The CTS-D exam guide suggests adding 20dB of headroom when calculating 70V speaker tap wattages.
It also suggests multiplying an amp channel's required wattage by 120% to add headroom when calculating required amplifier channel wattages.
When we add 20dB of headroom when calculating tap wattages from distance-to-listener and speaker sensitivity, we are told that it accounts for the difference between RMS values and peak values... and thus to use 20dB for program music, 10dB for speech, and as much as 40dB for live performance.
However, when we proceed to use the aforementioned calculated tap wattages summed together in our amplifier calculations, we are told to multiply the result by 1.2 for additional headroom. This should NOT be required for rms-to-peak level dynamism as that has already been accounted for in the tap settings.
Is this extra 20% then to assure that the customer has a bit of room to crank up the volume beyond the assumed 'target' volume? Or is this something else?