Originally Posted by Hopinater
Like sk373 said, the sealed subs have the POTENTIAL to achieve lower extension because of their design but that potential can't be realized without output. You can compare the numbers for the 15V and the 15S to see this. The 15S has 109 dB from 16 to 25 Hz and the 15V has 126 dB in that range. However, if you compare the graphs of the two subs you'll see they behave true to their design, the 15S rolls off slowly where as the 15V rolls off rapidly after 20 Hz. So in theory the 15S has better extension.
But that extension won't be very noticeable because of the lower output. Don't forget, the lower you go the more power it takes for noticeable bass. Those low frequencies are hard to experience, they require power. Just as sk373 said, in order to realize that potential for deeper extension you'll need to have a small room or add more fire power, either in the form of a larger sealed sub or more smaller sealed subs.
The trade-off is very well explained, appreciate a lot! The main question left is what fire power is enough for 320 sq.ft living room in apartments with series of openings totaling another 240 sq ft if the goal is to be OK for 20db below reference.
Reading of compression charts on the PSA site tells me that even dual 1500s can deliver 10Hz at least -20db to reference for 10 ft distance, or even bit higher, but may be I've screwed up numbers or missed the whole point
Just in case, my rough estimate, based on upper compression line (purple) from PSA site:
1) 10Hz can be delivered by single s1500 at least at 91dB, or may be higher, as compression is not max burst, neither long term output;
2) assuming it was measured at 1m distance, correspondent level at 3m, which is the distance to my MLP, is at least 82db;
3) dual gives me +6db, so 88db, corner loading may add a bit more, but lets leave it for now;
4) reference level for home is 75 db + 10db (LFE) + 20 db headroom gives me 105db for reference;
5) thus dual s1500 capable of at least -17db below reference, assuming 0 room gain
6) my longest dimension is 28 ft, which is 1/2 wavelength for 20Hz, so I might expect 6db room gain (not 9-12, as you normally do, as there are openings) at octave below, which is 10Hz
As 5) stays within -20db to reference, which is OK for my listening levels and there is an opportunity for 6), though theoretical, ain't I'm safe with even dual s1500, set aside dual s1801 or s3000i? Hope it makes sense.
PS. s3601 is a no go for me due to size limitations