if i am powering 2 alpine type R subs 500watts rms, would it be better to get a hifonics bx1000d and run it 1000watts at 1ohm or would it be better the get the bx1500d and run it 1000watts at 2ohm or would it not make that much of a difference?
1ohm loads generally have less control (damping) over the subs than do 2ohms. if you are concerned w/spl only, it doesnt matter. but for sq, 2ohm and greater (generally).
I'm running my (2) tpye R's @ 1ohm w/450rms apiece and they are very clean sounding...so I'm not sure you're going to convince me of the 2ohm & greater theory for SQ
in "real life" listening (now i realize that's what we are referring to) you won't notice an audible difference. audiofiles and those who compete sq will stray away from 1ohm loads. most amps rate their THD (distortion level) at loads greater than 1ohm. so the lower you get, the greater the distortion and the lesser the dampening factor. again, in real life, DF would have to drop down to say 30 or so (you're currently at 300-100) to effect a significant/audible difference, and at such low frequencies the THD will not be apparent either.
what you should certainly be mindful of though is that 1ohm loads cause a greater strain on your amp. some run hotter. some don't show physical fatigue at all. my old audiobahn 8001dt (of all amps) did 800wx1 @1ohm and never ran hot. the fact that both your options are class D helps a great deal (much more efficient).
so, it is easier and more efficient to run and produce power at a two ohm load than at 1ohm. if i had an option, i would choose 2ohms.