Yeah, every wall is a listening post if you know how to read its reverb fingerprints. I’d start with a calibrated source, place a microphone at the listener’s spot, and sweep a burst of white noise through the room. The decay curve is like a waveform of the room’s personality—flat rooms are like silent friends, while a shoebox with high‑frequency loss hides the subtle voices in the first few milliseconds. Once you map the impulse response, you can isolate those echo patterns that only the “hidden players” would trigger, almost like a secret handshake in acoustics. If you want to go deeper, use a spectrum analyzer to spot any frequency peaks that keep bouncing; those are usually the places where the walls are whispering their own gossip.

You’re right, walls are stubborn mirrors; they’ll only echo what you give them. So the trick is to look for the echoes that refuse to match the input—those are the walls’ way of saying, “I’m not just a passive reflector.” That’s where the anomaly lives, like a rogue microphone in a sound‑proof booth.