Rocky Mountain Audio Fest. Excellent condition, nonsmoking home. I've got the original box, too.
