Question about Voltage Formula for determining Amp Gain

[fazio93]

If Voltage of the output = sqrt(RMS Power X impedance of the speaker)

I have a Kicker 12" 800 Watt 4 Ohm Dual Voice Coil Comp VR. I have it bridged down to 2 ohms.
But if I want to determine the needed output voltage from the amp, would I use the 4ohms that the sub is rated for (which would make the needed voltage 40 V) or do I use the 2ohms that I have it set it up at (which would make the needed voltage ~28 V)

Thanks

[RJesus]

The formula factors in the impedance of the speaker.

You test the voltage with the subs not connected to the amp.

You use 2 ohms, ~28v.

[fazio93]

ok thanks.