Setting Amp Gain with Multimeter - Complete Novice

[up_troys_bucket]

Hi there,

I have recently installed some audio items in my daily. I an reasonably adept at wiring and the install went fine. Package was a set of Focal K2 Power ES 165K in the front, a Focal P30F in the boot with a prefabbed box and a Focal FPX 4.800 running it all.

The fronts are running on one channel each 1 & 2 (as far as I understand it).
Sub is running bridged on channels 3 & 4.

Everything works fine, I just need to set it all up to it's operating at it's peak. Instead of 'winging it' by setting the gain by hand, I watched a video that indicated using voltage and a multimeter it's a step up from that. With a formula of V=square root of Power of Amp in RMS and Resistance of Speaker Load. Seems straight forward enough except I can't interpret the information on the speakers or amp.

The FPX 4.800 for example indicates:

CEA power (4 ohms): 4x120 Wrms
Maximum power (2 ohms): 4x185Wrms
Maximum power (bridged 4 ohms): 2x370Wrms

The ES 165Ks indicate:

Max. power: 200W
Nom.power: 100W RMS
Sensitivity (2.83V/1m): 90.8dB
Frequency response: 60Hz- 22kHz
Impedance: 4 Ω

The P30F indicates:

Nominal power: 400 Watts RMS
Sensitivity (2.83V/1m): 86.7dB
Impedance: 4 Ohms
Frequency response:

I am massively guessing here then that by running the ES 165K on channel 1 & 2 (left and right) they are running at 120RMS each @ 4Ω (Or is it 185RMS each @4Ω or is it 2Ω)??
Which makes the formula V= Square Root of ??RMS x ?Ω
And by running the P30F on channels 3 & 4 bridged, it is getting 370RMS @ 4Ω???
Which makes the formula V = Square Root of ??RMS x 4Ω

You can see my confusion being relatively new to tuning car audio.

I know it's a lot to take in, any advice is appreciated. I may just end up taking it to an installer to tune I just hate that I can't figure it out.

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[huberoy123 10+ year member]

ES 165K on channels 1 & 2 (left and right) they are running at 120RMS each @ 4Ω would also be my opinion.
channels 3 & 4 bridged, is getting 370RMS @ 4Ω, would also be my opinion.

I define operating at its peak, as what is pleasing to my ears. The gain control adjusts the amount of input signal coming into the amplifier. When you crank it up too high, you'll hear some seriously nasty distortion. The general idea is to turn your receiver's volume control roughly 3/4 of the way up to maximum volume, then turn up your amp gain until you hear distortion. Back it off a little, and you're all set. Fortunately, we are all born with meters (hearing) to measure sound quality. I would adjust the gain, set the low and high filters to meet my sound requirements, without any meters. Your sound quality will come from using the equalizer or sound controls on your stereo. If you want more control, use a separate equalizer or sound processor. Enjoy your music.

Just one opinion.