Sundown nsv2 18 enclosure recommendation seems off...

[DiBo]

Building an enclosure for 2x sundown nsv2's and the woofer displacement and ported volume seem wrong to me. I believe it was .17 displacement ( for an 18?) And 3ft² sealed and 4ft³ ported. If these specs are indeed correct then I don't have an issue but before I build this box is there anybody that can verify that this 18 will work in an 8ft³ ported enclosure? This sub also has a high Qes and low fs which makes it a great 4th order woofer. Anyone have any idea of what the sealed side would look like? Suggested parameters are 3 foot sealed and 4 foot so do I just make a 6-foot sealed section if I decide to do a 4th order?

[DiBo]

Enclosure recommendations are accurate. Guess I'll be building an 8ft³ box for 2-18's... That just sounds off to me. We'll see what happens.

[Joe X]

Overtime Ive seen faulty driver displacements at least from sundown and RF they were later fixed, as for 4 net for a single 18" Zv3 18s worked in that same space, best is to model the driver to make your mind about what you are being given. Sometimes there's a catch running a sub specified for low operating net airspace.

[DiBo]

By model you mean plugging in box and woofer specs to see response curve rt? That's a skill I have yet to learn. Definitely on my "must learn" list. If I post enclosure specs here can you model it for me? I'll be learning this very soon. 

48x20hx30d

Port 17.5x7.5x30

1.5" port thickness .75 baffle thickness. 

Triple baffle

[Joe X]

So let's try their ported recommendation (4 net) and a 6 net alternative ( yellow plot ) picked 3K per driver for power:

 

 

You can see that 4 net projected performance will be near flat, the 6 net peaks more and you are getting  more output for your power, the SPL guy will pick 6 net of course.

Now the excursion plot, they say it's above 2 inches peak to peak assuming it's linear excursion Xmax would be say 2.2 inches p-p/2= 1.1 in or like 28mm:

 

 

Again assuming they are giving linear excursion, there would be no problems even if the box was 8 net per driver.

Finally here's vent airspeed, just me picking a port area to match 23-24 m/s peak airspeed:

 

 

 

Results are 60 square inches per driver for 4 net per driver and 70 square inches per driver for the 6 net.

So if  the question is if you are limited to 4 net with those drivers then the answer seems no even if you are over powering some. Will work on 4 net? Yes in a flat like alignment losing about 3dB of tuning bass to the 6 net,

[DiBo]

So I can go basically build this 4-6ft³ with 60-70sq in of port area. 4 nets a flatter response and 6 gives me about a 3db bass boost. 6ft³ net doesn't seem too peaky at all. I wonder why Sundown recommends 4ft³ when 5-6ft³ seems the better recommendation. I appreciate the lesson sir. 

[Joe X]

Fi gives you a range to work with but I guess is more appealing to someone looking for a driver that works on a small box to see it's specified for a small box than to be given a range.