define efficient...... 250amps of current draw not really efficient the sundown 2500d draws that much and puts out 500w more. no lie the alpine i a solid amp but the stupid 2ohm is more efficient than .5 is irrelevant if the .5 amp was designed to run .5ohm
in rudimentary form:
2500watts @2ohms on 14.4v at 80% efficiency:
2500/80%= 3125 watts required to produce 2500 watts
3125/14.4v= 217 amps required to produce 2500 watts
2500 watts @.5ohm on 14.4v at 70% efficiency
70% is conservative)
2500/70%= 3571 watts required to produce 2500 watts
3571/14.4v= 248 amps required to produce 2500 watts
31 amps difference in efficiency. And the order of a magnitude difference in THD between the nendo 2000 at .5 and the Alpine 2400 at 2ohms. I do not consider an amp to be .5 ohm stable unless the manufacturer advertises and warrants that use. There are many that will do it but not stated in their specs to do so. The ability to produce more power at .5 is a solid indication that the amp will have adequate headroom and built like a tank at the spec'ed 1ohm.
As far as the SAZ2500, aside from the fact it is $300 more than the Alpine in question, is a remarkable amp in that it is virtually bulletproof at 1ohm.....and at .5ohm in most cases.....if op could afford the SAZ 2500, by all means, it would be the better amp at lower impedance loads. But, as far as actual specs and ability, the Alpine is a very remarkable amp in it's own right for the $.