Is a flat PA the holy grail?

In tandem with coherence, can we finally put to rest the idea that our goal when tuning a rig is to have a “flat” PA?

Below is a graphic Chris Gille found on Wikipedia that shows the equal loudness contour graph.

If you flip it upside down as pictured, it shows the relative frequency response of our ears.

As you can tell, that response changes as the level of sound is increased and do you notice something?  Our ears don’t perceive sound “flat”!  Because of this, a flat EQ curve on a PA sounds awful because all you’re doing when going for flat is getting equal energy at all frequencies.

Rather than working for flat, Scovi suggests the more important “holy grail” is linear transfer.  The goal is to have linear transfer of audio from the desk through the sound system with as little coloration to the signal as possible.  What goes in is what comes out.

In order to achieve this, the RTA is NOT the right tool to use – all it does is measure energy.  The correct meter is FFT which generates a difference curve of the PA output as measured in the room to the output straight of out the console.  When you subtract 5 dB at 400 hz on a channel, you should hear 5 less dB of 400hz actually in the house.