Hi Gene:
The only reason I feel bass reflex and sealed subs should be compared separately is that the intended application for each type of acoustic alignment is generally quite different.
Our sealed line-up is designed for use in small to mid-size rooms where a significant amount of room gain (transfer function) is present. We optimized the anechoic roll-off profile of the SB12-NSD and SB13-Plus (the first two of the SB line to launch) to take advantage of this room gain, and the result is generally a flat in-room response (starting below the modal/pressure transition frequency) to very deep frequencies.
OTOH, our vented line-up was designed for a flat (critically damped) anechoic FR to the system corner frequency, and will work well in larger rooms where less room gain is present and more sheer SPL capability is needed from the subwoofer at the deepest frequencies.
Of course that doesn't mean one of our bass reflex subs can't be used in a smaller room - they can. We included a room gain compensation menu option in the new DSP amps for Plus and Ultra models which is adjustable for both slope and frequency.
The room gain comp option isn't available on the NSD amp, but the near universal presence of auto-EQ systems on AVRs (particularly Audyssey MultEQ which does a good job with the sub channel) will usually scrub off any rising low-end response (resulting from room gain) from our bass reflex NSD models.
So in summary our sealed and reflex subs are intended for different applications and measure quite differently anechoically by design. If you are going to mix/match acoustic alignments in your comparisons, then I would recommend that Audioholics develop some type of weighted scoring system which takes into account the size vs. low-end performance trade-off generally seen when comparing a relatively small sealed sub to a much larger reflex sub. If all that counts in the scoring is SPL vs. frequency, then the reflex model will almost always score higher.
Regardless, the PB12-Plus is about 5.7 ft^3 external, which is a bit larger than your most recently stated size limit (I thought I read 6 ft^3 earlier in the thread). If there is an opening for another sub, and you want to stretch the size limit a bit, LMK - but that is strictly your call.
If you do want to test the PB12-Plus please note it has three tunes - 20 Hz reflex, 16 Hz reflex, and Sealed and I recommend testing for all three. It has a nice roll-off profile in sealed mode and measures really well in smaller rooms which have room gain. Max SPL in the deeper frequency ranges in sealed mode is naturally lower than the reflex modes, but that is generally not a concern in small rooms. Point being, it's a flexible subwoofer which can be used in a variety of settings and applications depending on the needs of the customer.
