Found some answers while searching the net.
Just figured that I'd share what I found with you guys...

Why does speaker impedance change with frequency?

The function of a speaker is to produce a constant sound pressure level for a constant drive voltage across a defined frequency range. Power is calculated as voltage multiplied by current. If the loudspeaker impedance drops and the amplifier voltage is held constant, then the current in the loudspeaker increases (current = voltage ÷ impedance). If the current increases, then doesn’t the power consumed increase? Yes! That is exactly what happens. If the power in the loudspeaker increases, then why doesn’t it play louder? Because the speaker efficiency is changing. As the speaker impedance decreases, its efficiency decreases. All that matters is that the acoustic output remain constant.

Another info link...
http://www.swee****er.com/forum/arch...hp/t-2193.html

More info under the impedance section...
Primer - Speakers

 

impedence = total resistance in an ac circuit

that means, vol of box, vol of port, tuning freq, freq played, bpressure, temperature and the car all create some form of resistance

this is why us spl guys tune all of the above

 

The reason I brought up this topic in the first place, is partially because you see those videos companies put out showing their subs plugged directly into a 120V outlet, and just taking it like a champ.

Problem is, I have never see them say how many ohms the coil is wired for, because that would make all the difference in the world...

1 ohm in theory would be 120*120/1=14,400W! Insane...
4 ohms in theory would be 120*120/4=3,600W. More reasonable...

 

^^^^ exactly what he said.

sub's rated impedence is only one variable out of many which influence how a sub behaves, how much power it will get, how loud it will play and what the actual resistance will be.


BUT, if you want a simple answer to your original question,

the answer is - more of both.

realistically tho, the 15amp scenario would probably sound cleaner.