The house sound tech at the Riverside Theatre swore the PA was flat. 'We had it tuned when it was installed,' he said. I asked when that was. 'Ninety-seven.' Not 2097. 1997. Twenty-nine years ago, before some of the audience members were born.

I ran a transfer function measurement. The result looked less like a frequency response and more like an alpine hiking trail. There was a 15 dB peak centered at 2.5 kHz, a 12 dB valley at 400 Hz, and the system was essentially inaudible below 80 Hz because one of the subwoofer amplifiers had been dead since, by the house tech's estimate, 'sometime during the Obama administration.'

The 2.5 kHz peak explained why every touring engineer who played the venue described it as 'harsh,' 'ice-picky,' and 'physically painful.' It also explained why the house tech thought it sounded fine — after twenty-nine years of exposure to a 2.5 kHz peak, his hearing had developed a matching dip. The PA sounded flat to him because his ears had adapted to compensate.

We applied corrective EQ based on the measurement data. The house tech listened, frowned, and said, 'It sounds muffled now.' It did not sound muffled. It sounded correct for the first time this century.

The Moral: 'We tuned it at install' is not a maintenance plan. Systems drift, components age, rooms change. Use SonaVyx's transfer function measurement to verify your system regularly — your ears adapt to problems, but measurements don't.