Volume and port area recommendations?

Jonnyswboy · May 4, 2022

Designing a box for 2x Fi SSD 18s and am not sure what volume/port area to use. Tuning to about 38hz and plan on ~14ft3 net.

Fi recommends 100in2 for both but that seems low to me. WinISD and speakerboxlite are giving me completely different port velocity numbers so that isn't helping. My gut says two 8" aeroports would be good.

SlugButter · May 4, 2022

2 8 inch aeroports should work fine. On a slot port 100 is too small I think. 12-16 inches per cube is a good rule.

hispls · May 4, 2022

Jonnyswboy said:
Designing a box for 2x Fi SSD 18s and am not sure what volume/port area to use. Tuning to about 38hz and plan on ~14ft3 net.

Fi recommends 100in2 for both but that seems low to me. WinISD and speakerboxlite are giving me completely different port velocity numbers so that isn't helping. My gut says two 8" aeroports would be good.

I have not personally had great luck with multiple round ports vs single ports but I've seen others do well with them. I would also be looking for a lot more port area especially if you plan to throw some power at this.

Jonnyswboy · May 4, 2022

hispls said:
I have not personally had great luck with multiple round ports vs single ports but I've seen others do well with them. I would also be looking for a lot more port area especially if you plan to throw some power at this.

Planning on clamping 3k. I'd go for a single 12" but I can't source one afaik.

Bobbytwonames · May 4, 2022

Jonnyswboy said:
Designing a box for 2x Fi SSD 18s and am not sure what volume/port area to use. Tuning to about 38hz and plan on ~14ft3 net.

Fi recommends 100in2 for both but that seems low to me. WinISD and speakerboxlite are giving me completely different port velocity numbers so that isn't helping. My gut says two 8" aeroports would be good.

It sounds like you need about 200 sq. inches. Maybe they meant 100 sq. inches each and not total?

Jonnyswboy · May 4, 2022

Bobbytwonames said:
It sounds like you need about 200 sq. inches. Maybe they meant 100 sq. inches each and not total?

Jonnyswboy · May 4, 2022

Both 2 8" ports (100in2), same length, volume, power, t/s, etc.

WinISD

Speakerboxlite

Bobbytwonames · May 4, 2022

Jonnyswboy said:
View attachment 38013

I just asked my box builder friend. He's knows Scott the Fi owner real good and has installed a lot of Fi subs.

Bobbytwonames · May 4, 2022

Jonnyswboy said:
View attachment 38013

7.1 sq. inches per cube seems awfully small. I would guess 170 sq. Inches at a minimum.

Jonnyswboy · May 4, 2022

Bobbytwonames said:
7.1 sq. inches per cube seems awfully small. I would guess 170 sq. Inches at a minimum.

That makes sense to me, especially when looking at WinISD. But also people run a single 8" port on (2) 12s all the time and and I imagine one of these 18s is somewhat comparable to (2) 12s. Also aeroports can be a bit undersized, maybe 100in2 of aero would perform like 150in2 slot? I'm totally lost on this one lol. I am very interested what your box builder friend says.

Bobbytwonames · May 4, 2022

Jonnyswboy said:
That makes sense to me, especially when looking at WinISD. But also people run a single 8" port on (2) 12s all the time and and I imagine one of these 18s is somewhat comparable to (2) 12s. Also aeroports can be a bit undersized, maybe 100in2 of aero would perform like 150in2 slot? I'm totally lost on this one lol. I am very interested what your box builder friend says.

Did you tell Fi how big your box is? A 2 - 12's box equals around a 1 - 15 box to me. A 2 - 15's box is pretty close to a single 18, give or take and obviously sub dependent. One 12" aeroport might work (113 sq. inches).

Jonnyswboy · May 4, 2022

Bobbytwonames said:
Did you tell Fi how big your box is? A 2 - 12's box equals around a 1 - 15 box to me. A 2 - 15's box is pretty close to a single 18, give or take and obviously sub dependent. One 12" aeroport might work (113 sq. inches).

I would if I could get one for a reasonable price. Sonotube seems like the only option but I don't want to add a flare.