mtx 1501d pulling how many amps?

I left the last topic about wiring the MTX 1501D. Ok I also purchased 2 MTX 8512-04 subwoofers, each with a 500 watt rms. I talked to an installed I know, and he said that it doesn't matter whether you run 500 watts at 4 ohms, or 1000 watts at 2 ohms, you'll still be pulling the full 140A at all times either way.

Is this correct? This seems kind of off to me. I would think that if I only had one sub hooked up and the gain set accordingly, that not more than 50A would be pulled. Am I thinking right, or is the installer I talked to right?

Any input woud be great. Thanks.

The installer you know is not correct in this regard.  I'm betting that he is confusing a couple of different things:  the amplifier WILL supply full power at all times regardless of gain setting, but is dependent on the impedance load to produce that power.  Logic in itself tells us that 1000 watts of power is greater than 500 watts and therefore will pull more current to produce.  But Ohm's Law explains the logic.

If you know power and system voltage, you can arrive with a fairly reasonable estimate of current.  The voltage is that of the vehicle's power supply, let's say 14 volts.  Power produced by the amplifier will be less than that which it pulls because of necessary inefficiencies.  If the amplifier is 60% efficient, it will pull 1666 watts of power to produce 1000 watts at the amp output stage.  Use this higher "pull" power number in the Ohm's Law formula.  I = P / E (current flow equals power divided by voltage).  1666 watts / 14 volts = 119 amps.  At 500 watts output (833 watts pulled), current is half of that. 

Here is a formula for considering efficiency:

e = efficiency of amplifier

total RMS = watts demanded from source

(RMS X 2) / (e X 2) = total RMS

Then use Ohm's Law I = P/E to find demand in amperes.

This is the general rule for wiring a vehicle for power:  supply wiring and fusing to handle the total capability of the amplifiers, even if lower-than-maximum loading is actually used.  The amplifier fusing is the key to go by.  The reason for this is that the car is likely to be in someone else's possession after you are done with the installation and you have no control on whether they switch subwoofers or other speakers to different loads.  In the event it is your own vehicle you can supply power wiring and fusing for the way it is set up...but you have to remember that the wiring may not support a changeover to a lower impedance / higher power output.  It's better to have the wiring done once with regard to amplifier's maximum capability.  The load can be changed by anyone at any time and the wiring will still be sufficient.

But I will have to admit, I usually wire my personal systems only to the extent that I use them.

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.