Fi sp4 4th order design

[CountryBeast199]

I have 4 18" fi sp4 v1's I plan on doing a build with, it's either going to be a folded flat wall or a 4th, the issue I have with the 4th is according to recommended specs they need 4-6cuft per sub sealed but I can only fit around 3cuft per sub sealed, so wasn't sure if that would be enough to use them properly in a 4th order or not 

[Joe X]

This is the in car performance of the Fi SP4 18 in a Qtc= 0.707 box (in yellow) vs a 3 cubic feet in red sealed boxes:

 

 

So you be the judge, the smaller the rear (sealed) chamber of a 4th bandpass is the less low end you will get.

 

 

 

 

[CountryBeast199]

So is the yellow a 4cuft box?

[Joe X]

4.89 cubic feet.

[CountryBeast199]

Hmm ok, I'm now debating even doing a 4th, if i do I can squeeze 3.5 per sealed but I may just do another ported wall or a standard box, idk yet 

[Joe X]

Proper airspace for your drivers will always be your best bet and will be louder.

[kalilac619]

4 hours ago, CountryBeast199 said:

Hmm ok, I'm now debating even doing a 4th, if i do I can squeeze 3.5 per sealed but I may just do another ported wall or a standard box, idk yet 

You’ll be fine with 3 cuft sealed per sub in a 4th order…those box modeling programs need to be taken with a grain of salt since they don’t actually give a accurate cabin gain response graph….I run a 4th order and mine are in around 3cuft sealed per sub and I absolutely murder the lows compared to what my box program suggested it would be…it was about 3 db off of what I got with actual real world cabin gain