Soundstream PCA2000D

Yes I do I have a 235A alternator

Too make this short and simple. I am just trying to figure out how to calculate the amplifiers total rms output at 12 volts with its 75% efficientcy rating.. If you can demonstrate an equation that would be great

The amp manual says 4000w peak power output and 2000w RMS @ 1 ohm mono if that helps any...

Well my friend, it's called Ohm's "LAW" because it is always true and you can't get around it.  For any amplifier to generate 4000 watts peak output using your 75% efficiency and 12 volt nominal numbers, would require an instantaneous current draw of 444.444 amps.  Might blow your 150 amp fuse, eh?  Also, to sustain 2KW RMS output would require about 222 amps continuous current draw.  Also toasts your fuse.  If the amplifier is really capable of that kind of output, which like I said I highly doubt, then you'll need to supply it appropriately.

Cheers.

Ok if an amplifier company rates their Class D amp at  2000w rms @ 1 ohm mono what would be its total real output in watts? Class D is 70% efficent so does this mean 2000 x 70% = 1400? So basically it only puts out a true 1400w rms?

Am I correct? I need help on making calculations.

Also if this is correct do all amp companies do this?

No, if the amp is 70% efficient, this means that only 70% of the amperes fed into the amp is turned into the signal going to the sub.  The other 30% is converted to heat in the amplifier. 

The amp companies rate the actual output (watts at x-amount of volts), so the efficiency has nothing to do with the wattage coming out of the amp. 

Yes, exactly.  But

sort of contradicts itself in this way: the efficiency rating determines how much current the amp must draw in order to achieve the rated output.  This is limited by the physical capabilities of the components used in the amplifier, especially the current capacity of the power supply and power rails.  So if an amplifier is 70% efficient it must use larger components capable of higher current flow to generate its output than one that is, say, 80% efficient.

Just picking nits, I know. 

I am having trouble understanding the rule of decibels.

If I have a 2000w RMS subwoofer and I feed it 1000w RMS, then it wouldn't be a whole lot louder if I fed it 2000w RMS. It would only be +3dB louder. What about powering teo subwoofers? Both handle 750w RMS. Would they be almost as loud with only half the power?

Can someone explain this to me?