I'm no audio buff, but have in the past spent decent money on speakers and audio kit for car and house, and know you prob need some direction in what you are wanting.....[smilie=confuzzled.:
From what I've learned......all speakers have an efficiency rating and buying hifi speakers with a higher efficiency rating will mean less powerful amps can drive them easier but if you end up buying a speaker with a low efficiency rating and you'll need some real grunt (i.e. serious amp) to move the cones with any real firm control......otherwise yoiu'll end up with a crappy wallowing bloated sound.[smilie=romanjury.g:
With the Civic cabin letting in so much road \ tyre noise I don't think it's worth spending much to be honest. I opted for the Honda speaker updgrade option (as was offerred this for next to nought as part of my purchase) and reckon the sound is OK.......nothing great but does fine and marginally better than the bog standard speaker option.
If you want LOUD [smilie=happydance.:...and not sure what you mean exactly

other than having more low end oomph from the cones... then your best speaking to an auto audio shop guy as amps \ speakers combos might give you what you want in conjinction with sound dampening options....
I spent money years back in putting in a pricey head unit, speakers, sub and cabling in an astra and it sounded great if sitting in the driveway or movving at 30mph.....but start driving above 40mph and noises on the move made the expenditure kinda pointless as the majority of the clarity of sound wa soon inaudible once road \ tyre noise got up.......I'm sure others will disagree but that's my experience....unless your gonna sound proof the whole of the vehicle.
If you were driving an Audi A4 with such a quiet cabin....then spend spend spend, but I just don't see the point in the Civic...and believe it or not I lurv my car! [smilie=grinz.gif]
Just think road noise in this model is higher than it should be!
Good luck in your upgrade........