A resonance bump in a room's frequency response is called a room node. Bass traps substantial enough to control nodes have always been expensive to buy or intricate and time-consuming to build - not anymore.
The MegaLENRD Bass Trap (Low-End Node Reduction Device) is extremely effective at smoothing out low frequency room nodes and is just a bigger version of the original best-selling bass trap. At twice the width (extending 24" along each wall, not 12" like the standard LENRD,) the bass trap is substantial enough to handle low-frequency problems in rooms of any size and is the only broadband absorber effective below 50Hz.