Soundcheck was perfect. I had measured the transfer function, applied gentle corrective EQ, verified coherence above 0.85 across the band, and documented everything. The frequency response was ±2 dB from 80 Hz to 16 kHz. I was so pleased with myself that I took a screenshot.

Then the stage manager opened the curtain. Behind it was the full stage set: hard wood flooring, three reflective flats, a plexiglass drum shield, and a mirrored back wall that the set designer had insisted upon because it 'doubled the visual space.' It also doubled the acoustic reflections.

I re-measured. The ±2 dB response was now ±9 dB. A massive comb filter pattern had appeared from 800 Hz upward — the mirror wall was creating a perfect specular reflection that arrived at the mix position 4.7 milliseconds after the direct sound. There was a new 6 dB bump at 250 Hz from the wooden stage floor acting as a resonant panel. Coherence had dropped to 0.4 in the upper mids.

The stage manager asked if I needed to re-tune. I needed approximately forty-five minutes and a time machine to go back and attend the set design meeting.

The Moral: Always tune with the stage set in its show configuration. Curtains, set pieces, and surfaces change the room's acoustic response dramatically. SonaVyx's before/after comparison makes re-measurement fast — tune for the room the audience will hear, not the empty room you soundchecked in.