Try a JBL E140 in a 22" cube. face the driver into the corner if possible. the E140, nice and efficient, inexpensive (used ones around too) and will play well down 25hz in this configuration. The 22" cube will give you 5 cubic foot internal. For home use tune the box to around 25hz and cross out of this thing at 80hz or less. This will give you a shelved response for the most part, and facing into a corner should bring you about same efficiency as your pi4's in the 25-65hz range. Bill
ps. put a pice of glass or formica on the top and it will make a killer "PLANT STAND" for the corner of you room