Rapid reflections between parallel surfaces collapse stereo imaging and smear transient detail.
Low-frequency energy accumulates in corners, creating boomy, inaccurate low-end response.
Metallic ringing from flat, untreated walls allowing mid-range energy to bounce uncontrolled.
What you hear is not the source — it's the room interfering.
Parallel surfaces, corner buildup, flutter echo paths — all visible in an untreated space.