Black96Z

Does the type of music determine the size of the speakers to use?

Flaring Afro

yes i would think. if you are talking about mid/high speakers 6.5 components are the best, period. they will be the clearest. but smaller subs hit faster so if you listen to metal you'll want more small subs over one large one that wont keep up.

99Bluz28

iTrader: (35)

With really good subs the size shouldn't matter(faster/slower), within reason. I would base the sub size you use on how loud and deep you want the bass, and the space you're willing to give up for the sub box. Also you need to take into account the sub enclosure itself (size, ported or sealed, quality).

Flaring Afro

^ i dont think even a good quality 12 can keep up with heavy metal. just using as example. i think heavy metal is probably the only music that would make you think about speaker size....

KEE AUDIO

iTrader: (65)

All I listen to is metal for the most part and you can have tight sounding bass from as large as 12" subs and yes...even 15" subs. Totally depends on the equipment used and how it is tuned. You can have a larger sub with less excursion in a sealed enclosure that will make tight bass.
My preference is a single 10" or 12" sub for that type of set up. Good sound is also VERY dependant on the other components used as the midbass/midrange and tweeters are equally important. The sub frequencies in this case add kick and depth but the midbass/midrange really make things come together and blend. Good tweeters equal screaming guitars, vocals and cymbol crashes without being so harsh you get listening fatigue. I prefer silk tweeters personally but some find them too laid back.
Anyway, back to the original question. Tuning and equipment choices make the most difference. Size is more determined by what fits in your cars doors and other areas. For midbass/midrange a 6.5" speaker won't sound that much different then a 5.25" because of the frequency ranges they are working in and what sound they are reproducing therefore your major deciding factor is quality and budget.

Black96Z

i do listen to a lot of rock and metal. The only subs i have ever bought were 12's. I don't have that much experence with 10's, 15's, etc. I just want to know if the speakers I have are the right choice. My speakers have seen their better days. My subs are 7 years old.

Here is my set-up:
Alpine CDA-7897 head unit
Alpine MRV-T320 (80 watts RMS per channal at 4 ohms) running a pair of 5.25 Type-R componite
Alpine MRP-F200 (100 watts RMS per channal bridged at 4 ohms) running a pair of 6.5 Type-S coaxal
2 Alpine MRD-M500 (500 watts RMS each at 2 ohms) running 2 12inch Alpine Type-R Subs

I was thinking about replacing my head unit with a Alpine CDA-9886 and then replacing the speakers later.

Black96Z

Also I am using a Optima yellow top and i have 2 rochford fosgate 1 farad caps laying around.

Silver Rocket

15s are big and move a lot of air, not really ideal for rock
12s are in the middle little bit of bass not a big aread
10s are nice tight subs small area, relitivly good sound
8s will give you a nice tight sound but not much spl

KEE AUDIO

iTrader: (65)

This is a generalization though and a common misconception. For the most part though it would be a good basis because of what most people think are good subs and what is available to them from places like Best Buys.
15" subs have larger cone surface, potentially can move more air but a 12" sub with a larger motor structure and more excursion can move more air then a 15" sub that has a smaller motor structure and less excursion. I have used all of the above sizes from different manufacturers and it really depends on the model of the sub your using more then the size of the sub.
Here's a practicle example: take a RE Audio SX12 and a MA Audio MA150Q, The RE Audio is a prime example of a sub that would move way more air then the MA Audio's 15" sub. There is also a significant price difference of course. In fact I'd say an RE Audio SE10 would give the 15" MA a run for it's money in SPL and a CDT QES-1020 would definetly outperform that 15" sub.
That being said I have used an MB Quart PW352 15" sub that hit like a 10" sub as far as being a very nice, tight sounding sub but could hit the low end like crazy to.