Is the reason you don't use bandpass boxes that you prefer to listen to music and want something for daily use rather than competition use?
A single 18-inch pro driver modeled in a 6th-order bandpass tuned for low excursion 59.3hz output showed 150dB with 20kw. A Fi 18" showed 145dB with 20kw (excursion length added). I figure it's a lot more power since we're running at x-mech here and so BL is down with all the distortion and whatnot.
Bandpass is just that, bandpass (passes a band of frequencies) and can be very efficient at those frequencies it was designed for. BUT - music isn't from say 55-66hz, so really I'm just talking about an SPL-oriented enclosure..since you won't get much outside of the pass-band.
I really think I'm just rambling..
Let's go ahead and compare two systems. They both have the same box size and relative tuning. The SPL numbers I give you are supposed to be 1 meter away in free space (aka no cabin gain from a car).
Vented:4 BTLs at 20kW (xmax 16mm without the added upgrade). SPL = 143.7dB at 45hz (Subtract what you're likely to read inside a car to find cabin gain).
6th-Order Bandpass - 4 BTLs at 20kW (7.5mm excursion) is 142.7dB. Less - BUT, we're using a good bit less excursion. Increase the power to 80kW and you get 148.7dB (16mm excursion and then after that you add cabin gain which is probably going to be like 160+dB I don't know the cabin gain depends on the car and freq). If you make the box sizes larger, power needed goes down - good in competitions with large vans. Suddenly 1/10th the power gets the same SPL. And the 27mm and extra magnet a few more dB. More power will push towards xlim for just a little more UMPHHH, but with more and more compression.
For a relation - Two JL13W7s show 130dB with 8kW.
If you want you can just ignore me I'm being all like "bla bla bla - BLAhbo Blab"
And they sound like crap, as they boost one frequency and cut the rest. And they don't give any gain over a optimal ported box in SPL...... if they did everyone would already be using them. And, the box size is huge, even larger than ported.
M.S...."And they sound like crap, as they boost one frequency and cut the rest. And they don't give any gain over a optimal ported box in SPL"
M.S. they dont all sound like crap its just the prefab bandpass boxes that have given them a bad name but a well built one with a driver suited for the design can sound nice. Theoretically bandpass has a 4 db advantage over sealed and a one db advantage over ported.
"if they did everyone would already be using them. And, the box size is huge, even larger than ported."
One of the reasons you dont see alot of people using them is how complex it can be to design a bandpass enclosure let alone to fit your space power and sometimes weight limits for daily use but you do see a lot of top spl competitors using them because of their spl gain potential over a ported box.
If you built a bandpass box that didn't boost one frequencey (didn't sound like crap) it would give you no improvement over a ported box, thats why you don't see any of those.
If built for SPL, just like a high tuned ported it will sound like crap.
Thats not true M.S. a bp box can be tuned for a flat response. Ive modeled a sub that was made for both types ported and bp and the bp did give more output. Even my image dynamics idq 12 according to their own specs will give more output in bp vs ported. And theres a reason the bp is given a +4 over ported being +3 like I mentioned before. It's ok to have an opinion but your opinion is not based on the facts.
Well like I said I have modeled other subs that at least theoretically would produce a flat response in a bp with greater output potential than the ported box.
Look here and youll see the bandpass recommended for my image dynamics idq 12 does have a broader range and greated spl potential than the ported box in this case using a respected program.