Home made treatment to reduce Bass bloom or resonance in a room?

Hi All,
Has anyone constructed their own panels or treatments for certain areas of the listening room or living room?
I like to listen to my audio system at higher levels; to let the music open up.
I have JBL Studio 230 speakers with a single rear port in each.
I have a problem with Low freq. blooms or resonance; especially on one side of the room.
The walls: painted drywall (sheetrock).
Floor: ceramic tile.
Even with the JBL's six feet from the wall;
I still have the same issue.
It seems like it's just coming from the wall and corner behind the A/V equipment.

I would purchase room treatment or devices if I knew they would work.
If I build my own; it wouldn't be a bad loss if they do not work.

Any input would be greatly appreciated