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A 3 cf sealed box(Qtc of .514) with a 3600W max input(CE4000 on 220) will have 26mm cone excursion at 10Hz, and 10-20mm from 50Hz down to 20Hz. Is that accptable margin of safety?

For these drivers yes.

To contrast, a LMS 15" with 2 of the AE 18" PR's tuned to ~16 Hz will have the same max SPL output, but will be still cranking out 114db at 16Hz. The question is, is it worth it?

It depends if you feel you need the extra output at 16Hz and up at the expense of say 10 Hz, which for me is perfectly acceptable. Nevertheless the LMS ultra models pretty good in a sealed enclosure... and that's its major strength (very linear even in a small enclosure)... so either option will be great.

The 1600g PR's are on sale for $100 each, and then I would need some kind of filter.

I wouldn't worry too much about that with such a driver, but you may use a 13 Hz high pass if you want.

Are room gain db's sonically equivalent to PR dbs? Does room gain apply in the same manner to the PR box, increasing my headroom even further?

I don't quite understand your question, but a PR acts like a port... A PR will add low frequency extension down to the tuning point.

Two of the "high profile" LMS builds(Jai and Robert's) went with PR's. I would love some opinions on this sealed vs. PR topic. Thanks!

For any other sub, I automatically recommend a ported design, but with such a capable driver, you can't go wrong with any design. Ilkka's measurement threads will help you decide, you must have a look!!

 

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Your room will affect the PR enclosure and sealed enclosure the same way. If you room has 12db of boost at 20 hz, both alignments will be affected by it.

Are you modeling both drivers off of the 3600w? I'm showing that one driver would be over 45mm excursion at 10hz in a 3ft box with that much power. The drivers are 4ohm so the CE4000 will be giving about 1200w to each if you run both off of one amp. Use a 3rd order Butterworth HPF at 8hz in your modeling. That's what's in the CE4000. If you reduce the box volume to 2.4ft per driver you should be ok throwing 3600w to each driver with no filter.

Hi Josh,

Are you using peak excursion while modeling? If so I don't think that is really representative of program material. I use RMS instead, moreover throwing 3600W at 10 Hz in a movie is not very likely to happen, so I guess the 45 mm won't happen in real life either. I believe peak values simulate sine waves more than anything else so I'd keep the 3 ft box to benefit from better efficiency down low :T

 

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Mike, what do you mean??
RMS excursion is less than peak excursion at a fixed power input (check WinISD).

 

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Yeah I see what you mean.... exactly. To represent program material, modeling should be using the RMS value of cone excursion regardless of peak excursion. That is IMO more realistic unless one plays sine waves...