I know nothing of the subs you listed, never heard of them, but that don't mean much, other than it's hard for me to advise one way or the other about them...
if you have one sub rated at 84db efficient, & another at say 86... yeah, the 86db one will be 2 db louder
ASSUMING THERE MEASURED EXACTLY THE SAME TO BEGIN WITH, this measurement is at 1 watt, 1 meter distance
basic rule of thumb is, every time you double the power, your spl goes up by around 3db, so at 300 watts each, the 84db efficient sub should still be 2 db down from the 86, if you doubled the power to the 84db it would then be 1 db louder than the other at 300 watts,
efficency plays a big part, cause as you can see, the 84db sub needs almost double the power to play as loud as the 86db sub...
where this kinda goes out the window a bit is, these#'s are all assuming the measurements are taken in a wide open space at 1 meter distance with no reflections, reverbirations or standing waves, but in a car this is pretty much impossible... the car will dictate the actual response, & does affect the final spl of the system...
specs are important, but don't let the numbers decide all, truth is, without your own measuring devices & serious analysis, you can only do so much with the numbers... the final real analysis is with your ear, & of course an rta
all in all though, I can tell you that speaker technology has made huge advancements in the past 8 years, & newer subs will blow you away compared to old school stuff...
the idq's were never known to be exteremly loud subs to begin with....I'd recomend going with a sub I know to be awsome...
if you were a friend of mine who brought your car to me & I had to build it with your budget & layout in mind... I would probably build your car with a pair of eclipse aluminum 10's... & I'd run them with a solid 1,000 watts.... I promise you that you'll be smiling ear to ear when it's done, No one will belive theres just 2 10's in the car when they here it...... for the money there awsome, of course there are hundreds of other subs, but these are what I'd pick in that pricerange because they impressed the **** out of me over many other subs including the jl's...
sometimes it's not about using the biggest drivers, in the end the system performance is all that matters....., it may be doable with 12's too, which I would up it to 1,200 watts if 12's are doable, but it would probably be best with 2 10's really I think...
since the subs are right behind you, but your going to be listening to a heavily delayed sound, having the enclosure & ductwork being dead ridgid & solid is much more critical than an average install... I would build the box double walled & extra dead & soundproof for an install like this, which is part of the reason I think 10" over 12" too, the whole thing needs to be totally dead for the vibration to not come before the soundwave... this is something that you may not have considered, but could ruin a crisp response & make it real muddy...
you also must have time delay ability in a setup like this also because of this heavy delay, you'll have to delay everything else to match phase..
you've got a real unique situation where you want a big system, you want sound quality, and you want to still have a whole hatch storage... everything is a tradeoff, that's how I'd do it I think...
now, ask 10 other guys who also build systems & you may get 10 different answers though..., so just take mine for what it's worth
