Advise on system choice

[buggsson]

I started a thread some days ago, asking advice on choice of mid/woofer drivers, but concluded that I might be better off by first deciding on which system to go for. I know beforehand that some of you might think that I am going way over my head, and maybe I am, it's the way I am. Even if I, as a result will build something for the scrap yard, I will have gained experience, and I will have some nice drivers to hopefully build something better of.

So here it goes:

At present I have three kinds of systems in slightly different forms. I will leave out driver choice for now, if possible. I have some subwoofer drivers to suggest that I hope will fit to each different system when the time comes to start the driver hunt.

I have a few goals that I will strive toward, such as that I am planning to go sealed, low frequency goal in the 20-25 Hz region, will cross actively. For SPL, I don't have a clue as to what I might need, I'll start with 100 dB, as it such an even number. Even though my better half suddenly, "as a lightning from a clear sky" gave me a "carte blanche" regarding what I can build, I feel that size is a consideration, to a point. They cannot be too large.

Below, you wil see that I suggest double tweeters one in a while, is that a good thing? I know I have seen both positive and negative opinions about that? Pros and cons please?

System type 1: Separate, rectangular subwoofer box containing 2 x 12" in push/pull or 2 x 15" with isobaric loading. On top of that I will place a smaller box. I would prefer a MTM, or perhaps a TM box. I believe the MTM is preferable, is it?

System type 2: Like the EgglestonWorks boxes, like the Andra II or Savoy. For the woofer section I would think that I would prefer the same configuration as in my type 1 system above. For the mids and tweeters, I don't know. If I go for example MTTM, the tweeters might be to low for a good listening position? What kind of impact does the vertical positioning of the mids and tweeters have on the end result?

System type 3. A relatively large, rectangular box, more high than wide. I have been thinking of doing either WWMTTMWW using 9" or 10" subwoofer drivers, or WMTTMW using 12" subwoofer drivers.

For all systems above, I might as well skip the second tweeter when two is suggested. And I do not really know if my planned frequency and SPL goals are achievable as is. If need be, I might go vented if nothing else will help.

Eventually it will emerge sound from whatever system I finally choose, but I might not like it.

I would like input, pros and cons for the different systems I have outlined above. It is just rugh outlines, but I would like something to start from. Personally, I have taken a liking for the third system, but what I will end up with is far from known, as yet.

I am likely to have forgotten a lot information that is needed, but this might serve as a start?

[MaVo]

When size is critical, look for pro audio woofers, as their strong motors need only small cabinet sizes.

above that, i would use a compression driver instead of a complex m/t combination. maybe a bms coaxial driver when low crossover to the woofer is favoured. that system would be small, efficient, with high headroom = low distortion and a more coherent sound because you have less crossovers and drivers.

[buggsson]

Aren't pro drivers hard to get to go real low in a sealed application? They all have quite high Fs. If that is not a good parameter, which is? If they can go low sealed, can you give a few examples, because I did try to find pro drivers as well.