Tech support (regular "joe" techs anyway), especially at JL, will never give a response to something that may cause a higher rate of failure with their products. (Bandpass loaded woofers tend to have higher rates of failure due to the user being unable to hear the distortion clearly)
Most tech support depts. have become useless for the most part. There are a few that are still good though.
Bandpass is difficult to get right, let's put that out there to start. Wide bandwidth is difficult to achieve without the enclosure(s) getting quite large. The wider the bandwidth (typically) the larger the enclosure. Bandpass requires high degrees of accuracy for volume. .05ft^3 (in error) can change the tuning a fair amount and result in what sounds like a "one note wonder".
I agree completely that bandpass is problematic. I did a lot of work on those in the early and mid eighties. I have built three finished designs.
The first was the best. A second order band pass design using two 6" SEAS woofers, two sealed enclosures and one common vented one.
I built them for my father who was enamored with Lowther units at the time. They did the job, and they were small enough for him to take two back on the plane to England. They spanned two octaves just about.
The others were isobarik second order band pass.
The problem is that with larger drivers you end up with a large cabinet, unless you make them isobarik, and then efficiency is low.
In my view only second order band pass designs have acceptable distortion and time delay.
There are a couple of advantages to band pass second order. The roll off is second order, so you get more deep bass then with standard QB 4 alignments. You have good control of the total Qt of the system, so you can make the bass very tight.
You have second order roll off on the top end, usually around 90 Hz, which means that you can make a nice acoustic crossover with sealed second order bass/mids. However you still need an electronic crossover above the high end cut off, to stop HF radiation from the port.
My view is that for a boat you will go through a big hassle for little gain for a system on a boat if you go down the band pass route.
Some of you may remember that KEF had a huge bandpass enclosure,with mid and tweeter on top that you could rotate. Although that speaker had prodigious bass output, Qt always sounded too high to me, with poor bass articulation, despite the vari Q control in the tape loop.
This was the last bandpass I built.
It has a couple of 9" morel units in isobarik configuration. Tweeters are Scanspeak D 29s, with the dual magnet sealed extended range W75s, tow per enclosure in individual sealed compartment. Acoustic crossover is at 90 Hz.
They are very good if you don't push them too hard. It is easy to bottom the drivers. They are powered by venerable Quad 303s at the moment one per speaker. They provide 45 watts per channel, so that is 90 watts per speaker. With that power I feel there is not much chance of damaging the drivers They are in our Eagan quad four town home currently. They produce enough deep bass that I worry about complaints from the neighbors. But in the current application they are fine.
These I built just to fool around.
They use a couple of 12" Madisound woofers in isobarik configuration. There is good output from 27 Hz to 90 Hz. I set Qt at 0.5 and the bass is very tight. They are power hogs though, and you have to push them. I use them in the first level of this home. It is a big space with a lot of bass leakage, and the two KEF B 139s needed a little subtle reinforcement stating at 80 Hz. For this they are doing the job fine, but high spl subs they are not.
However with them organ CDs down there sound very impressive and they do blend well with the main speakers.
So if you really are keen to do a band pass I can try and help.
