Moving to 2-sub; What should I do?

Currently have:
RSS315HF-4 with O-audio 500W BASH amp in 68L sealed enclosure. F3 is ~36 although with the bass boost of the O Audio, it's probably a little lower.
Not ideal, I have to set the HPF at 25 Hz to avoid hitting Xmech. It's too much power. Can be pretty loud at 40Hz (which I guess is most subs)

Looking to move to a 2 sub setup so I have to decide what way to go. I want deep but not necessarily need 120+ dB at 80 Hz. I would like the ability to have deep bass, as well as eliminate any worries of hitting XMECH when I crank my system to extreme levels.

I can sell everything, but selling the subwoofer driver is not ideal as it is heavy and expensive to ship. Also, it seems that the last sub enclosure I made turned out pretty well, but it was more work than building a simple box seems to be.

Option 1:
Build a 2nd sealed RSS315HF-4 to match, sell O Audio, buy iNuke 1000 DSP or other amp to power both with ~ 300W (Total cost ~$300)

Option 2:
Buy RSS460HO-4, use O-audio amp on that. Buy 300W amp for the 315HF. Run an 18" and 12" sub. (Total cost: ~$400)

Option 3:
Blow it up, sell it all and get something different. This could include 2 Alpine SWR-1243Ds in sealed boxes, 2 FiCar x12 or x15, powered by some amp. (Total cost: $100-$500)

Wife seems to be allergic to bass, but I love bass and want to improve the quality and room-filling balance with a 2-sub setup. Oh yeah, and smaller enclosures, under 100 L are preferred. What would you do?

Hello, thanks for your reply. Currently it's in a large open room, but I hope to move it downstairs into a smaller area in the next 6 months. I should do some measuring to look at different things.

About the filter- with the 20 Hz filter engaged, I hit Xmax with 50% gain watching blu-ray movies with very low bass. One in particular is "Tron: Legacy". When listening to music, I can use the 20 Hz filter without issue.

Do your Win ISD simulations take into account the bass boost the Oaudio amp has? I had been looking at possibly modifying my amp to reduce the boost, I got the information from Oaudio to do that if I need to. They have charts so you can set the boost from 1-5 dB of boost and the Fc from 22-38 Hz.

Switch Setting - 16 Hz C1, C2 = 1.00 uF
Filter Fc = 12.98 Hz
Filter Q = 2.41
Fc dB = 7.62 dB
dB Boost = ~10 dB

Switch Setting - 20 Hz; C1, C2 = 1.00 uF
Filter Fc = 17.33 Hz
Filter Q = 1.72
Fc dB = 4.71 dB
dB Boost = ~6 dB

Switch Setting - 25 Hz; C1, C2 = 1.00 uF
Filter Fc = 23.06 Hz
Filter Q = 1.42
Fc dB = 3.05 dB
dB Boost = ~4 dB

When I first built my sub, a lot of people suggested that I build it ported (after I had the box 80% complete). But they also suggested with more than 1 sub, sealed starts to get better. Probably because sealed enclosures don't have the excursion issues below tuning frequency that ported designs have. For the record my wife thinks my current 68L sub is "big".

My current thoughts are leaning toward building a 2nd sealed and going with the iNuke 1000 DSP; would be 300W per channel roughly. But of course I am open to other suggestions.

Looks pretty good. I think you are right. The smartest thing to do would be to build this sub enclosure and try that out, and then if I don't like that I am only out about $50 in materials. Should be 6-8 dB more output from 30 Hz to 20 Hz. I'll have to run some of this through win ISD on my own just because I'm like that I guess.

I see your proposed build is 5 ft^3 (~141 L) and tuned to 15 Hz. How would you feel about 120 L tuned to 19 Hz? I would still use the 20 Hz filter as is, if possible. Looks like I would have a little stronger output between 20-30 Hz, still have SOME performance down to 15 Hz; it would be smaller and also have a little less excursion; at least according to Unibox. I'm guessing you are assuming "heavily stuffed" ? 4" would be 16" long.

The downside to this size/tuning is it looks like the port will be undersized, and may chuff near 23-19 Hz. Alternatively, 2 3" ports would only be about 19" long and would provide some relief. Of course that is all Unibox; without the filter; and most people prefer Win ISD I believe.

Cool, I am taking this project on for sure. I think I can get it done with 1 new piece of MDF, I have a TON of scrap I can use for bracing and whatnot. My plans right now are to make a 24" x 24" x 18" box, use PVC pipe for the ports, and do a double thick baffle. I also need to figure out a relatively easy way to put a speaker grill on it, and may make it a passive sub; relocating my plate amp to a separate box. Thinking about what internal braces I'll use. Not a huge fan of window braces since they are far from ideal. I have a router and some circle jigs but I don't currently have a jigsaw; might buy one. Also thinking about using the bracing to hold the ports in place. The opening for a 3" port internally needs to be at least 3" away from any side wall, right?

Probably start making this in January.

Did a bunch of simulations in winISD, and it's hard coming up with the exact design I want.

Questions relating to WIN ISD Alpha:

My air velocities seem high. I switched from a single 4" to a single 5" port. Looking around, it seems larger diameter ports can tolerate higher velocities before chuffing, so a 5" port is a huge advantage over the 4". I should be able to get 5" ABS or PVC from a local plumbing supply company, with at least 1 elbow.

The only problem with 5" is now the port is getting really long, which makes me want to go higher with the tuning. I think a 4.5 ft^3 box with 17 Hz tuning was wanting something like 37" of length, which I should be able to accomplish with 1 elbow.

Questions:
1) What are the rules for internal port opening placement? I know you don't want the opening near the driver cone, but what about the side walls. I heard you don't want the rear wall within 1xD of the opening- right? But slot ports seem to "break the rules" by having the opening right up against the wall.
2) Should I assume that the driver will "roll off" below 20Hz and therefore the exursion peak around 14 Hz will be a little bit less than modeled? Depending on box size and tuning, I either get a big peak above or below tuning.
3) Even with a 5" ID port, I still have an air velocity of 40 m/s at around 14 Hz (not sure if it would be audible or otherwise noticeable). Is this OK?
4) Is the modeled excursion 1-way or peak to peak? If it's peak to peak, then my xmax limit is actually 28mm and not 14mm.

Was looking at the possibility of buying and RSS390HO-4 and building that instead, but the only real advantage that I see over my current plans is that it could potentially take more power should I change amps later. I could get the 390 for a mere $139.99 shipped today. Actually would like to buy an RSS460HO-4, but that's a lot of money and I'll always think it's underpowered with only 450W.