The most important aspect of a room's acoustic performance are its dimensions. Rectangular rooms have 3 axial modes that dominate. These modes are easily excite

The most important aspect of a room's acoustic performance are its dimensions. Rectangular rooms have 3 axial modes that dominate. These modes are easily excited and store energy which you perceive as rumbling, booming, droning, etc. A very small input can get a large room going like crazy if it is mechanically coupled to the room in any way. Even decoupled sources (your neighbor's home theater system) can easily excite the axial modes. Any dimension longer than 28' is going to pass the infrasonic threshold (20hz). This tends to be OK as you go further into it. Humans are sensitive to infrasound, but often not at this level of intensity. However, designing rooms with all dimensions larger than this exceeds the limits of most practical residential real estate. An 8' dimension would give you a 70hz fundamental. This is quite audible, but also in a range of frequencies where treatments like bass traps are very effective. The room dimension range between 10' and 28' is where the dragons live. These frequencies are audible and significantly more difficult to treat. They will cut right through treatments like rockwool and mass loaded vinyl as if they didn't exist. One of the best mitigations is to simply not have rectangular rooms. The second best is to have really small ones. Older homes tend to feel cozier because the room fundamentals are not in that weird range.