Attempting to model ported subwoofer

[MCFuryNZ]

Hello all-

What I have:
Dayton RSS315HF
SA240W amp (18hz 2nd order rumble filter)
~3 foot length of 20" Easy-Pour tubing (1/8" thick walls)
Precision port 4" x 17"

What I'm trying to do I figure out what the heck size to make my enclosure. I read on a forum that PE recommends a 3.5 cf box (100L) tuned to 21hz for the Reference, so that is one of my options. The issue is that it seems like I might have room gain issues above ~20hz, since I don't get rolloff until that point.


My other option is to get my response looking similar to the LLT Sonos I see built, and I think 154L @ 18hz does the trick, especially with the rumble filter in mind.

Excursion in the 100L box is at 11mm Xmax, out of 14mm. The 154L takes full advantage of the Xmax, right at 14mm at 240w.

I can't accurately say what room gain will be like because I'm moving out in 6 months or so and don't know what the room will be like. Sorry for the ambiguity, but I haven't really figured out the best plan for this driver yet. The modeled curves are attached. Note that the Unibox curves are without the 18hz 2nd order rumble filter.

I know uncertain room gain is a huge issue, but I'd just like opinions as to what people think is the prettiest all-around curve.

Thanks!!!

[rc white]

reflex alignment

At Rod Elliots website, "ESP" in the articles section I have an article called, "compliance scaling",

http://sound.westhost.com/articles/cscaling.htm

this illustrates a method of specifying a f3 for a given driver then calculating a suitable box for it.
In the article I concentrate specifically on qb5 filter assisted alignments because these greatly increase the excursion limited output, (it should be reasonably easy to find one for an 18Hz. hi pass filter).
rcw

[ThomasW]

Sort of counter productive to have a sub tuned to 18Hz and use a high pass filter at the same frequency.

[MCFuryNZ]

Sort of counter productive to have a sub tuned to 18Hz and use a high pass filter at the same frequency.

I agree, but the rolloff seems to work somewhat well overall on my winisd plot, but of course I'm not sure if it's advisable still, which is why I'm here.

[rc white]

The 154 liter box tuned to 23Hz. plus the filter, (should theoretically be 23Hz.), is very close to an exact B6 class II alignment that doubles the effective output down to the cut off frequency kp = 6.4

this is the alignment that the driver is optimum for, although you can get much the same overall in a 90 liter box by driving from an amplifier with 1.5Ohm. source impedance.
rcw